Kaplan Anatomy 1 Flashcards

Question

25. A knife wound to the neck damages the posterior cord of the brachial plexus. Which of the following muscles would be most likely being paralyzed? A. Deltoid B. Flexor carpi ulnaris C. Flexor digitorum superficialis D. Flexor pollicis brevis E. Palmaris longus

Answer 1

The correct answer is A. The posterior cord supplies the axillary and radial nerves. Of the muscles listed, only the deltoid is supplied by one of these two nerves, specifically the axillary nerve. The deltoid originates from the clavicle and scapula. It inserts into the deltoid tuberosity of the humerus. This muscle is responsible for abduction of the arm. The flexor carpi ulnaris (choice B) is supplied by the ulnar nerve. The flexor digitorum superficialis (choice C), the flexor pollicis brevis (choice D), and the palmaris longus (choice E) are supplied by the median nerve.

Answer 2

The correct answer is C. Meiosis is cell division that produces gametes with half of the normal somatic chromosome complement. The process described is nondisjunction, which will cause one daughter cell to have 24 chromosomes, while the other will have 22 chromosomes. When a gamete with the normal 23 chromosomes combines at fertilization with a gamete with 22 or 24 chromosomes, the embryo will have 47 chromosomes (trisomy) or 45 chromosomes (monosomy). Nondisjunction can occur in either the first or second meiotic division. Balanced translocation (choice A) occurs when non-homologous chromosomes exchange genetic material in such a way that no critical genetic material is lost. Triploidy (choice B) is the term used when a cell has 69 chromosomes (3N or 3 sets), and can occur in tumors or when an egg is fertilized by two sperm. An unbalanced translocation (choice D) occurs when non-homologous chromosomes exchange genetic material with a net loss or gain of critical genetic material. Uniploidy (choice E) is the state of having 23 chromosomes, seen normally in sperm and eggs.

Answer 3

The correct answer is A. The anterior continuation of the cavernous sinus, the superior ophthalmic vein, passes through the superior orbital fissure to enter the orbit. Veins of the face communicate with the superior ophthalmic vein. Because of the absence of valves in emissary veins, venous flow may occur in either direction. Cutaneous infections may be carried into the cavernous sinus and result in a cavernous sinus infection, which may lead to an infected cavernous sinus thrombosis. The cavernous sinus is lateral to the pituitary gland and contains portions of cranial nerves III, IV, V1, V2, and VI, and the internal carotid artery. The occipital sinus (choice B) is at the base of the falx cerebelli in the posterior cranial fossa. It drains into the confluence of sinuses. The sigmoid sinus (choice C) is the anterior continuation of the transverse sinus in the middle cranial fossa. The sigmoid sinus passes through the jugular foramen and drains into the internal jugular vein. The superior petrosal sinus (choice D) is at the apex of the petrous portion of the temporal bone and is a posterior continuation of the cavernous sinus. The superior petrosal sinus connects the cavernous sinus with the sigmoid sinus. The straight sinus (choice E) is at the intersection of the falx cerebri and the falx cerebelli in the posterior cranial fossa. The straight sinus connects the inferior sagittal sinus with the confluence of sinuses.

Answer 4

The correct answer is B. The median nerve supplies the surface of the lateral palm, the palmar surface of the first three digits, and the distal dorsal surface of the index and middle fingers (including the nail beds). Therefore, prior to performing surgery in this area, it is essential to anesthetize a branch of this nerve (possibly a proper digital branch) to eliminate pain sensation around the nail bed of the index finger. The median nerve of the branchial plexus distributes to the flexor muscles on the forearm (flexor carpi radialis and palmaris longus), the pronators (p. quadratus and p. teres), digital flexors, and skin over the lateral surface of the hand. Neither the anterior interosseus (choice A) nor the musculocutaneous (choice C) nerves supplies the hand. The anterior interosseous nerve supplies the flexor pollicis longus, the lateral half of flexor digitorum profundus, and pronator quadratus. The musculocutaneous nerve supplies the coracobrachialis, biceps, and most of the brachialis muscle, then becomes the lateral cutaneous nerve of the forearm. The radial nerve (choice D) supplies skin on the radial side of the dorsal surface of the hand, but not the fingertips. The ulnar nerve (choice E) supplies the palmar and dorsal surfaces of the medial hand, including the palmar and dorsal surfaces of the fourth and fifth digits.

Answer 5

The correct answer is D.The products of the adrenal medulla are epinephrine (adrenalin) and norepinephrine (noradrenalin). The pathway of production of these compunds is a s follows: tyrosine to DOPA to dopamine to norepinephrine to epinephrine. The hormone secreted by alpha cells of the pancreas is glucagon, while beta cells secrete insulin. Both are peptide hormones. The adrenal cortex secretes a variety of hormones including cortisol and aldosterone, both steroid hormones. The testes secrete testosterone, also a steroid hormone.

Answer 6

The correct answer is D. During the fourth week of development, the lateral body folds move ventrally and fuse in the midline to form the anterior body wall. Incomplete fusion results in a defect that allows abdominal viscera to protrude from the abdominal cavity, a condition known as gastroschisis. 14 During development, the midgut normally herniates into the umbilical cord and then subsequently retracts into the abdominal cavity. Failure of the intestinal loop to retract from the umbilical cord (choice A) results in omphalocele. Failure of the yolk stalk to degenerate (choice B) results in an ileal (Meckel's) diverticulum or a vitelline fistula or cyst. In the early embryo, the gut tube is connected to the yolk sac by a narrow connection known as the yolk stalk. Normally, this connection degenerates. During development, certain peritoneal organs fuse with the posterior abdominal wall to become secondarily retroperitoneal. Failure of this peritoneal fusion (choice C) will result in certain organs that are normally immobile being mobile (e.g., mobile cecum). Umbilical herniation (choice E) results from abdominal viscera protruding through a weakness in the abdominal wall after development. Such protrusions are covered by subcutaneous fascia and skin, distinguishing them from gastroschisis.

Answer 7

The correct answer is C. The oculomotor nerve innervates the levator palpebrae superioris, which elevates the eyelid. This nerve also innervates the inferior oblique muscles, as well as the superior, inferior, and medial rectus muscles. The oculomotor nerve also contains preganglionic parasympathetic fibers that synapse, in the ciliary ganglion, on postganglionic parasympathetic nerve fibers that innervate the sphincter pupillae muscle, which constricts the pupil. A lesion of the oculomotor nerve may therefore result in both drooping of the eyelid (ptosis) and dilation of the pupil (mydriasis). The cervical sympathetic chain (choice A) contains preganglionic sympathetic nerve fibers, arising from the upper thoracic spinal cord, which ascend to the cervical sympathetic ganglia. A lesion of these nerves may result in Horner's syndrome, which includes a ptosis and miosis (pupillary constriction) and, often, anhidrosis (lack of sweating). The facial nerve (choice B) innervates the muscles of facial expression, including the orbicularis oculi muscle. A lesion of this nerve may therefore result in the inability to close the eye. The superior cervical ganglion (choice D) contains the cell bodies of postganglionic sympathetic nerves that innervate structures in the head. A lesion of this structure will cause Horner's syndrome. The trigeminal nerve (choice E) provides sensory innervation to much of the head. A lesion of this nerve may interfere with the corneal blink reflex.

Answer 8

The correct answer is B. The seventh intercostal nerve (the anterior ramus of the seventh thoracic spinal nerve) innervates the seventh rib. After passing through the intervertebral foramen between the seventh and eighth thoracic vertebrae, the nerve lies in the seventh intercostal space. After passing the angle of the rib, it occupies a position along the lower border of the rib, in the costal groove. Use of a local anesthetic at this point will anesthetize the rib. By the time the intercostal nerve has reached the midclavicular line (choice A), it has already innervated most of the rib. Use of an anesthetic at this point would not be effective. While the intercostal nerve is in the intercostal space medial to the angle of the rib (choice C), it is not along the lower border of the rib. The intercostal nerve does not lie along the upper border of the rib (choices D and E). Thus, injection at these sites would not be effective.

Answer 9

The correct answer is A. The uncus, which is the medial protrusion of the parahippocampal gyrus, is an external structure seen on the ventral surface of the temporal lobe. The amygdala is a collection of nuclei that lies directly beneath the uncus. The caudate nucleus (choice B) is a deep nuclear structure that lies lateral to the lateral ventricles. The claustrum (choice C) is a thin and elongated nucleus that lies just medial to the insular cortex. The hippocampus (choice D) is a nuclear structure that lies in the interior of the parahippocampal gyrus. The putamen (choice E) is a nuclear structure that resides lateral to the caudate and medial to the claustrum.

Answer 10

The correct answer is B. Aspiration pneumonia is a common complication observed in nursing home patients. The most probable site of the pneumonia can be anticipated by knowing the anatomy of the bronchial tree because the aspirated fluid usually flows downhill. In a supine or nearly supine patient, 16 the fluid flows into the trachea and then into either of the (typically the right) main bronchi. The first posteriorly located branch is the one leading to the apical aspect of (either) lower lobe. The lateral and posterior segments of the lower lobes are also supplied by posteriorly branching segmental bronchi. In contrast, the posterior aspects of the upper lobes are somewhat protected by an initial anteriorly directed bifurcation before their segmental bronchi arise. All other segments of the bronchial tree and their corresponding portions of lung are more anterior.

Answer 11

The correct answer is choice A.Firstly, the hormone involved is aldosterone, which acts to increase sodium resorption in the kidney. Note that aldosterone (a mineralcorticoid) and the glucocorticoids (cortisol, cortisone) are produced by the adrenal cortex, not medulla. The medulla, with a different developmental origin and cell type, produces catecholamines such as epinephrine and norepinephrine. The cortex, which is outside the medulla, is in three regions. On the outside is the Zona Glomerulosa, source of the mineralcorticoids. Inside of that is the Zona Fasiculata, which together with the innermost layer of the cortex, the Zona Reticularis, produce glucocortoids. Remember that interior to the Zona Reticularis, you will find the adrenal medulla. Also note that as a memory aid, the cortex layers from the outside in are G-F-R, like the GFR of the kidney.

Answer 12

The correct answer is E. By the third week of development, hematopoiesis begins in the blood islands of the yolk sac. Beginning at 1 month of age and continuing until 7 months of age, blood elements are also formed in the liver. Hematopoiesis occurs in the spleen and lymphatic organs between 2 and 4 months, and in the bone marrow after 4 months.

Answer 13

The correct answer is E. The spleen is a soft, friable organ with a thin capsule and is subject to injury upon trauma to the left side of the abdomen. It is located in the upper left quadrant of the abdomen, deep to the left ninth, tenth, and eleventh ribs. It is the most commonly injured organ in the abdomen. The adult spleen contains the largest number of lymphoid tissues in the human body. The descending colon (choice A) lies in a retroperitoneal position on the left side of the posterior abdominal wall. The descending colon begins at the splenic flexure immediately inferior to the spleen. The jejunum (choice B) is a peritoneal structure suspended by a long mesentery. It is located primarily in the upper left quadrant of the abdomen. Its long mesentery allows the jejunum to be highly mobile and thus is not likely to be injured by trauma to the body wall. The left adrenal gland (choice C) is a retroperitoneal structure that lies near the upper pole of the left kidney. It is embedded within fat and is thus well protected from injury. The left kidney (choice D) is a retroperitoneal structure that is well protected by fat.

Answer 14

The correct answer is D. There are two ways to answer this question. The formula method is that a tongue with muscle or nerve injury will protrude toward the side of injury, in this case the right side. This is similar to the case of the mandible protruding toward the side of injury when a lateral pterygoid is injured.The logical method is to imagine intrinsic muscles and extrinsic protruders of the tongue on the right side not receiving stimulation from innervation. In this case, only the left side protruders will operate. The tongue will protrude only on the left side, with the immobile right side acting as a stationary pivot while the tongue moves from left to right (toward the injured side).

Answer 15

The correct answer is D. When the forearm is rotated from anatomic position (palms facing forward, thumbs out) so that the palm faces posteriorly, the forearm is said to be pronated. Abduction (choice A) raises the arm to a horizontal position away from the body; adduction (choice B) is the reverse. Flexion (choice C) brings the arm or forearm forward, in front of the plane of the body. Rotation of the forearm so that the palm faces forward (i.e., into anatomic position) is referred to as supination (choice E).

Answer 16

The correct answer is C. The large bumps at the back of his tongue are circumvallate papillae. These are large circular structures surrounded by moat-like depressions. The lateral surfaces of these papillae contain taste buds. There are also small serous-only salivary glands in these papillae. Aphthous ulcers (choice A) are small, white, or red mouth lesions. Candidal colonies (choice B) appear in thrush, which occurs more commonly in the immunocompromised host or in those taking antibacterial drugs. You are told that the patient is healthy and not taking medications, making this condition unlikely. Filiform papillae (choice D) are the most numerous papillae of the tongue. They are small, elongated cones that create the tongue's rough texture. They do not contain taste buds. Fungiform papillae (choice E) are mushroom-shaped structures scattered among the filiform papillae. They frequently contain taste buds. They are intermediate in size between filiform and circumvallate papillae.

Answer 17

The correct answer is E. The path of the psoas major lies in the retroperitoneum and comes close to the appendix. Acute appendicitis can cause either infection or a sympathetic inflammation of the psoas. This produces clinically a "positive psoas sign," in which attempts to straighten the patient's 19 flexed (to relieve pain) hip produce sometimes marked exacerbation of the pain. None of the other muscles listed pass near the appendix.

Answer 18

``` The correct answer is C. The urachus is a fibrous remnant that extends from the umbilicus to the urinary bladder. It is also known as the median umbilical ligament of the anterior abdominal wall. The cloaca (choice A) is the primitive, endoderm-lined region that receives the terminal portion of the hindgut. It is later subdivided into urogenital and anal areas. The medial umbilical ligament (choice B) is a paired structure located deep to the peritoneum of the anterior abdominal wall. It is formed by the obliterated umbilical artery. The ureter (choice D) is the muscular tube that conveys urine from the kidney to the urinary bladder. The urethra (choice E) is the passageway that carries urine from the bladder to the perineum. ```

Answer 19

The correct answer is D. The smooth part of the right atrium (the sinus venarum) is derived from the sinus venosus. The coronary sinus and the oblique vein of the left atrium also derive from the sinus venosus. The bulbus cordis (choice A) gives rise to the smooth part of the right ventricle (conus arteriosus) and the smooth part of the left ventricle (aortic vestibule). The primitive atrium (choice B) gives rise to the trabeculated part of the right and left atria. The primitive ventricle (choice C) gives rise to the trabeculated part of the right and left ventricles. The truncus arteriosus (choice E) gives rise to the proximal part of the aorta and the proximal part of the pulmonary artery.

Answer 20

The correct answer is E. The ring described is the zona pellucida, which surrounds the ovum. The zona pellucida is rich in polysaccharides and glycoproteins and consequently stains brightly pink or red with PAS stain. Binding of the sperm cell membrane to the zona pellucida triggers the acrosome reaction, during which acrosomal enzymes are released that digest the zona pellucida, allowing the spermatozoon to contact and fuse with the ovum cell membrane. Anatomically, as layers of granulosa cells develop around the primary oocyte, microvilli from the surrounding granulosa cells intermingle with cells of the primary oocyte. The microvilli are surrounded by a layer of glycoproteins, and the entire region is called the zona pellucida. The follicular cells immediately outside the zona pellucida form the corona radiata (choice A). The larger cumulus oophorus (choice B) is the hill of follicular cells that surrounds the ovum. The theca interna (choice D) and externa (choice C) are formed from the connective tissue surrounding the follicle.

Answer 21

The correct answer is D. The spinal accessory nerve crosses the posterior triangle of the neck immediately deep to the investing fascia of the neck. This nerve innervates the trapezius muscle, which is responsible for upward rotation and elevation of the scapula. A lesion of this nerve in the posterior triangle leads to paralysis of the trapezius. Without the ability to upwardly rotate the scapula, abduction and flexion of the arm above the horizontal plane is not possible. Also, shrugging of the shoulder is impaired with paralysis of the trapezius muscle. The axillary nerve (choice A) does not pass through the neck. It is a branch of the brachial plexus, and it leaves the axilla to innervate the deltoid and teres minor muscles. The great auricular nerve (choice B) and transverse cervical nerve (choice E) are branches of the cervical plexus, which provide cutaneous innervation to the skin of the neck. No muscles are innervated by these nerves. The greater occipital nerve (choice C) is the dorsal ramus of the second cervical spinal nerve. It provides cutaneous innervation to the skin of the back of the head. No muscles are innervated by this nerve.

Answer 22

The correct answer is A. This question requires knowledge of pathophysiology with a basic understanding of anatomy. The cavernous sinuses are located on either side of the body of the sphenoid bone and become a potential route of infection because they receive blood both from the face (via the ophthalmic veins and sphenoparietal sinus) and from some of the cerebral veins. The spread of infection into the cavernous sinus can produce either central nervous system (CNS) infection or cavernous sinus thrombosis, both of which are potentially fatal. The route from the face to the brain is not arterial (choices B and C). The superior sagittal sinus (choice D) is located in the falx cerebri and drains venous blood from the brain to other dural sinuses, from which it eventually drains into the jugular vein. Zygomycosis does not reach the brain by way of the superior sagittal sinus. The superior vena cava (choice E) drains blood from the upper part of the body into the heart.

Answer 23

The correct answer is A. The recurrent laryngeal nerve is a branch of the vagus nerve, which innervates all of the intrinsic laryngeal muscles, except for the cricothyroid muscle. The cricothyroid is attached to the cricoid cartilage and the thyroid cartilage; contraction of this muscle tends to stretch and adduct the vocal ligament. The cricothyroid is innervated by the external laryngeal nerve. The lateral cricoarytenoid muscle (choice B) is innervated by the recurrent laryngeal nerve and is attached to the cricoid cartilage and the arytenoid cartilage. Its contraction causes adduction of the vocal ligament. The posterior cricoarytenoid muscle (choice C) is innervated by the recurrent laryngeal nerve and is attached to the cricoid cartilage and the arytenoid cartilage. Its contraction causes abduction of the vocal ligament. The thyroarytenoid muscle (choice D) is innervated by the recurrent laryngeal nerve and is attached to the thyroid cartilage and the arytenoid cartilage. Its contraction causes slackening of the vocal ligament. The vocalis muscle (choice E) is the most medial part of the thyroarytenoid muscle. It attaches to either the thyroid cartilage and the vocal ligament, or the arytenoid cartilage and the vocal ligament. It is innervated by the recurrent laryngeal nerve. Its contraction causes tension on segments of the vocal ligament.

Answer 24

The correct answer is A. Compression of the facial nerve within the facial canal may result in facial palsy (Bell's palsy). Because the muscles on one side of the face are paralyzed, the face appears asymmetrical. The buccinator muscle, which is located within the cheek and is innervated by the facial nerve, functions to hold food against the teeth while it is being chewed. Paralysis of this muscle can result in food and saliva accumulating between the teeth and the cheek. The buccinator originates from the alveolar processes of the maxilla and mandible. It inserts into the fibers of the obicularis oris. The masseter and temporalis muscles (choices B and E) are innervated by the mandibular division of the trigeminal nerve. These muscles of mastication function to elevate the mandible. The palatoglossus (choice C) and palatopharyngeus (choice D) muscles are innervated by the vagus nerve. The palatoglossus, with its mucosal covering, forms the palatoglossal fold (anterior pillar of the fauces), immediately anterior to the palatine tonsil. This muscle functions to draw the tongue and soft palate closer together, as occurs during swallowing. The palatopharyngeus, with its mucosal covering, forms the palatopharyngeal fold (posterior pillar of the fauces), which is immediately posterior to the palatine tonsil. This muscle causes elevation of the pharynx, as occurs during swallowing.

Answer 25

The correct answer is D. The medical condition is Barrett's esophagus, in which the normally nonkeratinizing squamous epithelium (choice E) of the esophagus undergoes metaplasia to gastric or intestinal-like epithelium composed of nonciliated columnar epithelial cells. Barrett's esophagus typically develops in the setting of chronic gastroesophageal reflux and significantly increases the risk of later development of adenocarcinoma of the distal esophagus. Ciliated columnar epithelium (choice A) is found in the respiratory tract. Cuboidal epithelium (choice B) is found in the kidney, peritoneal lining, and pleural lining. Keratinizing squamous epithelium (choice C) is found in skin. Nonkeratinizing squamous epithelium (choice E), in addition to being the normal epithelium of the esophagus, is found in mouth, nose, and vagina.

Answer 26

The correct answer is E. The superior pancreaticoduodenal artery is a branch of the gastroduodenal artery, which is a branch of the common hepatic artery, itself a branch of the celiac trunk. The inferior pancreaticoduodenal artery is a branch of the superior mesenteric artery. Occlusion of the celiac trunk would allow blood from the superior mesenteric artery to reach the branches of the celiac trunk via the connections between the superior and inferior pancreaticoduodenal arteries. The left gastric and right gastric arteries (choice A) both receive their blood from the celiac trunk. The left gastric artery is a direct branch of the celiac trunk. The right gastric artery is usually a branch of the proper hepatic artery, which is a branch of the common hepatic artery (a branch of the celiac trunk). The left and right gastroepiploic arteries (choice B) both receive their blood supply from the celiac trunk. The left gastroepiploic artery is a branch of the splenic artery, which is a branch of the celiac trunk. The right gastroepiploic artery is a branch of the gastroduodenal artery, which is a branch of the common hepatic artery (a branch of the celiac trunk). The proper hepatic and gastroduodenal arteries (choice C) are branches of the common hepatic artery, which is a branch of the celiac trunk. The right colic and middle colic arteries (choice D) are both branches of the superior mesenteric artery.

Answer 27

The correct answer is B. Hearing is the detection of sound, which consists of pressure waves conducted through air or water. The receptors of the cochlear duct provide us with a sense of hearing that allows us to detect the quietest whisper and yet remain functional in a crowded, noisy environment. The organ of Corti contains hair cells from the cochlear branch of the vestibulocochlear nerve (CN VIII). These cells rest on the basilar membrane (choice A), which separates the scala tympani (choice D) from the scala media. The hair cells are embedded in the tectorial membrane, and movement of the basilar membrane below the cells causes the hairs to bend, which generates action potentials. The tectorial membrane that lies on the hair cells does not form a boundary between the different scala; the membrane separating the scala media from the scala vestibuli (choice E) is Reissner's (vestibular) membrane (choice C).

Answer 28

The correct answer is A. The spinal cord arises from the caudal end of the neural tube. During development, an alar and a basal plate is formed, separated by a longitudinal groove called the sulcus limitans (choice E). The alar plate forms the dorsal (posterior) part of the spinal cord and becomes the sensory or afferent portion of the cord. The basal plate (choiceB) is the ventral (anterior) part of the cord and becomes the motor, or efferent, portion of the spinal cord and therefore would contain anterior horn cells. The neural crest (choice C) develops into multipolar ganglion cells of autonomic ganglia, pseudounipolar cells of spinal and cranial nerve ganglia, leptomeningeal cells, Schwann cells, melanocytes, chromaffin cells of the adrenal medulla, and odontoblasts. The brain forms from the rostral end of the neural tube (choice D).

Answer 29

The correct answer is D. The paired umbilical arteries arise from the iliac arteries. They supply unoxygenated fetal blood to the placenta. The single umbilical vein takes the newly oxygenated fetal blood from the placenta to the liver and then to the inferior vena cava via the ductus venosus. Near the level of vertebra L4, the terminal segment of the abdominal aorta divides to form the right and left common iliac arteries. These arteries carry blood to the pelvis and lower limbs. As these arteries travel along the inner surface, they descend behind the cecum and sigmoid colon, where each divides to form the internal iliac artery and external iliac artery.

Answer 30

The correct answer is E. The thyroglossal duct develops as an evagination of the floor of the pharynx in the region where the tongue develops. The adult foramen cecum of the tongue marks the site of this evagination. The distal end of this duct normally forms the thyroid gland; the proximal part of the duct normally degenerates. Failure of a part of the duct to degenerate may lead to a thyroglossal duct cyst or a median cervical cyst, as seen in this patient. The first pharyngeal cleft (choice A) forms the external ear canal. This cleft normally remains patent. The first pharyngeal pouch (choice B) forms the middle ear cavity and the auditory tube. This pouch normally remains patent. The second pharyngeal cleft (choice C) normally does not remain patent. It is typically covered over by the overgrowth of the second pharyngeal arch. If part of this pouch does remain patent, it may form a lateral cervical cyst, which is seen on the lateral side of the neck along the anterior border of the sternocleidomastoid muscle. The second pharyngeal pouch (choice D) forms the tonsillar fossa of the pharynx. The pharyngeal mucosa in this area arises from the endoderm of the pouch. Ingrowth of mesoderm cells results in the formation of the palatine tonsil.

Answer 31

The correct answer is C. Striated (skeletal) muscle not under voluntary control is an unusual feature of the upper and middle thirds of the esophagus. The middle third of the esophagus contains roughly half striated and half smooth muscle; the lower third contains only smooth muscle. All the other structures listed in the answer choices contain smooth muscle. As a side note, cardiac muscle cells do not rely on nerve activity to start a contraction. Instead, specialized pacemaker cells establish a regular rate of contraction. Because these pacemaker cells regulate the heart and the central nervous system does not, cardiac muscle is also considered striated, involuntary muscle.

Answer 32

The correct answer is D. The right gastroepiploic artery, off the gastroduodenal artery, supplies the right half of the greater curvature of the stomach and could be directly affected by ulceration of the greater curvature of the stomach at a site this close (4 cm) to the pyloric sphincter. The left gastric artery (choice A), off the celiac trunk, supplies the left half of the lesser curvature of the stomach. The left gastroepiploic artery (choice B), off the splenic artery, supplies the left half of the greater curvature of the stomach. Although it anastomoses with the right gastroepiploic artery, it is unlikely that this artery would be directly damaged by ulceration of the stomach near the pyloric sphincter. The right gastric artery (choice C), off the proper hepatic artery, supplies the right half of the lesser curvature of the stomach. The short gastric artery (choice E), actually one of several (4 to 5) short gastric arteries, off the splenic artery (occasionally the left gastroepiploic), supplies the fundus of the stomach, which is the most distant from the pylorus.

Answer 33

The correct answer is B. Cranial nerve IX is the glossopharyngeal nerve, which has a nucleus in the medulla and is necessary for the gag reflex. The gag reflex is elicited by touching either side of the posterior pharynx with a tongue blade, producing bilateral elevation of the palate and bilateral contraction of the pharyngeal muscles. The afferent of this reflex arc consists of the ipsilateral glossopharyngeal nerve, while the vagus nerve, bilaterally, supplies the efferent limb. Although the glossopharyngeal nerve may seem to be one of the less important cranial nerves, you should remember to test for its function, as a loss of gag reflex can lead to the patient's death secondary to an aspiration pneumonia. The glossopharyngeal nerve is a mixed sensory and motor nerve to the head and neck. It originates from the posterior 1/3 of the tongue, pharynx, palate, and carotid arteries of the neck. Its destination includes sensory nuclei of the medulla oblongata, as well as the pharyngeal muscles involved in swallowing. Cranial nerve VII (choice A) is the facial nerve, which supplies motor function to the face, but it does not supply the oropharynx. Cranial nerve XII (choice C) is the hypoglossal nerve, which supplies the intrinsic and most extrinsic muscles of the tongue. It is not involved in the gag reflex. Cranial nerve XI (choice D) is the spinal accessory nerve, which supplies the trapezius and sternocleidomastoid. Cranial nerve VIII (choice E) is the vestibulocochlear nerve, responsible for hearing and equilibrium.

Answer 34

The correct answer is C. Laryngeal cartilages are derived from neural crest. The larynx is composed of three cartilages that form the "body of the larynx": the thyroid cartilage, the cricoid cartilage, and the epiglottis. The larynx also contains three pairs of smaller hyaline cartilages: the arytenoid, corniculate, and cuneiform cartilages. The endothelial cells (choice A), in the simple squamous epithelium that lines the pulmonary capillaries, are derived from visceral mesoderm. The epithelial lining of primary bronchi (choice B) is derived from endoderm. Tracheal glands (choice D) and epithelium both derive from endoderm. Type I pneumocytes (choice E) are derived from endoderm.

Answer 35

The correct answer is D. The somitomeres are specialized masses of mesoderm found in the head region that give rise to the muscles of the head. The extraocular muscles are derived from somitomeres 1, 2, 3, and 5. The branchial arches (choice A) give rise to muscles of mastication (arch 1), muscles of facial expression (arch 2), and muscles of the pharynx and larynx (arches 3-6), as well as additional small muscles. The optic cup ectoderm (choice B) gives rise to the muscles of the iris (sphincter and dilator pupillae). These are the only muscles not formed from mesoderm. Somites (choice C) give rise to the inferior muscles of the neck. Splanchnic mesoderm (choice E) gives rise to smooth muscle of the viscera and the heart muscle.

Answer 36

The correct answer is A. The facial nerve and the vestibulocochlear nerves emerge from the brain stem at the cerebellopontine angle. These are the two nerves that will be initially affected by a tumor in this region. The entire anatomy of the facial nerve is as follows: the facial nerve originates from the taste receptors on the anterior 2/3 of the tongue (sensory) and from nuclei of the pons (motor). It passes through the internal acoustic canal of the temporal bone to reach the stylomastoid foramen. The glossopharyngeal and vagus nerves (choices B and E) emerge from the brain stem at the postolivary sulcus. This is caudal to the cerebellopontine angle. The optic nerve (choice C) exits from the optic chiasm on the ventral surface of the diencephalon. This is rostral to the cerebellopontine angle. The trigeminal nerve (choice D) emerges from the brain stem at the anterolateral surface of the pons. This is rostral and ventral to the cerebellopontine angle.

Answer 37

The correct answer B. The facial nerve innervates the muscles of facial expression. The visceral motor portion innervates the lacrimal gland and nasal mucous glands via the sphenopalatine ganglion. The submandibular and sublingual salivary glands are innervated via the submandiublar ganglion. This patient has a lesion of the facial nerve (VII), which leads to an inability to close the ipsilateral eye because of damaged motor fibers to the orbicularis oculi. This patient would also lose her corneal reflex on that side because of an inability to blink and would have ipsilateral paralysis of the muscles of facial expression distal to the lesion. If the lesion affected the facial nerve more proximally, additional findings would be hyperacusis (increased sensitivity to sound because of stapedius muscle paralysis), lack of taste sensation in the anterior two-thirds of the tongue, and disturbed lacrimation and salivation. Blurred vision (choice A) could occur with lesions of the oculomotor (CN III), abducens (CN VI), or trochlear (CN IV) nerves, which innervate the extraocular muscles. CN III innervates the medial rectus, inferior rectus, superior rectus, and inferior oblique muscles. CN VI innervates the lateral rectus and CN IV innervates the superior oblique. An inability to chew (choice C) would probably be the result of a lesion of the trigeminal nerve (CN V). Motor fibers of CN V innervate the muscles of mastication (temporalis, masseter, and medial and lateral pterygoid muscles), and a lesion of these fibers may cause the jaw to deviate to the side of the weak muscles. An inability to feel the face (choice D) would also be the result of a CN V lesion. This lesion could result in the ipsilateral loss of general sensation of the face and also of the mucous membranes of the oral and nasal cavities. A lesion of the accessory nerve (CN XI) would cause paralysis of the trapezius muscle, which results in a sagging of the shoulder and a weakness in attempting to shrug the shoulder (choice E).

Answer 38

The correct answer is C. The middle meningeal artery is in the interior of the lateral portion of the cranial cavity, embedded in the periosteal (outer) layer of the dura. A tear of this artery results in blood entering the potential space between the outer dural layer and the skull (epidural space), causing an epidural hematoma. The anterior cerebral artery and middle cerebral artery (choices A and B) lie on the surface of the brain. The anterior cerebral arteries supply the medial surface of the cerebral hemispheres, and the middle cerebral arteries supply the lateral surface of the cerebral hemispheres. A tear of either of these arteries would result in blood entering the subarachnoid space (subarachnoid hemorrhage). The superficial temporal artery (choice D) is a branch of the external carotid artery and is external to the skull. This artery supplies the skin and other tissue of the temple region. The superior cerebral veins (choice E) drain the cerebral hemisphere and enter the superior sagittal sinus. A tear of these veins results in blood entering the potential space between the dura and arachnoid (subdural space), causing a subdural hematoma.

Answer 39

The correct answer is B. The epiphyseal plate of the bone contains cartilage that is radiolucent. The plate in a bone that is not yet fully ossified can produce a "line" crossing the bone near the end. This may be easily mistaken for a fracture by the inexperienced. Anatomically, the epiphyseal plate separates the epiphysis from the diaphysis. Articular cartilage (choice A) is radiolucent, but occurs at the very tip of the long bones. Perichondrium (choice C) is usually difficult to see on x-ray. Primary (choice D) and secondary (choice E) ossification centers are radiopaque.

Answer 40

The correct answer is C. The mesoderm gives rise to the adrenal cortex. In addition, it also gives rise to connective tissue, cartilage, bone, muscle, blood and lymph vessels, kidneys, gonads, serous membranes lining body cavities, and the spleen. The ectoderm (choice A) gives rise to the central nervous system, peripheral nervous system, epidermis and its appendages, mammary glands, pituitary gland, tooth enamel, and the neural crest. The endoderm (choice B) gives rise to the parenchyma of the tonsils, thyroid and parathyroid glands, thymus, liver, pancreas, the epithelial lining of the gastrointestinal and respiratory tracts, urinary bladder, urethra, and auditory tube. The mesonephros (choice D) functions as an interim kidney in the embryo. The neural crest cells (choice E) give rise to cells of the spinal and cranial nerves, autonomic ganglia, melanocytes, leptomeninges, connective tissue and bone of branchial arch origin, and the adrenal medulla.

Answer 41

``` The correct answer is choice A. This is a basic histological question of a type found commonly on NBDE, which asks about basic cellular organelles and structures. The sperm cell flagellum is notable for a “9+2” arrangement of fibers formed from microtubules. The 9 single fibers form a circular ring in cross section around the 2 doubled fibers in the center. One of the significant facts about the fibers is that they are composed of microtubules, made up of tubulin. The other significant fact is that all eucaryotic flagella and cilia have this same structure (for example, cilia form the tracheal lining). Note that procaryotic (bacterial) flagellea do NOT share this structure. ```

Answer 42

The correct answer is A. The left atrium forms most of the posterior wall of the heart. The esophagus passes immediately posterior to the heart. Enlargement of the left atrium may compress the esophagus and cause dysphagia. Anatomically, the esophagus begins posterior to the cricoid cartilage, at the level of vertebrum C6. From this point, it descends toward the thoracic cavity posterior to the trachea, passes inferiorly along the dorsal wall of the mediastinum, and enters the abdominopelvic cavity through an opening in the diaphragm, the diaphragmatic hiatus. The left ventricle (choice B) forms most of the left border of the heart and most of the diaphragmatic surface of the heart. The left ventricle is not related to the esophagus. The pulmonary trunk (choice C) emerges from the right ventricle on the anterior surface of the heart. The pulmonary trunk is not related to the esophagus. The right atrium (choice D) forms the right border of the heart. It is not related to the esophagus. The right ventricle (choice E) forms most of the anterior wall of the heart and a small portion of the diaphragmatic surface of the heart. It is not related to the esophagus.

Answer 43

The correct answer is D. The sublingual salivary glands are located beneath the mucous membrane of the floor of the mouth. Numerous sublingual ducts open along either side of the lingual frenulum. Salivary glands can contain predominantly serous cells, predominantly mucous cells, or both in their acini. As you proceed from the midline laterally, acini in the sublingual gland are almost pure mucous cells, whereas acini in the submandibular gland (choice E) contain a mixture of serous and mucous cells. Acini in the parotid gland (choice C) are mostly pure serous cells. 30 The esophageal mucosa (choice A) and the oral mucosa (choice B) are squamous epithelia that do not form acini.

Answer 44

The correct answer is B. The major source of blood supply to the nasal mucosa is the sphenopalatine artery, which is the terminal branch of the maxillary artery. The sphenopalatine artery enters the nasal cavity from the pterygopalatine fossa by passing through the sphenopalatine foramen in the lateral wall of the nasal cavity. The facial artery (choice A) is a direct branch of the external carotid artery. It provides most of the blood supply to the superficial face. The superficial temporal artery (choice C) is a terminal branch of the external carotid artery. The other terminal branch is the maxillary artery. The superficial temporal artery provides blood supply to the temporal region and the lateral portion of the scalp. The superior labial artery (choice D) is a branch of the facial artery. The superior labial artery provides blood supply to the upper lip. It has a septal branch that provides some of the blood supply to the anterior portion of the septal mucosa of the nasal cavity. However, this is not the major blood supply to the nasal cavity. The transverse facial artery (choice E) is a branch of the superficial temporal artery. It provides blood supply to the parotid gland, the parotid duct, and the skin of the lateral face.

Answer 45

The correct answer is B. This question is essentially asking "which of the following nerves innervates the tip of the tongue?" The innervation of the tongue is complex. The mandibular division of the trigeminal nerve (V3) carries general somatic sensation from the anterior two-thirds of the tongue. The mandibular branch is also a sensory nerve for the lower gingiva, teeth, and lips, as well as the palate. The maxillary division (V2, choice A) carries somatic sensation from the palate, upper gingiva, and upper lip, as well as the lower eyelid, cheek, nose, and a portion of the pharynx. The facial nerve (VII, choice C) carries taste from the anterior two-thirds of the tongue, as well as innervating the lacrimal gland and the submandibular and sublingual salivary glands. 31 The glossopharyngeal nerve (IX, choice D) carries sensation and taste from the posterior one-third of the tongue. The vagus nerve (X, choice E) carries sensation from the lower pharynx.

Answer 46

The correct answer is B. The thyroid gland originates as a mass of endodermal tissue near the foramen cecum, which is near the tuberculum impar (which becomes the central part of the tongue). During development, the thyroid descends in front of the pharynx, maintaining a connection to the tongue via the thyroglossal duct. Usually, the thyroglossal duct disappears. Uncommonly, residual ectopic thyroid tissue can be left anywhere along the path, including at the back of the tongue. (In rare cases, all of the thyroid tissue remains at this site, forming a mass that should not be excised, for obvious reasons!) Anatomically, the thyroid gland curves across the anterior surface of the trachea just below the thyroid cartilage that forms the majority of the anterior surface of the larynx. The two lobes of the thyroid gland are united by a slender connection, the isthmus. The first pharyngeal pouch (choice A) develops into the middle ear and eustachian tube.The nasolacrimal ducts (choice C) connect the eyes to the oropharynx. The second pharyngeal arch (choice D) develops into many muscles of the face and the styloid process of the temporal bone. The third pharyngeal pouch (choice E) develops into the thymus and inferior parathyroid glands.

Answer 47

The correct answer is A. The superior laryngeal artery is a branch of the superior thyroid artery. It enters the larynx by passing through the cricothyroid membrane. In this region, it is accompanied by the internal branch of the superior laryngeal nerve. This nerve provides sensory innervation to the laryngeal mucosa above the vocal folds. The laryngeal mucosa below the vocal folds (choice B) receives its sensory innervation from the recurrent laryngeal nerve. The pharyngeal mucosa (choice C) receives its sensory innervation from the glossopharyngeal nerve. The cricothyroid muscle (choice D) receives its motor innervation from the external branch of the superior laryngeal nerve. The lateral cricoarytenoid muscle (choice E) receives its motor innervation from the recurrent laryngeal nerve.

Answer 48

The correct answer is C. The septum primum (first interatrial septum) develops by growing from the cranial end of the embryonic atrium toward the endocardial cushions. The gap that exists between the two atria during this period is the ostium primum. As the septum primum continues its growth, the ostium primum gets smaller until it is closed when the septum primum completes its growth and completely fuses with the endocardial cushions. Failure of the septum primum to fuse completely with the endocardial cushions leaves a persistent ostium primum, known as a primum-type atrial septal defect. The ostium primum does not form within the septum primum (choice A). The ostium primum is the communication between the two atria that exists during the formation of the septum primum. That is, the ostium primum is the space within the developing atrium not yet occupied by the septum primum. The ostium secundum normally forms within the septum primum (choice B) before the ostium primum closes by fusion of the septum primum with the endocardial cushions. Failure of the ostium secundum to form would result in embryonic death because there would be no pathway for blood to pass from the right atrium to the left atrium when the ostium primum closes, thus depriving the embryo of oxygenated blood. Most of the septum primum normally disappears. The part that remains forms the valve of the foramen ovale. This part of the septum primum normally does not fuse with the septum secundum (choice D) during prenatal life. After birth, the valve of the foramen ovale is pushed against the septum secundum as a result of the increased pressure in the left atrium. This achieves functional closure of the foramen ovale. Fusion does not normally occur at this time; it usually occurs later in life in most people. In some people, however, complete fusion never occurs (probe patency). The septum secundum normally does not fuse with the endocardial cushions (choice E).

Answer 49

The correct answer is E. The olfactory nerves can be damaged by head injury, severe infection, and tumors (such as meningiomas) that may compress the olfactory bulbs. Unilateral damage is often not noticed by the patient, but bilateral damage (which surprisingly can also be missed if it develops slowly) may lead to occasional bizarre errors in odor identification. The olfactory nerves are technically the neurons on the mucosal side of the cribriform plate that send processes through the plate to synapse in the olfactory bulb, which in turn sends axons to the pyriform cortex (the primary olfactory cortex). The insula (choice A) is thought to contain the primary gustatory (taste) cortex. The nucleus ambiguus (choice B) provides the special visceral efferent fibers carried by the glossopharyngeal and vagus nerves. The postcentral gyrus (choice C) contains the primary sensory cortex. The precentral gyrus (choice D) contains the primary motor cortex.

Answer 50

The correct answer is C.The fallopian tube is the only structure in the female genital tract with a ciliated columnar epithelium; the beating of the cilia helps move the egg into the uterus. This fact is also sometimes clinically helpful because dilated and deformed fallopian tubes can be microscopically distinguished from cystic ovarian tumors by the presence of the cilia. Each uterine tube is a hollow, muscular tube measuring approximately 13 cm in length. Each uterine tube is divided into three regions: the infundibulum, the ampulla, and the isthmus. The cervix (choice A) and vagina (choice E) are lined by squamous epithelium. The endometrium (choice B) is lined by columnar epithelium (although a few ciliated cells may be present). The covering of the ovary (choice D) is cuboidal epithelium, and cysts within the ovary can be lined by cuboidal or nonciliated columnar epithelium.

Answer 51

The correct answer is E. The motion described is hip abduction. The superior gluteal nerve from roots L4-S1 is responsible for hip abduction. The deep peroneal nerve (choice A) controls dorsiflexion of the foot. If you see a patient on the NBDE with "foot drop," think of damage to the deep peroneal nerve. The femoral nerve (choice B) is responsible for knee extension. The obturator nerve (choice C) is responsible for hip adduction. The hip adduction machine would provide resistance to the medial aspects of the thighs, and the individual would push his/her legs together against the machine's resistance. The sciatic nerve (choice D) controls knee flexion.

Answer 52

The correct answer is A. This question could have tricked you if you didn't catch the key words, "in the embryo." If you read the question too quickly and thought you were going to be asked to identify the structure described, you probably chose choice C (ligamentum venosum) because that is indeed the structure in question. In the embryo, however, this fibrous band is actually the ductus venosus. The ductus venosus is an embryonic vessel that allows blood to bypass the fetal liver; this prevents the depletion of oxygen and nutrient-rich blood in the hepatic sinusoids. 34 The embryonic umbilical arteries (choice D) become the medial umbilical ligaments. The embryonic umbilical vein (choice E) actually becomes the fibrous ligamentum teres (choice B). The ligamentum teres is located in the free margin of the falciform ligament.

Answer 53

The correct answer is B. The trapezius is a large muscle arising in the posterior midline from the superior nuchal line of the skull, ligamentum nuchae, and spinous processes of all of the thoracic vertebrae. The upper fibers, which are potentially damaged by wounds to the posterior and lateral neck, insert on the crest of the spine of the scapula, the medial border of the acromion, and the lateral third of the clavicle. The upper fibers serve to elevate the acromion. The lower fibers of the trapezius depress the medial end of the scapula (choice A). The sternocleidomastoids are important in extension of the head at the atlanto-occipital joint and flexion of the cervical vertebral column (choice C). The rhomboids and levator scapulae are important in raising the medial border of the scapula (choice D). Contraction of a single sternocleidomastoid muscle is important in turning of the face sideways (choice E) in the contralateral direction.

Answer 54

The correct answer is E. The sternoclavicular joint is quite strong and dislocates only with difficulty. Dislocations, particularly posterior dislocations, are occasionally seen and may be dangerous because of impingement onto the trachea, causing respiratory difficulties. The trachea is a tough flexible tube with a diameter of approximately 2.5 cm and a length of approximately 11 cm. The trachea begins anterior to the vertebra C6 in a ligamentous attachment to the cricoid cartilage and ends in the mediastinum at the level of vertebra T5. At this point, it branches to form the right and left primary bronchi. Both the aorta (choice A) and the superior vena cava (choice D) are more posterior than the trachea and are therefore less vulnerable. The esophagus (choice B) is located behind the trachea and is less vulnerable. The heart (choice C) lies below the clavicle and would not be at particular risk.

Answer 55

The correct answer is A. Astrocytes and oligodendrocytes are both derived from glioblasts, which, in turn, are derived from neuroepithelial cells. Other neuroepithelial cell derivatives include neuroblasts and ependymal cells. The astrocytes are the largest and most numerous glial cells. These cells are responsible for maintaining the blood-brain barrier, creating a three-dimensional framework for the central nervous system, performing repairs in damaged neural tissues, and controlling the interstitial environment. All the other choices are derived from neural crest cells. Other neural crest derivatives include the neurons of the parasympathetic and sympathetic ganglia (including the adrenal medulla), the dorsal root ganglia of the peripheral nervous system, the sensory ganglia of cranial nerves V, VII, IX, and X, and the leptomeninges (pia and arachnoid).

Answer 56

The correct answer is E. When the periosteum is torn during a fracture, it supplies cells that develop into osteoblasts and are the major producers of the new bone that reunites the two ends. Heterotopic ossification (bone formed outside the regular bone) can occur as a complication of fracture if some of the osteoblastic cells are misdirected into adjacent tissues. The periosteum assists in the attachment of the osteoblasts to surrounding tissues and to associated tendons and ligaments. This cellular layer functions in bone growth and participates in repair after an injury. Pre-existing cancellous bone (choice A) and compact bone (choice C) are not the major source of osteoblasts that form the new bone. Cartilage (choice B) and marrow (choice D) do not contribute to new bone formation after fracture.

Answer 57

The correct answer is B. The gastrohepatic ligament is the part of the lesser omentum that separates the greater peritoneal sac from the right portion of the lesser peritoneal sac. This portion of the lesser omentum has no significant blood vessels within it and may be incised for surgical access. The falciform ligament (choice A) is a mesenteric membrane between the liver and the anterior abdominal wall. This ligament is within the greater peritoneal sac and does not separate it from the lesser peritoneal sac. The gastrosplenic ligament (choice C) passes from the greater curvature of the stomach to the spleen. It separates the greater peritoneal sac from the left portion of the lesser peritoneal sac. Incision of this structure would be the appropriate surgical approach to gain access to the left side of the lesser peritoneal sac. The hepatoduodenal ligament (choice D) is part of the lesser omentum and separates the greater peritoneal sac from the right portion of the lesser peritoneal sac. It forms the anterior border of the epiploic foramen. However, the hepatoduodenal ligament contains the common bile duct, the proper hepatic artery, and the portal vein, and therefore may not be incised for surgical access. The splenorenal ligament (choice E) passes from the spleen to the parietal peritoneum on the anterior surface of the left kidney. It separates the greater peritoneal sac from the left portion of the lesser peritoneal sac. This ligament contains the splenic artery, splenic vein, and the tail of the pancreas, and therefore may not be incised to gain access to the lesser peritoneal sac.

Answer 58

The correct answer is E. Two basic things about cerebellar circuitry that are well-worth knowing are that Purkinje cells of the cerebellar cortex project to the deep cerebellar nuclei and that these nuclei project out of the cerebellum. Purkinje cells are located in the second (Purkinje) cell layer of the cerebellar cortex and form inhibitory synapses on the deep cerebellar nuclei. Climbing fibers (choice A) are afferents to the cerebellum. Specifically, they originate from the medullary olivary nuclear complex, enter the cerebellum through the inferior cerebellar peduncle, and project to the deep cerebellar nuclei and the lateral cerebellar hemispheres. Golgi cell bodies (choice B) reside in the granule cell layer of the cerebellar cortex and project predominantly to the granule cells, where they form inhibitory synapses. Therefore, they reside in and project to the cerebellar cortex. Granule cells (choice C) reside in the granule cell layer of the cerebellar cortex and send their axons to the moleculary layer, where they bifurcate into parallel fibers. Granule cells, therefore, both reside in and project to the cerebellar cortex. Mossy fibers (choice D) consist of all of the afferents (except the climbing fibers) to the cerebellum. These fibers project to deep cerebellar nuclei and glomeruli in the granular layer of the cerebellar cortex.

Answer 59

``` The correct answer is A. In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull and facial and dental anomalies. This syndrome affects bones formed by intramembranous ossification. The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones. ```

Answer 60

The correct answer is A. The esophageal venous plexus, which drains into the azygos and hemiazygos veins within the thorax, has anastomoses with branches of the left gastric vein. Thus, following blockage of the portal vein, portal blood may enter the superior vena cava via the azygos system. Other important portacaval connections include the superior rectal vein with the middle and inferior rectal veins; paraumbilical veins and epigastric veins (engorgement of these vessels results in caput medusae); and the colic and splenic veins with renal veins and veins of the posterior body wall. The gonadal veins (choice B) exclusively drain the gonads (although in the female, the ovarian vein communicates with the uterovaginal plexus). These vessels have no anastomoses with portal veins. The internal iliac veins (choice C), which drain most of the pelvis and much of the inferior extremities, have no demonstrated portal anastomoses. The splenic vein (choice D) is incorrect because it's in itself a component of the portal venous system. The vesical venous plexus (choice E), which is situated well within the pelvis and drains the bladder and the prostate (or uterus and vagina) has no association with portal vessels.

Answer 61

The correct answer is C. Secretory basket cells are found in salivary gland acini and are also called myoepithelial cells. The name implies that they are epithelial cells with muscle-like contractile properties. The are found between secretory cells and the basal lamina and exert pressure on the secretory cells to release their secretions. Secretory acini themselves are composed of mucous or serous secreting cells. Intercalated duct cells are nonspecialized cuboidal epithelial cells. Striated duct cells are columnar epithelial cells with striations (stripes) of rows of mitochondria used for ATP generation for active transport.

Answer 62

The correct answer is D. There are two methods for answering this question. The formula method states that the right lateral pterygoid moves the mandible left, whereas the left lateral pterygoid moves the mandible right. The understanding method begins with the idea that the medial pterygoid is a closer (elevator). The lateral pterygoid connects to the condyle and is a protruder. If the right lateral pterygoid pulls the right condyle out while the left lateral pterygoid and condyle remain stable, the left side will act as a stationary pivot point while the right side protrudes outward and also toward the left (medially).

Answer 63

The correct answer is D. Maturation of germ cells (spermatogenesis) within the seminiferous tubules occurs in a concentric pattern, with the less mature spermatogonia near the basal lamina and the mature forms near the tubule center. Along this route the developing sperm are nurtured by sertoli cells. Spermatogonia are 2N cells and mature into larger primary spermatocytes (4N) (choice A). These mature into secondary spermatocytes (2N) (choice B), and finally into spermatids (1N) (choice C). Spermatids undergo spermiogenesis to become mature spermatozoa (choice E). Acrosomes form from the Golgi apparatus, and a flagellum forms from microtubules. Unneeded organelles are shed. The seminiferous tubules of a reproductive-age male should exhibit all stages of maturation, with mature flagellated sperm in their centers, no longer associated with sertoli cells.

Answer 64

The correct answer is E. The upper 2/3 of the esophagus contains striated muscle. It is derived from the pharyngeal arches and innervated by the vagus nerve (CN X). The lower 1/3 contains smooth muscle from splanchnic mesoderm and is innervated by the splanchnic plexus. The vagus nerve has mixed sensory and motor functions. The sensory fibers innervate the sensory nuclei and autonomic centers of the medulla oblongata. The motor fibers innervate muscles of the palate, pharynx, and respiratory and cardiovascular systems. The hypoglossal nerve (choices A and B), or CN XII, moves the tongue. The phrenic nerve (choices A and D), derived from C3, C4, and C5, innervates the muscle of the diaphragm. The glossopharyngeal nerve (choice C), or CN IX, functions in taste, swallowing, and salivation, as well as monitoring the activity of the carotid body.

Answer 65

The correct answer is C. The left adrenal vein and the left gonadal vein (either testicular or ovarian) drain into the left renal vein. The left renal vein then drains into the inferior vena cava. In contrast, the right adrenal vein and right gonadal vein drain directly into the inferior vena cava. The hemiazygos vein (choice A) receives the venous drainage from the body wall on the left side of the thorax and abdomen. No visceral organs drain directly to the azygos or hemiazygos veins. The inferior vena cava (choice B) receives the direct venous drainage from the right adrenal vein, but not the left adrenal vein. Remember, the inferior vena cava is on the right side of the abdomen. The splenic vein (choice D) receives the venous drainage from the spleen and part of the pancreas and stomach. The splenic vein is part of the portal venous system. The superior mesenteric vein (choice E) receives venous drainage from much of the intestinal tract. It is part of the portal venous system and joins with the splenic vein to form the portal vein.

Answer 66

The correct answer is B. The bulbourethral glands are paired structures located within the deep perineal pouch, embedded within the sphincter urethrae. Their ducts pass to the spongy urethra. The homologous female structures are the greater vestibular (Bartholin's) glands, which are located in the superficial perineal pouch. The bulbospongiosus muscles (choice A) lie superficial to the bulb of the penis in males and to the bulbs of the vestibule in females. The corpora cavernosa (choice C) are paired structures, consisting of cavernous erectile tissue that form a large portion of the penile shaft in males and of the body of the clitoris in females. The membranous urethra (choice D) is the portion of the urethra that passes through the urogenital diaphragm in both males and females. The perineal body (choice E) is the centrally located tendinous structure that provides attachment for perineal musculature in both males and females. It separates the urogenital area from the anal area and is an important obstetric landmark.

Answer 67

The correct answer is A. The renal arteries emerge from the abdominal aorta at about the level of the L1/L2 intervertebral disk and travel at nearly right angles to it (on the right, passing posterior to the inferior vena cava) to enter the hilum of the kidney. The celiac trunk (choice B) gives off the common hepatic, splenic, and left gastric arteries. The common iliac artery (choice C) gives off the internal and external iliac arteries. In addition, an unascended pelvic kidney may be supplied by the common iliac artery. The inferior mesenteric artery (choice D) gives off the superior rectal, sigmoid, and left colic arteries. The superior mesenteric artery (choice E) gives off the inferior pancreaticoduodenal, intestinal (ileal and jejunal), right colic, middle colic, and ileocolic arteries.

Answer 68

The correct answer is D. Only the lateral pterygoid enters the temperomandibular joint (TMJ). Its fibers join the articular disc and capsule. These fibers are from the superior head of the muscle. Fibers from the inferior head enter the bony head of the mandibular condyle. The lateral pterygoid protrudes the mandible, depresses (opens) it, and moves it left and right. None of the other muscles listed enter the TMJ. Medial pterygoid and masseter primarily elevate (close) the mandible, whereas temporalis elevates (anterior fibers) and retrudes (posterior fibers). Buccinator forms the substance of the cheek and is also a muscle of facial expression. It is not a muscle of mastication.

Answer 69

The correct answer is E. Because the right main bronchus is wider and more vertical than the left, foreign objects are more likely to be aspirated into the right main bronchus. The superior segmental bronchus of the lower lobar bronchus is the only segmental bronchus that exits from the posterior wall of the lobar bronchi. Therefore, if a patient is supine at the time of aspiration, the object is most likely to enter the superior segmental bronchus of the lower lobe. None of the segmental bronchi of the left lung (choices A and D) are likely to receive the object because the object is less likely to enter the left main bronchus. The apical segment of the right upper lobe (choice B) is not likely to receive the foreign object because of the sharp angle that the upper lobar bronchus makes with the right main bronchus and the sharp angle that the apical segmental bronchus makes with the lobar bronchus. The medial segmental bronchus of the right middle lobe (choice C) arises from the anterior wall of the right middle lobar bronchus. Therefore, when the patient is supine, the effect of gravity will tend to prevent the object from entering this segmental bronchus.

Answer 70

The correct answer is D. All three of the nerves listed innervate muscles that supply the thumb. Extension is provided by the extensors pollicis longus and brevis, which are innervated by the radial nerve. The median nerve (choices A, B, and C) supplies the thenar group, which allows the thumb to oppose, flex, abduct, and rotate. The ulnar nerve (choices E and B) supplies the adductor pollicis, which adducts the thumb.

Answer 71

The correct answer is C. The sphenopalatine artery is the terminal branch of the maxillary artery. The maxillary artery arises from the external carotid artery and then passes through the infratemporal fossa, giving off branches to structures in this region. The artery then passes through the pterygomaxillary fissure to enter the pterygopalatine fossa. The terminal branch then passes through the sphenopalatine foramen to enter the nasal cavity and supply much of the nasal mucosa, particularly in the posterior region of the nasal cavity. The external carotid artery (choice A) arises from the common carotid artery at the carotid bifurcation. The external carotid artery has eight branches that supply the head and neck region: the superior thyroid, ascending pharyngeal, occipital, lingual, facial, posterior auricular, maxillary, and superficial temporal arteries. The facial artery (choice B) arises from the external carotid artery. It provides blood supply to much of the facial region. The nasal cavity (particularly the anterior portion) receives some of its blood supply from branches of the facial artery. The ophthalmic artery (choice D) arises from the internal carotid artery immediately after the internal carotid artery emerges from the cavernous sinus. The ophthalmic artery passes through the optic canal to supply structures in the orbit. The transverse facial artery (choice E) is a branch of the superficial temporal artery. It supplies blood to structures in the upper portion of the lateral face

Answer 72

The correct answer is D. Desmosomes are specializations of the lateral surface of the cell formed from the juxtaposition of two disc-shaped structures in adjacent cells, acting much like spot welds between the two cells. Hemidesmosomes are basically desmosomes between a single cell and an extracellular matrix structure, such as a basement membrane. Adherent junctions (choice A), or zonula adherens are bandlike junctions that help attach adjacent epithelial cells to each other. Gap junctions consist of a hexagonal lattice of tubular proteins called connexons (choice B), which form channels allowing communication between cells. Tight junctions (choice E), or zonula occludens, are formed by the fusion of the outer leaflets of apposed cell membranes on the lateral cell surfaces, just beneath the apical poles. They form a barrier to permeability, or a seal around the cell.

Answer 73

The correct answer is A.There are two ways to answer this question. The formulaic method says that damage to a lateral pterygoid or the innervation to it will make the mandible deviate toward the side of the damage. A deeper understanding of the question would show that the lateral pterygoid is the primary protruder of the mandible. Contraction of both lateral pterygoids produces straight protrusion. If the left lateral pterygoid is torn, the right muscle will begin to protrude the right side, with the left side remaining stable, and acting as a stationary pivot point. As a result, the mandible will pivot out and toward the left (the side of injury). Note that damage to muscles or innervation to one side of a tongue will also produce deviation toward the injured side.

Answer 74

The correct answer is B. The four major lingual papillae types are listed in the answer. Fungiform papillae are fairly numerous, vascular, have taste buds, and are found primarily on the anterior tongue. Filiform are avasacular, without taste buds, are the most numerous, and are found in rows. Vallate are largest, usually 7-9 in number, contain taste buds, and serous salivary glands of Von Ebner. Foliate are on the lateral surface of the tongue in ridges but are usually considered rudimentary and nonfunctional in man.

Answer 75

The correct answer is B. This patient has two risk factors for sinusitis: chronic rhinitis and allergy. She probably also has aspirin allergy, which is associated with the triad of nasal polyps, asthma, and sinusitis. In maxillary sinusitis, exudate may drain into the middle meatus through an ostium in the hiatus semilunaris, which contains openings to the frontal and maxillary sinuses and anterior ethmoidal cells.The bulla ethmoidalis (choice A), also part of the middle meatus, contains an opening to the middle ethmoidal air cells. The inferior nasal meatus (choice C) receives fluid from the nasolacrimal duct, which drains tears from the medial aspect of the orbit to the nasal cavity. The sphenoethmoidal recess (choice D) is located above the superior concha and contains an opening for the sphenoid sinus. The superior nasal meatus (choice E) is located above the superior concha and contains an opening for the sphenoid sinus.

Answer 76

The correct answer is E. The spleen follows the long axes of ribs 9 to 11 and lies mostly posterior to the stomach, above the colon, and partly anterior to the kidney. It is attached to the stomach by a broad mesenterial band, the gastrosplemic ligament. Therefore, it is the most likely organ of the group to be pierced by a sharp object penetrating just above rib 10 at the posterior axillary line. Note that the pleural cavity, and possibly the lower part of the inferior lobe of the lung, would be pierced before the spleen. The ascending colon (choice A) is on the wrong side (the right) to be penetrated by a sharp instrument piercing the left side. Most of the duodenum (choice B) is positioned too far to the right to be affected by this injury. Even the third part of the duodenum, which runs from right to left, would still be out of harm's way. In addition, the duodenum lies at about levels L1 to L3, placing it too low to be 98. Which of the tongue papillae are NOT vascular? A. Fungiform B. Filiform C. Vallate D. Foliate 2H2H The correct answer is B. The four major lingual papillae types are listed in the answer. Fungiform papillae are fairly numerous, vascular, have taste buds, and are found primarily on the anterior tongue. Filiform are avasacular, without taste buds, are the most numerous, and are found in rows. Vallate are largest, usually 7-9 in number, contain taste buds, and serous salivary glands of Von Ebner. Foliate are on the lateral surface of the tongue in ridges but are usually considered rudimentary and nonfunctional in man. 44 injured in this case. The superior pole of the left kidney (choice C) is bordered by the lower part of the spleen. However, it is crossed by rib 12 and usually does not extend above rib 11. It would probably be too low and medial to be injured in this case because this penetration is at the posterior axillary line. The left lobe of the liver (choice D) is positioned just beneath the diaphragm, just over and anterior to the stomach. The anterior positioning of this structure makes it an unlikely candidate for injury in this case. Even with deep penetration at the correct angle, it would not be penetrated before the spleen.

Answer 77

The correct answer is B. Striated duct cells line sections of salivary ducts, which modify the composition of saliva. In particular, they may add potassium, remove sodium, or add bicarbonate. This ionic movement, mostly against a concentration gradient, requires energy in the form of ATP. This ATP is made in mitochondria. Rows of mitochondria in these cells, located near the base, appear in light microscopy to be stripes or striations. Mucous and serous secretory cells, because of their protein secreting function, may have highly developed ribosomes, rough endoplasmic reticulum, and golgi complexes. Intercalated duct cells have no unique specializations of note. Myoepithelial cells have contractile ability, somewhat like muscle cells.

Answer 78

The correct answer is A. Adipose tissue is loose connective tissue dominated by adipocytes. Surgeons worry about their obese patients more than their skinny ones because a thick layer of relatively poorly vascularized, subcutaneous fatty tissue is both mechanically unstable (it holds stitches poorly) and heals very slowly. These patients have a frequent rate of dehiscence (tearing open of the incision site) with subsequent, difficult-to-control infection (access by antibiotics, leukocytes, and serum antibodies are all hampered by the poor blood supply). Loose connective tissue (choice C) is well vascularized and surgeons do not usually worry much about it during the healing process. Muscle (choice D) usually heals well after surgery. Skin (choice E) usually heals well, unless it becomes infected.

Answer 79

The correct answer is D. Monozygotic twins, or identical twins, develop from a single fertilized egg that subsequently splits during either the blastomere or blastocyst stage. It is more common in the blastocyst stage at the end of the first week. This results in two inner cell masses in the same blastocyst cavity. They usually develop a common placenta and chorionic cavities but separate amniotic cavities. Splitting in the second week usually results in shared amniotic cavities as well. Conjoined twins (choice A), or Siamese twins, result from incomplete splitting of the embryo. Dizygotic twins (choice B) and fraternal twins (choice C) are the same, and are the most common type of twins. They share the same genetic relatedness as do siblings of separate pregnancies. This type of twinning occurs because of simultaneous double ovulation followed by fertilization by two sperm. They each develop their own placenta and membranes. A single gestation (choice E), and a single birth, is the result of a single fertilization without any splitting of the embryo.

Answer 80

The correct answer is B. The nerve is the axillary branch of the posterior cord (also called the axillary nerve), which can be damaged by either fracture or dislocations of the humeral neck. The muscle supplied by this nerve is the deltoid muscle. The deltoid arises from the lateral portions of the clavicle and the acromion and inserts into the deltoid tuberosity of the humerus. The deltoid arises from both the acromion (choice A) and the clavicle. The deltoid does not arise from the coracoid process (choices C, D, and E).

Answer 81

The correct answer is A. The brachial artery is immediately medial to the tendon of the biceps brachii at the elbow. As the artery enters the forearm, it is covered by the bicipital aponeurosis, a broadening of the biceps tendon. The musculocutaneous nerve (choice B) does not cross the elbow. The musculocutaneous nerve gives off all of its muscular branches to muscles in the arm. The remainder of the nerve is then renamed the lateral cutaneous nerve of the forearm, which passes the elbow lateral to the tendon of the biceps. The profunda brachii artery (choice C) arises from the brachial artery in the proximal part of the arm. It accompanies the radial artery in the musculospiral groove and then divides into the radial collateral artery and middle collateral artery, which cross the elbow lateral to the tendon of the biceps. The radial nerve (choice D) lies within the musculospiral groove along the back of the humerus, then passes between the brachioradialis muscle and the brachialis muscle at the elbow, lateral to the tendon of the biceps. The ulnar nerve (choice E) crosses the elbow posterior to the medial epicondyle of the humerus. It then passes between the two heads of the flexor carpi ulnaris and courses through the forearm deep to this muscle.

Answer 82

The correct answer is A. Because of the proximity of the axillary nerve to the glenohumeral joint, a fracture of the surgical neck of the humerus or an inferior dislocation of the humerous could damage the nerve. The axillary nerve innervates the deltoid muscle. The deltoid abducts, adducts, flexes, extends, and rotates the arm medially. The axillary nerve also innervates the teres minor, which rotates the arm laterally. The dorsal scapular nerve (choice B) innervates both the major and minor rhomboid muscles. These muscles raise the medial border of the scapula upward and laterally. The radial nerve (choice C) innervates muscles involved in the movement of the forearm and hand. The suprascapular nerve (choice D) innervates the supraspinatus and infraspinatus. The supraspinatus abducts the arm, whereas the infraspinatus rotates the arm laterally. This nerve travels along the posterior aspect of the scapula and would not easily be subjected to injury in a dislocation of the shoulder joint. The thoracodorsal nerve (choice E) innervates the latissimus dorsi, which adducts, extends, and rotates the arm medially.

Answer 83

The correct answer is D. The right ventricle forms most of the anterior wall of the heart and extends from approximately the right border of the sternum to approximately 2 inches to the left of the sternum at the level of the fourth intercostal space. The left atrium (choice A) forms the posterior wall of the heart. The only portion of the left atrium seen on the anterior surface of the heart is the left auricular appendage, which is at the level of the second intercostal space on the left. The left ventricle (choice B) forms most of the left border of the heart and the diaphragmatic surface of the heart. It forms the anterior wall of the heart in a region from approximately 2 to 3 inches from the left border of the sternum from the third to the fifth intercostal space. The right atrium (choice C) forms the right border of the heart. Its anterior surface is on the right side 55 of the sternum from approximately the third to the sixth rib. The left lung (choice E) is displaced away from the sternum on the left side by the presence of the heart.

Answer 84

The correct answer is C. While the third-week embryo is a primitive trilaminar plate, in the fourth week, the heart begins to form and begins beating almost immediately. Hematopoiesis occurs in the yolk sac, and a primitive circulatory system connects the capillary plexuses of the yolk sac and chorion to the embryo. Partitioning of the atrium also begins in the fourth week. During the fifth week, cardiac septa form and the atrioventricular (AV) cushions fuse. By the sixth week, the heart is close to fully formed. This early sequence for the heart explains why it is so difficult to try to prevent congenital malformations of the cardiovascular system from occurring because the mother of a 6- week-old fetus is only about 8 weeks from her last menstrual period and may have assumed that she just "missed a period" (a very common phenomenon) for reasons other than pregnancy.

Answer 85

The correct answer is D. This is a relatively simple question that requires you to visualize the relationship among the key parts of the kidney and to identify the one that lies most medially. Because the kidneys ultimately drain into the ureter at their medial poles, you are looking for the structure that is closest to the ureter. The correct answer is the renal pelvis. The renal pelvis is the dilated upper portion of the ureter that receives the major calyces. In terms of the other answer choices, the order from most lateral to most medial is as follows: renal cortex (choice C), renal pyramid (choice E), minor calyx (choice B), major calyx (choice A), and then renal pelvis (choice D).

Answer 86

The correct answer is D. Brunner's glands are located in the submucosa of the duodenum. These glands are connected to the intestinal lumen by ducts that open into certain crypts. They secrete an alkaline product that protects the duodenal mucosa from the acidic chyme and helps achieve optimal pH for pancreatic enzymes. Note that if you did not recall the location of Brunner's glands, the question's description of their function allowed you to deduce it on the basis of your knowledge of the anatomy of the small intestine. You should have immediately ruled out choices C and E because they are too far from the pancreas. Choices B and D would therefore remain as the best possible answers because of their proximity to the pancreas. If you remembered the structure and function of the ampulla of Vater, you were left with the correct answer. The small intestinal villi (choice A) are outgrowths of the mucosa into the lumen. Their epithelium contains columnar absorptive cells and goblet cells (which produce acid glycoproteins that protect and lubricate the lining of the intestine). Near the base of each villus are tubular glands called crypts, whose lining is continuous with the simple columnar epithelium of the villus. The crypts include Paneth cells, which produce acidophilic cytoplasmic granules containing bactericidal enzymes. The ampulla of Vater (choice B) receives bile from the common bile duct and the main pancreatic duct, delivering it to the duodenum through the major duodenal papilla. The mucosa and submucosa of the jejunem (choice C) are both included in the permanent folds called the plica circulares. The submucosa of the ileum (choice E) is the home of Peyer's patches, which are large aggregates of lymphoid nodules.

Answer 87

The correct answer is D. Injections are given in the upper, outer quadrant of the buttocks to prevent damage to the sciatic nerve, which is present in the lower quadrant. The other nerves listed are not particularly vulnerable to injections into the buttocks. The common peroneal nerve (choice A) is a branch of the sciatic nerve that diverges from it in the popliteal fossa. It then divides into the superficial and deep peroneal nerves. The lateral femoral cutaneous nerve (choice B derives from the lumbar plexus, emerges slightly below the anterior superior iliac spine, and supplies the skin of the anterior thigh down to the knee. The obturator nerve (choice C) derives from the lumbar plexus, diverges from the femoral nerve in the psoas muscle, and passes medially along the lateral pelvic wall to run in the obturator canal, where it divides into anterior and posterior divisions. The anterior division generally supplies the gracilis, adductor brevis, and adductor longus; the posterior division generally supplies the obturator externus and the adductor part of the adductor magnus. The superior gluteal nerve (choice E) is a branch of the sacral plexus. It supplies the gluteus minimus and medius and the tensor fascia lata. Small branches of this nerve are likely to be encountered in the upper outer quadrant of the buttock, but injection here is relatively safe.

Answer 88

The correct answer is C. Elevation of the tongue is carried out by the styloglossus (innervated by the hypoglossal nerve, CN XII) and the palatoglossus (innervated by the pharyngeal plexus). The palatoglossus originates on the anterior surface of the soft palate and inserts in the side of the tongue. The buccinator (choice A) functions in storing, filling, and emptying the vestibule. The geniohyoid (choice B) moves the hyoid anteriorly to open the pharynx. The palatopharyngeus (choice D) produces a "stripping wave" on the posterior pharyngeal wall. The tensor palati (choice E) tenses the soft palate.

Answer 89

The correct answer is C. The stapedius muscle is innervated by the facial nerve (cN VII). This muscle is located in the middle ear and attaches to the neck of the stapes. Contraction of the stapedius reduces the amplitude of oscillation of the stapes and thus reduces the perceived loudness of a sound. Paralysis of this muscle may result in hyperacusis. Note that the seventh nerve also innervates all muscles of facial expression. The anterior belly of the digastric muscle (choice A) is a muscle in the floor of the mouth that is innervated by the mandibular division of the trigeminal nerve. The geniohyoid muscle (choice B) is one of the suprahyoid muscles in the neck. This muscle is innervated by C1 spinal nerve fibers that travel for a short distance with the hypoglossal nerve. The stylopharyngeus muscle (choice D) is one of the longitudinal muscles of the pharynx that acts to elevate the pharynx. The masseter muscle (choice E) is one of the muscles of mastication. All of the muscles of mastication are innervated by the mandibular division of the trigeminal nerve.

Answer 90

The correct answer is E. The splenic artery passes behind the stomach and gives off the short gastric artery and the left gastroepiploic artery immediately after passing the greater curvature. The left gastroepiploic artery has a strong anastomotic connection to another arterial supply, while the short gastric does not, so the area supplied by branches of the short gastric arteries is more vulnerable to ischemia in this setting. If the block had occurred proximal to, instead of at, the branch point, the short gastric vessels could be supplied by backflow from the left gastroepiploic artery. The left gastric artery (choice A) is not supplied by the splenic artery. The left gastroepiploic artery (choice B) can be alternatively supplied by its anastomotic connection to the right gastroepiploic artery. The right gastric artery (choice C) is not supplied by the splenic artery. The right gastroepiploic artery (choice D) is normally supplied by the gastroduodenal artery.

Answer 91

The correct answer is E. The suboccipital triangle lies in the neck at the base of the skull. It is bounded by the inferior oblique, rectus major, and superior oblique muscles. The vertebral artery can be found within the suboccipital triangle, lying on the posterior arch of the atlas, lateral to the midline, typically at about the level of the lower portion of the ear lobe. Care should be taken in accessing the vessel because the first cervical nerve lies between the vertebral artery and the posterior arch of the atlas. The circle of Willis contains the following arteries: anterior communicating, anterior cerebral, posterior communicating, and posterior cerebral. The anterior triangle of the neck (choice A) is in the anterior neck and is bounded by the neck midline, the mandible, and the sternocleidomastoid muscle. The anterior triangle of the neck is subdivided into the muscular, carotid, submandibular, and submental triangles. The small muscular triangle (choice B) lies between the superior belly of the omohyoid and the 59 sternohyoid muscle. The posterior triangle of the neck (choice C) is on the side of the neck and is bounded by the sternocleidomastoid muscle, the trapezius, and the middle third of the clavicle. The submental triangle (choice D), also called the suprahyoid triangle, is found below the lower jaw and is bounded by the hyoid bone and anterior bellies of the digastric muscles.

Answer 92

The correct answer is D. The cephalic vein arises from the elbow along the anterior lateral surface of the arm. Specifically, the superficial arch empties into the cephalic vein, which ascends along the radial side of the forearm. It can be reliably found in the deltopectoral groove between the deltoid and pectoralis major. This groove lies diagonally (arising medially) below the clavicle. The cephalic vein is good for cannulation because its location is particularly constant. The cephalic vein is unrelated to the triceps, although it does pass in the arm over the biceps (choice A). The cephalic vein is not related to either the triceps or the brachialis (choice B). The cephalic vein is not related to either the coracobrachialis or the brachialis (choice C). The cephalic vein is not related to the sternocleidomastoid (choice E).

Answer 93

The correct answer is A. The pituitary gland is located in the pituitary fossa within the skull. The floor of this fossa is formed by the sella turcica. The lateral walls of the fossa are formed by the cavernous sinuses. The abducens nerve passes through the cavernous sinus along with the internal carotid artery. As the tumor expands laterally, the first nerve that will be encountered is the abducens nerve, producing a lateral rectus palsy. The abducens nerve or cranial nerve VI originates from the pons and enters the lateral rectus muscle. It is responsible for aiding in eye movements. The oculomotor nerve (choice B) lies in the lateral wall of the cavernous sinus. It is farther from the pituitary gland than is the abducens nerve. The optic nerve (choice C) is anterosuperior to the pituitary gland. Upward expansion of the tumor may compress the optic chiasm. The trigeminal nerve 60 (choice D) is found posterior to the cavernous sinus. Two of its three divisions (ophthalmic and maxillary divisions) pass through the lateral wall of the cavernous sinus and are farther from the pituitary gland than is the abducens nerve. The trochlear nerve (choice E) is also in the lateral wall of the cavernous sinus and would be affected later if the tumor continued to expand.

Answer 94

The correct answer is A. Loss of abductors and external rotators can cause an adducted and internally rotated shoulder. The biceps accomplish both of these motions. Loss of flexion and supination by the biceps muscle causes the extended, pronated elbow ("porter's tip" or "waiter's tip" position). The brachialis muscle (choice B) is a pure flexor of the elbow. The coracobrachialis muscle (choice C) functions at the elbow by helping to hold an object under the arm. The deltoid muscle (choice D) is a powerful abductor of the shoulder. The pronator teres muscle (choice E) is a powerful pronator of the elbow.

Answer 95

The correct answer is B. Most afferents to the cerebral cortex derive from the cerebral cortex. This type of extensive interconnection of cortical areas facilitates communication and integration between cortical areas on the same side or on different sides of the brain. The basal ganglia (choice A) receive their most prominent input from the cortex but output to the globus pallidus and the substantia nigra pars reticulata, rather than directly to the cerebral cortex. The hippocampus (choice C) sends most of its projections to the mammillary bodies and the thalamus via the fornix, rather than to the cerebral cortex. The ascending tracts of the spinal cord (choice D) carry sensory information to brainstem nuclei, thalamus, and cerebellum, rather than directly to the cerebral cortex. The thalamus (choice E) projects to the cerebral cortex, but the cortex receives quantitatively more fibers from other areas of cortex than from the thalamus.

Answer 96

The correct answer is A. The nerve in question is the median nerve, which lies between the palmaris longus and flexor carpi radialis tendons on the anterior aspect of the forearm. The median nerve is formed from both the lateral and medial cords of the brachial plexus. The brachial plexus innervates the shoulder girdle and upper limb with contributions from the ventral rami of spinal nerves C5 through T1. The nerves that form this plexus originate from trunks and cords named accordingly.

Answer 97

The correct answer is A. The ductus arteriosus connects the left pulmonary artery to the aortic arch. It is derived from the left sixth aortic arch. During prenatal life, the pressure gradient causes blood to flow from the left pulmonary artery to the aorta. This allows fetal blood to bypass the pulmonary system. However, after birth, the pressure gradient reverses, and if the ductus arteriosus remains patent, the flow is from the aorta to the left pulmonary artery. The ductus arteriosus does not connect to the pulmonary veins or the right pulmonary artery (choices B, C, and E). The flow through the ductus arteriosus is from the left pulmonary artery to the aorta (choice D) prior to birth, it but reverses after birth.

Answer 98

The correct answer is D. The free edge of the lesser omentum contains three important structures: the common bile duct, the hepatic artery, and the portal vein. Neither the cystic duct (choices A, B, and C) nor the hepatic vein (choices B, C, and E) lies in the free edge of the lesser omentum.

Answer 99

The correct answer is C. Questions like these are particularly amenable to the use of test-taking strategies because even if you don't know 100% of the answer, you will be able to eliminate some answer choices on the basis of knowledge you do have. For example, you probably are aware that the peritoneum does not lie above the transversus abdominis muscle, enabling you to eliminate choice A and increase your chances of answering correctly by 20%. Likewise, the external oblique must be external to the internal oblique, which eliminates choices A and D.

Answer 100

The correct answer is C. Formation of the notochord is a third week event, occurring as a relatively early part of development of the trilaminar disc. More specifically, notochord formation begins about day 16, and the neuroenteric canal forms on about day 18. Two days after conception (choice A), implantation has not yet occurred. By seven days after conception (choice B), the blastocyst has usually implanted in the endometrium. By day 28 (choice D), gastrulation has occurred, and organogenesis is under way. By day 60 (choice E), organogenesis is complete.

Answer 101

The correct answer is E. Pseudounipolar cells of spinal and cranial nerve ganglia derive from the neural crest. Other cell types that derive from the neural crest include Schwann cells, multipolar ganglion cells of autonomic ganglia, chromaffin cells of the adrenal medulla, odontoblasts, melanocytes, and cells that make up the leptomeninges (pia and arachnoid). All of the other cell types listed derive from the neural tube. Physiologically, in a unipolar or pseudounipolar neuron, the dendritic and axonal processes are continuous. The cell body lies off to one side. Sensory neurons of the peripheral nervous system are usually unipolar, and their axons may be myelinated.

Answer 102

The correct answer is E. The motor component (special visceral efferent) of the facial nerve (CN VII) exits the skull via the stylomastoid foramen, passes lateral to the styloid process, and then enters the parotid gland. Within the gland, two divisions can usually be identified (upper and lower), which in turn give off five named branches that innervate the muscles of the face. The upper division gives rise to the temporal and zygomatic branches, which collectively innervate the frontalis, corrugator, and orbicularis oculi muscles. The lower division gives off the buccal, mandibular, and cervical branches. The largest, the buccal, innervates the muscles attaching to the upper lip, including the orbicularis oris and the levators, as well as the buccinator and the muscles of the nose. The mandibular branches innervate the muscles of the lower lip and of the chin, whereas the cervical branch innervates the platysma muscle. There are usually communicating branches between the named terminal nerves so that overlapping innervation of the muscles occurs. If the lower division is injured, there will be weakness (not frank paralysis because of the innervation overlap) of the muscles that attach to the lower lip. An inability to furrow the brow (choice A) would be caused by denervation of the corrugator supercilii and frontalis muscles, which are innervated by the upper division of the facial nerve. Choice B is wrong because once the facial nerve emerges from the stylomastoid foramen, it is a pure motor nerve (special visceral efferent, or branchiomotor nerve). It carries no sensory nerve fibers. Ptosis (a drooping of the upper eyelid; choice C) is the result of a paralysis of the levator palpebrae muscle, which is innervated by the oculomotor (CN III) nerve. Choice D is not correct because the orbicularis oculi muscle is innervated by branches from the upper division of the facial nerve.

Answer 103

The correct answer is A. The lower trunk of the brachial plexus contains nerve fibers from the eighth cervical and first thoracic spinal nerves. These nerve fibers innervate the intrinsic muscles of the hand, including the interosseous muscles, responsible for abduction and adduction of the digits, and the opponens muscle, responsible for opposition of the thumb. The lower trunk ascends from the lower neck and upper thorax to reach the axilla. Upward traction on the upper limb may stretch the lower trunk and injure these nerve fibers. The median nerve (choice B) innervates many muscles of the anterior compartment of the forearm and some muscles in the hand, including the opponens muscle. The median nerve, however, does not innervate the interosseous muscles, responsible for abduction and adduction of the digits. The musculocutaneous nerve (choice C) innervates the muscle of the anterior compartment of the arm. It does not innervate any muscles in the hand. The upper trunk of the brachial plexus (choice D) contains nerve fibers from the fifth and sixth cervical spinal nerves. The nerve fibers innervate muscles in the proximal part of the upper limb, including muscles around the shoulder and axilla. No muscles in the hand are innervated by these nerve fibers. The ulnar nerve (choice E) innervates many muscles in the hand, including the interosseous muscles, which are responsible for abduction and adduction of the digits. However, it does not innervate the opponens muscle, which is responsible for opposition of the thumb.

Answer 104

The correct answer is A. The endocardial cushions form the fibrous tissue "skeleton" of the heart, which lies between the chambers of the heart. A failure of fusion of the cushions can cause an atrioventricular defect, which, in extreme cases, can make the heart behave as if it were a single chamber. Surgical correction of a large defect may be difficult and may not yield an effective heart because other malformations, such as small ventricular size, may coexist. The causes of coarctation of the aorta (choice B) are unclear but are not thought to be related to incomplete fusion of the endocardial cushions. Pulmonary stenosis (choice C) can be caused by fusion of the cusps of the semilunar valve or by unequal division of the truncus arteriosus. Tetralogy of Fallot (choice D) is caused by failure of the pulmonary trunk and aorta to line up with the ventricular openings. Transposition of the great vessels (choice E) results from abnormal migration of neural crest cells, leading to failure of spiral development of the aorticopulmonary septum.

Answer 105

The correct answer is D. The sensory innervation of the tongue is as follows: the anterior two thirds of the tongue is innervated by CN V (trigeminal) for touch sensation, and CN VII (facial) through the chorda tympani for taste sensation. CN IX (glossopharyngeal) innervates the posterior one third for touch and taste. Some texts state that the most posterior areas of the tongue may have innervation from CN X (vagus) also. The dividing line for the two thirds and one third is the row of circumvallate papillae. These papillae themselves are innervated by CN IX (glossopharyngeal).

Answer 106

The correct answer is D. The cells of the anterior pituitary can be classified as chromophils (stain with dyes) or chromophobes (do not stain with dyes). The chromophils can be further divided in acidophils (stain with acidic dyes) and basophils (stain with basic dyes). The acidophils include the somatotrophs, which secrete growth hormone, and the mammotrophs, which secrete prolactin. The basophils include the corticotrophs, which secrete ACTH (choice A), the gonadotrophs, which secrete FSH and LH (choices B and C), and the thyrotrophs, which secrete TSH (choice E).

Answer 107

The correct answer is C. The bladder is supplied by the vesicular branches of the internal iliac arteries. The internal iliacs arise from the common iliac artery. The external iliac (choice A) also arises from the common iliac artery. It makes no contribution to the blood supply of the bladder. The inferior epigastric (choice B) is a branch of the external iliac artery. It serves as a landmark in the inguinal region. The internal pudendal (choice D) is a branch of the anterior division of the internal iliac artery. It supplies the rectal area and the organs. The lateral sacral (choice E) is a branch of the posterior division of the internal iliac artery.It supplies sacral structures.

Answer 108

The correct answer is E. The mediastinum is divided into four regions. The region above the manubriosternal junction (level of fourth thoracic vertebra) is the superior mediastinum. The region below the manubriosternal junction is divided into the anterior mediastinum (anterior to the pericardium), the middle mediastinum (within the pericardium), and the posterior mediastinum (posterior to the pericardium). The thoracic duct enters the thorax through the aortic hiatus of the diaphragm. At this point it lies in the posterior mediastinum, the region posterior to the pericardium. As it ascends through the thorax and passes the level of the fourth thoracic vertebra, it enters the superior mediastinum. The anterior mediastinum (choices A and B) contains the thymus and fatty connective tissue. The middle mediastinum (choices A, C, and D) contains the heart and the roots of the great vessels. In addition to the thoracic duct, the superior mediastinum (choices B, D, and E) contains the ascending aorta, aortic arch, branches of the aortic arch, descending aorta, superior vena cava, brachiocephalic veins, thymus, trachea, and esophagus. In addition to the thoracic duct, the posterior mediastinum (choices C and E) contains the descending aorta, azygos vein, hemiazygos vein, and the esophagus.

Answer 109

The correct answer is D. The ureter passes directly inferior to the uterine artery, lateral to the body of the uterus near its junction with the cervix ("water flows under the bridge"). During a hysterectomy, therefore, the ureter (instead of the uterine artery) may be inadvertently ligated. The internal iliac artery (choice A) gives rise to the uterine artery, the primary blood supply of the uterus. The internal iliac vein (choice B) receives blood from the uterine vein (choice E), the primary venous drainage of the uterus. The ovarian artery (choice C) arises from the abdominal aorta and is the primary blood supply of the ovaries.

Answer 110

The correct answer is A. Abduction is movement away from the longitudinal axis of the body. The muscle is the abductor digiti minimi, the function of which is to abduct (separate) the toe away from the fourth toe. The abductor digiti minimi is supplied by the lateral plantar nerve. This muscle also helps act as a "spring" on the sole of the foot during walking. The key to this question is the insertion on the lateral side of the toe. Contraction on this side pulls the toe away from midline. Adduction (opposition of the toes, choice B) is supplied by the plantar interossei. Extension (choice C) is supplied by the extensor digitorum longus. Flexion is movement in the anterioral posterior plane that reduces the angle between the articulating joints. Extension occurs in the same plane but increases the angle between articulating elements. The flexor digitorum brevis flexes both the middle phalanx on the proximal phalanx (choice D) and the proximal phalanx on the metatarsal (choice E).

Answer 111

The correct answer is C. The locus coeruleus is a dense collection of neuromelanin-containing cells in the rostral pons, near the lateral edge of the floor of the fourth ventricle. The fact that it appears blue-black in unstained brain tissue gave rise to its name, which means "blue spot" in Latin. These cells, which contain norepinephrine, provide the majority of noradrenergic innervation to the forebrain, including the cerebral cortex.The basal nucleus of Meynert (choice A), a part of the substantia innominata, is a major collection of forebrain cholinergic neurons. These neurons (together with neurons in septal nuclei) innervate the neocortex, hippocampal formation, and the amygdala. The basal nucleus is one of the structures that degenerates in Alzheimer's disease.The caudate nucleus (choice B) is part of the basal ganglia, located immediately lateral to the lateral ventricles. There are at least two important cell types in the caudate. GABAergic projection neurons (the majority) innervate the globus pallidus and substantia nigra pars reticulata. The GABAergic neurons degenerate in Huntington's disease, leading to enlarged lateral ventricles that are clearly visible on MRI. The caudate also contains cholinergic interneurons, which provide most of the acetylcholine to the striatum (caudate and putamen). The balance of striatal acetylcholine and dopamine is important for the treatment of patients with extrapyramidal symptoms, sucha as Parkinson's disease or parkinsonism accompanying therapy with antipsychotic medications. The raphe nuclei (choice D) are located in the midline at most levels of the brainstem. They contain seratonergic cell bodies that innervate virtually every part of the central nervous system. The substantia nigra (choice E) is located in the midbrain and consists of the substantia nigra pars compacta and the substantia nigra pars reticulata. The substantia nigra pars compacta contains the nigrostriatal neurons that are the source of striatal dopamine. This cell degenerates in Parkinson's disease or in response to neurotoxic agents such as MPTP. The substantia nigra pars reticulata consists predominately of GABAergic neurons that innervate the thalamus.

Answer 112

The correct answer is A. The long head of the biceps tendon is vulnerable to abrasion as it moves within the bicipital grove between the greater and lesser tuberosities of the humerus. The tendon occasionally snaps, particularly in the elderly. Fortunately, the brachialis and brachioradialis are sufficiently strong flexors of the elbow in which function is retained even if no specific repair of the tendon is undertaken. The flexor carpi ulnaris and the flexor carpi radialis (choice B) are flexors at the wrist, not elbow. The flexor digitorum superficialis and the flexor digitorum profundus (choice C) are flexors of the wrist and fingers. The pronator teres and the supinator (choice D) pronate and supinate the forearm, respectively. The triceps and the coracobrachialis (choice E) extend the elbow and flex the shoulder, respectively.

Answer 113

The correct answer is A. The clinical history suggests trigeminal neuralgia, which is characterized by extreme pain along the distributions of the maxillary and mandibular subdivisions of the fifth cranial nerve, associated with a "trigger zone." The trigeminal nerve is derived from the first branchial arch. The second branchial arch (choice B) gives rise to the muscles of facial expression and is innervated by the facial nerve, cranial nerve VII. The third branchial arch (choice C) is innervated by the ninth cranial nerve, the glossopharyngeal, which innervates the stylopharyngeus muscle. The fourth branchial arch (choice D) gives rise to most pharyngeal constrictor muscles and is innervated by the tenth cranial nerve, the vagus nerve.

Answer 114

The correct answer is C. The primitive streak is the region of the epiblast through which the cells that give rise to the notochord and the mesoderm of the embryo pass. The only adult derivative of the notochord is the nucleus pulposus of the intervertebral disk. The mesoderm gives rise to many different tissue types, including muscle, connective tissue, and blood. The dorsal root ganglia (choice A) are derived from neural crest cells. The neural crest develops at the time of neurulation, which is a process of infolding of the neural ectoderm that is induced by the notochord. The lining of the gastrointestinal tract (choice B) is derived from endoderm. The endoderm also gives rise to evaginations of the gastrointestinal tract, such as the liver and pancreas. The smooth muscle and connective tissue of the gastrointestinal tract are derived from mesoderm. The spinal cord (choice D) is derived from neural ectoderm, which invaginates during neurulation to form the neural tube. The caudal part of the neural tube forms the spinal cord, and the rostral part of the neural tube forms the brain. The thyroid gland (choice E) is derived from endoderm. The endoderm of the floor of the pharynx evaginates to form the thyroglossal duct, which descends to form the thyroid gland. The adult site of the evagination of the thyroglossal duct is marked by the foramen cecum on the tongue.

Answer 115

The correct answer is E. A massive pulmonary embolus can interrupt pulmonary blood flow, producing acute cor pulmonale with abruptly developing right ventricular dilatation because the right ventricle pumps blood directly into the area of blockage, the pulmonary artery. Other parts of the heart are secondarily affected somewhat later. Acute cor pulmonale is a surgical emergency, requiring immediate correction of the underlying problem, which is usually a pulmonary embolus lodged early in the pulmonary circulation. Acute cor pulmonale is less common than chronic cor pulmonale, which is seen as a complication of many chronic lung diseases. The left main coronary artery (choice A) and right main coronary artery (choice D) would be affected secondarily to the reduced blood flow to the left heart and aorta, from which the coronary arteries arise. The left ventricle (choice B) would be affected secondarily by reduced blood flow from the pulmonary veins to the left atrium. The right atrium (choice C) would be affected after the right ventricle because it is farther from the circulatory block.

Answer 116

The correct answer is E. There are many overlapping and sometimes confusing terms for bone types. Compact bone is dense and contains Haversian systems. It is also known as lamellar (layered) bone. Spongy bone is also known as trabecular bone and does not contain Haversian systems. Compact bone is normally found on the outside surface of bones, whereas spongy bone is found on the inside. Bundle bone refers to compact bone containing collagen attachment fibers, such as those found in the alveolar bone of the periodontal ligament. Intramembranous bone refers to one type of bone formation, bone formed from a primitive connective tissue model (not collagen). Woven bone is early intramembranous bone. The other type of bone is formed from ossification of a cartilaginous model.

Answer 117

The correct answer is D. Within the axilla, the axillary artery is within the axillary sheath and is surrounded by the three cords of the brachial plexus, which are also within the axillary sheath. An aneurysm of the axillary artery may compress any of the three cords. The brachial plexus innervates the shoulder girdle and upper limb with contributions from the ventral rami of spinal nerves C5-T1. The nerves that form this plexus originate from trunks and cords named according to their anatomical location. The axillary nerve (choice A) is a branch of the posterior cord that leaves the axillary sheath, then exits the axilla through the quadrangular space to innervate the deltoid muscle. The long thoracic nerve (choice B) is not within the axillary sheath. It arises from the anterior rami of the fifth, sixth, and seventh cervical nerves in the neck and courses along the chest wall to innervate the serratus anterior muscle. The lower trunk of the brachial plexus (choice C) is not in the axilla. It is formed in the neck from the anterior rami of the eighth cervical and first thoracic spinal nerves. The musculocutaneous nerve (choice E) is not within the axillary sheath. It arises as a branch of the lateral cord of the brachial plexus and enters the arm to innervate the muscles of the anterior compartment of the arm.

Answer 118

The correct answer is E. The trabeculae carneae are ridges of myocardium in the ventricular wall. Remember that the Latin root "carne-" means "flesh" and that the ventricles are "fleshier" than the atria. The auricle (choice A) is derived from the fetal atrium; it has rough myocardium known as musculi pectinati, or pectinate muscle. The crista terminalis (choice B) is the vertical ridge that separates the smooth portion of the right atrium from the rough portion; it extends longitudinally from the superior vena cava to the inferior vena cava. The fossa ovalis (choice C) is the remnant of the fetal foramen ovale, an opening in the interatrial septum that allows blood entering the right atrium from the inferior vena cava to pass directly to the left side of the heart. The sinus venarum (choice D) is the smooth-walled portion of the atrium that receives blood from the superior and inferior vena-cava. It is derived from the fetal sinus venosus.

Answer 119

The correct answer is C. The middle third of the esophagus contains both striated and smooth muscle. The lower third (choice B) of the esophagus, including the lower esophageal sphincter (choice A) contains only smooth muscle. Some authors identify the cricopharyngeus muscle as an upper esophageal sphincter (choice D), despite the fact that unlike a true sphincter, this muscle does not completely encircle the esophagus. The cricopharyngeus is composed exclusively of skeletal muscle; therefore, the biopsy could not have been from this area of the esophagus. The muscularis of the upper third of the esophagus (choice E) is composed entirely of striated muscle.

Answer 120

The correct answer is D. The clavicle is the most frequently broken long bone of the body. However, despite what one might expect, the underlying subclavian vessels and parts of the brachial plexus are only rarely injured. This is because the subclavius muscle, which occupies a small groove on the undersurface of the clavicle, apparently protects the underlying structures. Other functions of this small muscle are not well understood. The deltoid (choice A) originates from the lateral aspect of the clavicle and is a powerful abductor of the arm. The pectoralis major (choice B) originates from the medial aspect of the clavicle and is not as important as the subclavius with regard to protecting underlying structures. The sternocleidomastoid (choice C), an important muscle of the anterior neck, attaches to the medial aspect of the posterosuperior border of the clavicle. The trapezius (choice E), an important muscle of the posterior neck, attaches to the lateral aspect of the posterosuperior border of the clavicle.

Answer 121

The correct answer is A. Grabbing at something to stop oneself, as in the above example, or when a skidding motorcyclist tries to catch a lamp pole, or delivering the arms in an extended position during a breech delivery, are the more common mechanisms by which the lower part of the brachial plexus is damaged. The result of this type of injury is the loss of motor function of the intrinsic hand muscles and numbness along the inner aspect of the hand (ulnar side). The brachial plexus innervates the shoulder girdle and upper limb and divides into the median, radial, and ulner nerves and their branches. There are contributions from the ventral rami and spinal nerves C5-7 into these structures. Damage to the median nerve (choice B) can happen in carpal tunnel syndrome or when a person attempts to cut their wrists. Damage to the radial nerve (choice C) can occur with humeral fractures or when one (often under the influence of alcohol) falls asleep with his or her arm over the back of a chair. Damage to the ulnar nerve (choice D) can occur when the elbow is struck ("funny bone"). Damage to the upper part of the brachial plexus (choice E) can occur when someone falls on the point of the shoulder.

Answer 122

The correct answer is A. The vagus nerve, through its auricular branch, supplies the posterior half of the external auditory meatus. Because the vagus also supplies many other organs, reflex symptoms may occur, including fainting (typically in the elderly), coughing, and gagging. The vagus nerve is sensory from the pharynx, pinna and external auditory canal, diaphragm, and visceral organs in the thoracic and abdominopelvic cavities. It is a motor nerve to the palatal and pharyngeal muscles and visceral organs in thoracic and abdominal cavities. The auriculotemporal nerve (choice B) supplies the anterior half of the external auditory meatus and the facial surface of the upper part of the auricle. The greater auricular nerve (choice C) supplies both surfaces of the lower part of the auricle. The lesser occipital nerve (choice D) supplies the cranial surface of the upper part of the auricle. The vestibulocochlear nerve (choice E) supplies hearing and motion sense.

Answer 123

The correct answer is C. The placenta is derived from both maternal and fetal tissues. The mother produces the capillary bed that forms the lacunar network of the placenta. The fetus produces both the cytotrophoblast (choice B) and the syncytiotrophoblast (choice E), which together form the chorion (choice A). The earliest projections of this are called the primary villi (choice D).

Answer 124

The correct answer is A. The gag reflex requires the glossopharyngeal nerve for the sensory limb of the reflex (unilateral) and the vagus nerve for the motor limb of the reflex (bilateral). A lesion of the left glossopharyngeal nerve will denervate the sensory receptors on the left side of the pharynx, so when the left side is touched, the patient does not feel it and does not gag. If the left vagus nerve is lesioned, the left side of the soft palate will not elevate during a gag, and the uvula will deviate to the right. In this case, the patient only feels the touch on the right side (left glossopharyngeal lesion) and only elevates the right side of the palate (left vagus lesion). If the patient had a lesion of the left glossopharyngeal nerve only (choice B), there would have been no gag reflex when the left side was touched, but there would be a normal gag, without deviation of the uvula, when the right side was touched. If the patient had a lesion of the left vagus nerve only (choice C), the patient would have deviation of the uvula to the right when a gag was elicited, but touching either side of the pharynx would elicit a gag. If the patient had a lesion of the right glossopharyngeal nerve and the right vagus nerve (choice D), touching the right side of the pharynx would not elicit a gag, and touching the left side of the pharynx would elicit a gag with the uvula deviating to the left. If the patient had a lesion of the right glossopharyngeal nerve only (choice E), there would be no gag when the right side was touched, but there would be a normal gag, without deviation of the uvula, when the left side was touched.

Answer 125

The correct answer is C. The lingual nerve is a branch of the mandibular division of the trigeminal nerve that conveys general sensation from the anterior two thirds of the tongue. It enters the oral cavity by passing just under the mandibular third molar between the medial pterygoid muscle and the mandibular ramus. The auriculotemporal nerve (choice A) is a branch of V3 that passes from the infratemporal fossa to the parotid region. It contains sensory fibers from the region in front of the ear and the temporomandibular joint and also conveys postganglionic parasympathetic fibers to the parotid salivary gland. The chorda tympani (choice B) is a branch of CN VII that travels with the lingual nerve in the floor of the mouth. It carries taste fibers from the anterior two thirds of the tongue and preganglionic parasympathetic fibers that synapse in the submandibular ganglion. The mental nerve (choice D) is a sensory branch of the inferior alveolar nerve that supplies the skin of the chin and lower lip. The mylohyoid nerve (choice E) is a motor branch of the inferior alveolar nerve that supplies the mylohyoid and anterior belly of the digastric muscles.

Answer 126

The correct answer is E. The fibers are elastic fibers. You should remember three specific sites where these are found: large arteries (particularly the aorta), vocal cords (or cords), and ligamenta flava (which connect the vertebrae). Small amounts of elastic tissue are also found in skin and to a much lesser degree in other tissues. The vocal folds (or cords) protect the entrance to the glottis. They are located inferior to the ventricular folds. The vocal folds are highly elastic because they contain bands of elastic tissue called the vocal ligaments. The vocal folds are involved in the production of sounds. Elastic tissue is not found in muscle (choice A) or mesentery (choice C). Elastic tissue is not found in substantial amounts in the liver (choice B) or spleen (choice D).

Answer 127

The correct answer is C. The pretracheal layer of the cervical fascia runs from the investing layers in both sides of the lateral neck and splits to enclose the thyroid gland. Superiorly, it attaches to the laryngeal cartilages; inferiorly, it fuses with the pericardium. As a result of these connections, the thyroid gland moves with laryngeal movements. Anatomically, the thyroid gland curves across the anterior surface of the trachea just below the thyroid cartilage that forms most of the anterior surface of the larynx. The two lobes of the thyroid gland are united by a slender connection, the isthmus. The carotid sheath (choice A) contains the vagus nerve, internal jugular vein, carotid artery, and lymph nodes. The investing layer of the deep cervical fascia (choice B) splits to enclose the trapezius and sternocleidomastoid muscles. The prevertebral fascia (choice D) covers muscles arising from the vertebrae. The superficial fascia (choice E) lies immediately deep to the platysma muscle.

Answer 128

The correct answer is C. The middle meningeal artery is a branch of the maxillary artery. It enters the intracranial cavity through the foramen spinosum, which is located in the floor of the middle cranial fossa. A tear of the middle meningeal artery results in accumulation of blood between the inner table of the skull and the dura mater. This is called an epidural hematoma. The anterior cranial fossa (choice A) receives the central processes of the bipolar neurons that form the olfactory nerve. This enters the intracranial cavity via the cribriform plate of the ethmoid bone. The inferior orbital fissure (choice B) contains veins that communicate with venous plexuses in the pterygopalatine and infratemporal fossae. The posterior cranial fossa (choice D) contains the brainstem and cerebellum. The vertebral arteries enter the posterior cranial fossa through the foramen magnum, where they unite to form the basilar artery. The superior orbital fissure (choice E) contains the ophthalmic vein and all of the cranial nerves that innervate the eye (CN III, IV, VI), except for the optic nerve (CN II).

Answer 129

The correct answer is E. The disease described is measles (rubeola), which has the typical presentation described in the question stem. Measles is caused by a Morbillivirus, an RNA virus belonging to the Paramyxovirus family. Koplik spots, which are pathognomonic for measles, are small, bluish-white spots on the buccal mucosa in the early stages of measles. These lesions appear just before the onset of the characteristic rash (which can also involve extremities) and fade as the rash develops. Leukoplakia is a premalignant condition characterized by adherent whitish patches on the gingiva (choice A) and other sites in the oral cavity. Cold sores on the lips (choice B) are caused by infection with Herpes virus. Candida infection (thrush) produces curdy white material loosely attached to an erythematous base (choice C). Aphthous ulcers are large shallow ulcers of the oral mucosa (choice D), commonly known as canker sores.

Answer 130

The correct answer is C. The circle of Willis is a series of arterial anastomoses that circle around the pituitary stalk at the ventral surface of the brain. Specifically, the circle of Willis encircles the infundibulum of the pituitary gland. Hence, the brain can receive blood from either the carotids or the vertebrals. If any of the vessels of the circle of Willis become blocked, blood can be routed through the remaining vessels. The object of this question is to determine which vessel does not belong to the circle of Willis. Of the options listed, only the middle cerebral artery does not belong to the circle and instead courses laterally to supply the entire lateral convexity of the brain. Therefore, ligation of this vessel would produce the most ischemic damage.

Answer 131

The correct answer is D. Endothelium lines the cardiovascular and lymphatic vessels and is composed of simple squamous epithelium. The mesothelium that lines the pleural, pericardial, and peritoneal cavities is also composed of a single-layer of simple squamous epithelium. Pseudostratified epithelium (choice A) is found in the epithelial lining of the respiratory tract, as well as in the transitional epithelium of the urinary system. In simple columnar epithelium (choice B), the cells are taller than they are wide. This epithelium can be found in the intestinal absorptive surface. Simple cuboidal epithelium (choice C) can be found in the ducts of many glands. Stratified columnar epithelium (choice E) can be found in portions of the male urethra.

Answer 132

The correct answer is B. The parotid gland lies lateral to the buccinator muscle. The facial nerve and its branches pass through it. It produces a serous-only salivary secretion, which is second in volume to that produced by the submandibular. The parotid is the largest salivary gland in size. Its duct, known as Stensen's duct, pierces the buccinator in the vicinity of the maxillary second molar.

Answer 133

The correct answer is B. Both the omental bursa and the greater omentum are derived from the dorsal mesogastrium, which is the mesentery of the stomach region. The dorsal mesentery of the stomach becomes greatly enlarged and forms a large pouch that extends inferiorly between the body wall and the anterior surface of the small intestine. This is the greater omentum. The dorsal mesoduodenum (choice A) is the mesentery of the developing duodenum, which later disappears so that the duodenum and pancreas come to lie retroperitoneally. The pericardioperitoneal canal (choice C) embryologically connects the thoracic and peritoneal canals. The pleuropericardial membranes (choice D) become the pericardium and contribute to the diaphragm. The ventral mesentery (choice E) forms the falciform ligament, ligamentum teres, and lesser omentum.

Answer 134

The correct answer is A. The sympathetic trunk lies posterior to the internal jugular vein. Preganglionic sympathetic nerve fibers can be damaged in a cervical trunk injury. These nerve fibers synapse in the superior cervical ganglion on postganglionic sympathetic neurons that innervate structures in the head. The dilator pupillae muscle (smooth muscle of the iris that dilates the pupil) is sympathetically innervated; paralysis of this muscle due to interruption of its innervation results in constriction of the pupil (miosis). Dilation of the pupil (choice B) would result from paralysis of the sphincter pupillae muscle (smooth muscle of the iris that constricts the pupil). This muscle is parasympathetically innervated and would not be affected by this injury. 80 An inability to abduct the eye (choice C) would result from paralysis of the lateral rectus muscle, an extraocular muscle that is innervated by the abducens nerve. It would not be affected by this injury. An inability to close the eye (choice D) would result from paralysis of the orbicularis oculi muscle, a skeletal muscle of the face. This muscle is innervated by the facial nerve and would not be affected by this injury. The platysma muscle (choice E) is a skeletal muscle in the superficial fascia of the neck. It is innervated by the facial nerve and would not be affected by this injury.

Answer 135

The correct answer is choice CIn brief, Cranial Nerve V, the trigeminal, innervates the muscles of mastication, the two tensors, the anterior digastric and the mylohyoid. The muscles of mastication are the medial and lateral pterygoid, the temporalis, and the masseter. The two tensors are the tensor tympani and the tensor (veli) palatini. Note that among the incorrect answers, buccinator, as a muscle of facial expression, is innervated by CN VII, the facial nerve, geniohyoid is innervated by CN XII, the hypoglossal, the posterior digastric is innervated by CN VII, the facial, and levator palatini is innervated by the cervical plexus.

Answer 136

The correct answer is D. The muscles in question are the gluteus medius and gluteus minimus, which are the innervated by the superior gluteal nerve. Textbooks often describe these muscles as abductors of the hip, but in real life, they usually function as described in the question. The femoral nerve (choice A) innervates muscles of the anterior thigh, allowing extension of the leg at the knee. The first and second sacral nerves (choice B) innervate the piriformis muscle, which is a lateral rotator of the thigh at the hip. The obturator nerve (choice C) innervates muscles of the medial thigh. The tibial nerve (choice E) innervates muscles of the posterior lower leg.

Answer 137

The correct answer is D. The splenorenal ligament is the portion of the dorsal mesentery between the posterior abdominal wall and the spleen. This mesentery transmits the splenic artery and vein from their retroperitoneal position in the proximal portion of their course to the peritoneal spleen. The gastrocolic ligament (choice A) is the portion of the greater omentum between the greater curvature of the stomach and the transverse colon. This portion of mesentery is not related to the spleen. The gastrosplenic ligament (choice B) is the portion of the dorsal mesogastrium between the greater curvature of the stomach and the spleen. There are no splenic vessels in this mesentery. The lesser omentum (choice C) is derived from the ventral mesentery. It is the mesentery between the lesser curvature of the stomach and the liver and between the first portion of the duodenum and the liver. It is not related to the spleen.

Answer 138

The correct answer is E. Blue hematoxylin binds to polyanions such as RNA and DNA. Nuclei contain large amounts of DNA and RNA, and they are consequently almost always blue. The nuclei of dysplastic and cancerous cells are often enlarged and hyperchromatic (e.g., darker blue) compared with normal cells of similar cell lines because these altered cells often have extra DNA (are aneuploid) and/or RNA (are metabolically active). Pink eosin binds relatively nonselectively to cellular components, particularly proteins. Cytoplasm of different cell lines can be pink, purple, or blue, depending principally on the number of ribosomes in the cytoplasm. Consequently, blue-tinged cytoplasm tends to suggest high synthetic activity (i.e., abundant ribosomes).

Answer 139

The correct answer is B. The epithelial lining of the second pharyngeal pouch buds into the mesenchyme to form the palatine tonsil. Part of the pouch remains in the adult as the tonsillar fossa. It is important to review the other choices because pharyngeal pouch derivatives are typically tested on the NBDE part 1. The first pharyngeal pouch (choice A) develops into the middle ear cavity and eustachian tube. The third pharyngeal pouch (choice C) develops into the thymus and the inferior parathyroid glands. The fourth pharyngeal pouch (choice D) gives rise to the superior parathyroid glands. Recall that abnormal development of the third and fourth pouches leads to DiGeorge syndrome and results in hypocalcemia, as well as abnormal cellular immunity and consequent susceptibility to viral and fungal illnesses. The fifth pharyngeal pouch (choice E) gives rise to the C cells of the thyroid gland. These cells secrete calcitonin, a hormone that lowers serum calcium.

Answer 140

The correct answer is A. The muscle that moves the hyoid anteriorly to open the pharynx is the geniohyoid. This muscle is innervated by the ansa cervicalis branch of C1. The ansa cervicalis also innervates the thyrohyoid and the intra hyoids. Cranial nerve IX (choice B) innervates the stylopharyngeus. The pharyngeal plexus (choice C) innervates the palatoglossus, palatopharyngeus, and cricopharyngeus. Cranial nerve V-3 (choice D) innervates most of the muscles of mastication. Cranial nerve VII (choice E) innervates the buccinator and other muscles of facial expression.

Answer 141

The correct answer is E. A posterolateral herniation of the nucleus pulposus is the most common type of herniation. This herniation results in the nucleus pulposus occupying space within the intervertebral foramen. The spinal nerve in the intervertebral foramen between vertebrae C4 and C5 is the C5 spinal nerve. The anterior and posterior rami (choices A and B) are found lateral to the intervertebral foramina and are not compressed by a herniated nucleus pulposus. The spinal cord (choice C) is within the vertebral canal. A posterior herniation of a nucleus pulposus (less common) may compress the spinal cord. Spinal nerve C4 (choice D) is found in the intervertebral foramen between vertebrae C3 and C4 and would not be compressed by this herniation.

Answer 142

The correct answer is A. The axillary nerve can be damaged during anterior dislocation of the shoulder, causing loss of sensation in the skin overlying the lower half of the deltoid muscle. The median nerve (choice B) supplies sensation to the anterior arm, palm, and distal aspects of the lateral three-and-a-half fingers. The musculocutaneous nerve (choice C) supplies sensation to the lateral surface of the arm and forearm. The radial nerve (choice D) supplies sensation to the back of the arm, forearm, and hand. The ulnar nerve (choice E) supplies sensation to the medial side of the arm, forearm, and hand.

Answer 143

The correct answer is C. Approximately half of all spontaneous abortions are of fetuses with major chromosomal defects, most commonly trisomy 16, triploidy (due to fertilization of an egg by two sperm), and 45 X,0 (Turner's syndrome). Trisomy 16 and triploidy do not produce viable offspring, unlike 45 X,0. Trisomy 8 (choice A) is one of the very rare causes of live birth trisomies. Trisomy 13 (choice B) is one of the more common live birth trisomy syndromes (Patau syndrome). Trisomy 18 (choice D) is one of the more common live birth trisomy syndromes (Edwards' syndrome) Trisomy 21 (choice E) causes Down's syndrome.

Answer 144

The correct answer is E. The sequence of the auditory pathway is as follows: Organ of Corti → spiral ganglion in the cochlea vestibulocochlear nerve (CN VIII) → cochlear nuclei (dorsal and ventral) → superior olivary nuclei → lateral lemniscus → inferior colliculus → medial geniculate → nucleus of the thalamus (MGN) → primary auditory cortex (Heschls gyrus). Each ear projects to both sides of the brainstem and cortex by way of multiple commissures, including the trapezoid body (which contains fibers crossing contralateral to the superior olivary nucleus), the commissure of the inferior colliculus (connecting the right and left inferior colliculi), and another commissure that connects the right and the left nuclei of the lateral lemniscus. A lesion of any structure up until the superior olivary nuclei therefore will produce an ipsilateral deafness. The only structure listed that is proximal to the superior olivary nuclei is the organ of Corti (choice E). The inferior colliculus (choice A), the lateral lemniscus (choice B) and the medial geniculate body (choice C) all receive information from both ears, and unilateral hearing loss could not result from a lesion of any of these structures. The medial lemniscus (choice D) is not a part of the auditory system. It is part of the somatosensory system, which conveys proprioception, discriminative touch, and vibration information. More specifically, neurons of the gracile and cuneate nuclei send projections that decussate as the internal arcuate fibers and ascend as the medial lemniscus to synapse in the ventroposterolateral nucleus (VPL) of the thalamus.

Answer 145

The correct answer is D. Pasteurella multocida is a gram-negative rod that is normal flora of the oral cavity of dogs and cats. It often causes a local abscess following introduction under the skin by an animal bite. Most cases occur in children who are injured while playing with a pet. Bartonella henselae (choice A) is a very small, gram-negative bacterium that is closely related to the rickettsia, although it is able to grow on lifeless media. It is the cause of catscratch disease (a local, chronic lymphadenitis most commonly seen in children) and bacillary angiomatosis (seen particularly in patients with AIDS). In this latter patient population, the organism causes proliferation of blood and lymphatic vessels, causing a characteristic "mulberry" lesion in the skin and subcutaneous tissues of the afflicted individual. Brucella canis(choice B) is a gram-negative rod that is a zoonotic agent. Its normal host is the dog, but when it gains access to humans, it causes an undulating febrile disease with malaise, lymphadenopathy, and hepatosplenomegaly. The normal route of exposure is by way of ingestion of the organism. Clostridium tetani(choice C) is a gram-positive spore-forming anaerobic rod. It causes tetanus (a spastic paralysis caused by tetanospasmin). There may be no lesion at the site of inoculation, and exudation would be extremely rare.

Answer 146

The correct answer is B. In compact bone, the bone is in concentric layers, and small spaces between layers house the osteocytes, or mature bone cells. These small spaces are called lacunae. Radiating out from the lacunae are small conducting vessels known as canaliculi. They help bring nutrients to and waste from the osteocytes. Remember that bone matrix does not allow diffusion readily. The original source of nutrients to compact bone is Haversian canals, which contain arteries, veins, and nerves. Smaller perpendicular branches of these canals are sometimes called Volkman canals. Osteons are also called Haversian systems, and consist of the Haversian canal, the concentric bone layers around them, the osteocytes in the concentric rings, the lacunae and canaliculi. Osteons are found in compact (lamelllar) bone.

Answer 147

The correct answer is B. The vertical dimension of occlusion (VDO) is a vertical measurement on the front of the face when the teeth are in full occlusion (centric occlusion). When the face is at rest, the teeth are slightly apart, and the vertical dimension of the front of the face is slightly longer. This is the vertical dimension of rest (VDR). The distance between the teeth at this point is the freeway space (FS). So when we take the smaller VDO and add the few millimeters of the FS, we get the slightly longer VDR. VDR is generally 2 to 5 mm more than VDO.

Answer 148

The correct answer is E. Bone matrix is generally impermeable to diffusion of nutrients for any great distance. Osteocytes in need of food and oxygen, and also needing to excrete waste, therefore need to be near some transport system. In compact bone, Haversian canals carry arteries, veins, capillaries, and nerves. Horizontal branches of these canals are sometimes termed Volkman canals. Small canaliculi (small canals) branch out of these canals, and also radiate from the lacunae that house the osteocytes. All of these structures therefore can be involved in nutrient transport. Cartilaginous matrix, unlike osseous (bone) matrix, is permeable, slowly, to nutrient travel. There is no cartilaginous matrix, however, in fully formed bone tissue.

Answer 149

The correct answer is A. Parathormone (PTH) is secreted by principal cells of the parathyroid glands, small gland pairs embedded in thyroid tissue. Parathyroid hormone will increase the level of serum calcium by increasing bone calcium resorption, increasing digestive absorption of calcium, and decreasing kidney excretion of calcium. The bone resorbing cells are osteoclasts, which are large, multinucleated cells. Osteoblasts are boneformers and secrete bone matrix, primarily of collagen. Osteocytes are mature bone cells living in lacunae in compact bone. Osteosarcomas are malignant tumors of bone.

Answer 150

The correct answer is C. Permanent (non-dividing) cells have left the cell cycle and can no longer undergo mitotic division. Examples that are usually cited include neurons and cardiac myocytes. One of the major disadvantages of these cells is that once they are damaged or destroyed, they do not regenerate. Examples of labile (continuously dividing) cells (choices A and B) include the epithelia of the body surface, gastrointestinal tract, and urinary tract. Examples of stable (quiescent) cells (choices D and E) include the cells of the liver and the glandular organs of the body.

Answer 151

The correct answer is B. The renal artery (choice D) enters the kidney at the hilum and immediately divides into the interlobar arteries (choice C). These arteries supply the renal pelvis and capsule before passing between the medullary pyramids to the corticomedullary 87 junction. They then bend almost 90 degrees to form the short, arching arcuate arteries (choice B), which run along the corticomedullary junction. The arcuate arteries subdivide into the fine interlobular arteries. These interlobular arteries give off branches that become the afferent arterioles (choice A) of the glomerulus.

Answer 152

The correct answer is B. The recurrent laryngeal nerves are branches of the vagus (CN X) and supply all intrinsic muscles of the larynx, except the cricothyroid. The right recurrent laryngeal nerve recurs around the right subclavian artery. The left recurrent laryngeal nerve recurs in the thorax around the arch of the aorta and ligamentum arteriosum. Both nerves ascend to the larynx by passing between the trachea and esophagus, close to the thyroid gland. The internal laryngeal (choice A) nerve is a purely sensory branch of the superior laryngeal nerve. The thyroarytenoid (choice C) is an intrinsic muscle of the larynx; its inner fibers are specialized as the vocalis muscle, which is related to the vocal ligament. It is not usually at risk during thyroid surgery. The vestibular folds (choice D), or false vocal folds, are located superior to the true vocal folds inside the larynx. They are not concerned with phonation. The vocal folds (choice E) form the boundaries of the rima glottidis inside the larynx and are not vulnerable during thyroidectomy.

Answer 153

The correct answer is A. The obturator nerve innervates the muscles of the medial compartment of the thigh. The adductors are located inferior to the acetabular surface. These include the adductor longus, adductor brevis, adductor magnus, and gracilis muscles. The adductor magnus is also innervated by the tibial nerve. The biceps femoris (choice B) is in the posterior compartment of the thigh. The long head of the biceps femoris is innervated by the tibial portion of the sciatic nerve, and the short head of the biceps femoris is innervated by the common peroneal portion of the sciatic nerve. 88 The rectus femoris (choice C) and vastus medialis (choice E) are two of the four heads of the quadriceps femoris muscle. All four heads of the quadriceps femoris muscle are in the anterior compartment of the thigh and are innervated by the femoral nerve. The sartorius muscle (choice D) is in the anterior compartment of the thigh and is innervated by the femoral nerve.

Answer 154

The correct answer is E. The palpable space immediately inferior to the clavicle is the first intercostal space, and the bone below it is the second rib. The acromion (choice A) is the lateral extension of the scapular spine. The atlas (choice B) is the first cervical vertebra, articulating with the occipital bone above and the axis below. The first rib (choice C) is hidden under the clavicle. The manubrium (choice D) is the most superior portion of the sternum.

Answer 155

The correct answer is A.. The right lymphatic duct drains the right arm, the right side of the chest, and the right side of the head. The thoracic duct drains the rest of the body. Both the right lymphatic duct and the thoracic duct dump into the large venous channels at the base of the neck at the junction of the subclavian vein and internal jugular vein. Occlusion of this drainage can produce intractable edema in sites feeding these ducts. The left side and right leg would be affected, rather than the right side and left leg (choice B). The entire left side (rather than just the left arm, choice C) and right leg drain into the thoracic duct. The right arm and the right half of the head (choices D and E) drain to the right lymphatic duct.

Answer 156

The correct answer is D. The metanephric duct (also known as the ureteric bud) is a diverticulum of the mesonephric duct. It grows to the metanephric mass of the urogenital ridge. It induces the development of the metanephros, which will give rise to the excretory units of the definitive kidney. The metanephros, in turn, induces the metanephric duct to divide into the calyces and the collecting tubules. The allantois (choice A) is an endodermal diverticulum of the yolk sac. It becomes incorporated into the urogenital sinus and contributes to the formation of the urinary bladder. It is not involved with the formation of the kidney. The mesonephric duct (choice B) is a mesodermal duct into which the mesonephric tubules drain. The mesonephric duct is the same as the pronephric duct, but at a later stage of development. The mesonephric duct develops into the ductus deferens in the male. The metanephric duct is a diverticulum of the mesonephric duct. The mesonephros (choice C) is the embryonic kidney, which functions in the embryo before the metanephros (or definitive kidney) develops. The mesonephros develops from the urogenital ridge. The urogenital ridge (choice E) is a longitudinal elevation of the intermediate mesoderm. The embryonic and adult kidneys, as well as the gonads, develop from this mesoderm.

Answer 157

The correct answer is B. The carpal bone that has been dislocated is the lunate, one of the four proximal carpal bones. This bone has been dislocated into the carpal tunnel, which is anterior to the carpal bones. The median nerve is the only nerve that traverses the carpal tunnel. The anterior interosseous nerve (choice A) is a branch of the median nerve that arises in the proximal forearm and innervates the deep muscles of the anterior forearm. This nerve does not traverse the carpal tunnel. The posterior interosseous nerve (choice C) is a branch of the radial nerve that arises in the proximal forearm and innervates several muscles of the posterior compartment of the forearm. This nerve does not traverse the carpal tunnel. The radial nerve (choice D) innervates posterior muscles of the arm, some posterior muscles of the forearm, and areas of skin on the posterior surface of the upper limb. It does not pass through the carpal tunnel. The ulnar nerve (choice E) innervates some muscles in the anterior compartment of the forearm and many muscles in the hand. The nerve crosses the wrist superficial to the flexor retinaculum and is therefore not within the carpal tunnel. It is spared compression by the dislocation of the lunate.

Answer 158

The correct answer is B. This question is essentially asking, "Which of the following nerves innervates the anatomical structures listed?" This patient has acromegaly, which is characterized by overgrowth of the face, jaws, hands, and feet, enlargement of internal organs, hyperglycemia, hypertension, and osteoporosis. It is caused by hypersecretion of growth hormone, often attributed to an adenohypophyseal tumor. Complications include degenerative joint disease, muscular weakness, neuropathies, and diabetes mellitus. In this question, although the patient's sensory symptoms may be caused by a neuropathy, it is very likely that overgrowth in the wrist area has compressed the carpal tunnel, thereby impinging on the median nerve. Note that the median nerve (root C5-T1) provides motor innervation to the forearm flexors, thenar muscles, and radial lumbricals. It provides sensory innervation to the radial 2/3 of the palm, volar surfaces of the thumb, second and third digits, and radial 1/2 of the fourth digit, as well as the skin over the lateral surface of the hand. Damage to the anterior interosseus nerve (choice A), also known as the deep branch of the median nerve, results in the inability to form a round "O" with the thumb and forefinger. This is due to impaired function of the flexor pollicis longus. Damage to the anterior interosseus nerve could explain the patient's thumb dysfunction, but it would not account for the patient's paresthesias in the first three digits of the hand. The musculocutaneous nerve (choice C) innervates the arm flexors and provides sensory information to the anterolateral forearm. It is composed of contributions from C5-C7. The radial nerve (choice D) innervates the extensors of the arm and forearm and skin of the posterior arm, forearm, and radial half of the dorsum of the hand (not including the fingertips). It is composed of contributions from C6-C8. The ulnar nerve (choice E) provides motor innervation to the ulnar flexors, adductor pollicis, hypothenar muscles, interosseus muscles, and lumbricals 4 and 5. It provides sensory innervation to the ulnar half of the wrist, palm, and fourth and fifth digits. It is composed of contributions from C8-T1.

Answer 159

The correct answer is C. The greater (long) saphenous vein starts on the dorsal surface of the foot, wraps proximally to follow the medial aspect of the leg below and past the knee, and then dives into the deep fascia through the fossa ovalis (also called the saphenous opening) to reach the femoral vein, which becomes the external iliac vein shortly after it is joined by the greater saphenous vein. The anatomic snuff box (choice A) is on the wrist. Some authors also refer to an "anatomic snuff box of the foot," through which the saphenous vein does pass, but this is early in its course, and not just before it joins the femoral vein. The antecubital fossa (choice B) is at the elbow. The inguinal canal (choice D) contains structures going to and from the testes. The saphenous vein passes near, but not through, the popliteal fossa (choice E) to cross the knee.

Answer 160

The correct answer is B. Fenestrated ("windowed") endothelial cells, which permit free flow of serum across the endothelium, are an unusual feature of the hepatic sinusoids. They are not seen in the other organs listed. Along the same line, fenestrated capillaries are capillaries containing "windows" or pores that span the endothelial lining. The pores permit the rapid exchange of water and solutes as large as small peptides between the plasma and interstitial fluid.

Answer 161

The correct answer is B. The major depressor (opener) is the lateral pterygoid, which also protrudes and causes lateral motion. Mylohyoid, digastric, and geniohyoid can aid this motion. Mylohyoid can produce opening movement by contracting between the hyoid bone and the mylohyoid line on both sides of the mandible. The anterior digastric produces an opening motion as it contracts between the digastric facial sling on the hyoid bone and the interior of the mandible (digastric fossa). The geniohyoid can contract between the hyoid bone and the genial tubercle on the mandibular symphysis.

Answer 162

The correct answer is A. This may seem like an obscure fact, but it is a perennial NBDE favorite. The tensor veli palatini wraps around a small hook-like extension of the medial pterygoid plate of the sphenoid bone, known as the pterygoid hamulus. The tensor (veli) palatini originates from the greater wing of the sphenoid and from cartilage of the auditory tube. The fibers converge into a tendon, which sharply hooks around the pterygoid hamulus. The fibers then join with their partners from the other side to form the palatal aponeurosis to which most of the muscles of the soft palate are attached. The muscle tenses the soft palate, especially during swallowing.

Answer 163

The correct answer is B. The ear has a complex sensory nerve supply, which includes all of the nerves listed. A consequence of this complexity is that pain actually originating in other sites (teeth and sinuses are notorious) may be misinterpreted as ear pain; or, less commonly, pain originating in the ear may be misinterpreted as arising from other sites. The anterior half of the external ear canal is supplied by the auriculotemporal nerve, which also supplies the facial surface of the upper part of the auricle. The auricular branch of the vagus (choice A) supplies the posterior half of the external ear canal. The greater auricular nerve (choice C) supplies both surfaces of the lower part of the auricle. The lesser occipital nerve (choice D) supplies the cranial surface of the upper part of the auricle. The vestibulocochlear nerve (choice E) supplies hearing and motion sense.

Answer 164

The correct answer is C. The bilaminar disc forms in the second week of embryonic life by differentiation of embryoblast cells into epiblast (primary ectoderm adjacent to the amniotic cavity) and hypoblast (primary endoderm adjacent to the yolk sac; (choice E) layers. During the third week of life, a linear thickening of some of the epiblast cells produces a primitive streak, bounded rostrally by the primitive node (choice D). Epiblast cells migrate from the primitive streak downward, replacing the original hypoblast with definitive endoderm (choice B). The migrating epiblast also fills the potential space between the two layers with a third germ layer, the intraembryonic mesoderm (choice C). The remaining epiblast cells (which don't migrate) form the definitve ectoderm (choice A).

Answer 165

The correct answer is A. The cells described are the primordial eggs, which remain stopped in the diplotene stage of the first meiotic division from before birth until fertilization, a period which may be 40 or more years. Choices B and E are incorrect because the oocytes are stopped in the first, not the second, meiotic division. Choices C and D are incorrect because the cells described are oocytes and are not in mitosis.

Answer 166

The correct answer is A. The internal epithelial lining of the trachea, bronchi, and lungs form from a diverticulum of the ventral foregut wall (endoderm) called the respiratory diverticulum. The midgut endoderm (choice B) gives rise to the internal epithelial lining of much of the gastrointestinal tract, duodenum, small intestine, ascending colon, and right two thirds of transverse colon. The splanchnic mesoderm (choices C and E) contributes only to the smooth muscle coat and cartilaginous skeleton of the trachea and bronchi. The stomodeum (choice D) is of ectodermal origin and gives rise to the mouth. The stomodeum eventually becomes continuous with the endodermal foregut of the larynx (and trachea) and the esophagus.

Answer 167

The correct answer is E. The condition described is spina bifida with myelomeningocele. A failure of the posteriorly located vertebral arches to fuse posteriorly causes spina bifida, which can vary in severity from a completely asymptomatic, minor abnormality to protrusion of the spinal cord and roots through an open skin defect, with a very real risk of minor trauma or infection causing paralysis. The bodies of the vertebrae (choice A) are the stacking ovoid structures on the anterior aspect of the spinal canal. The pedicles (choice B) attach the body ring that surrounds the spinal canal to the body of the vertebrae. Failure of development of one of the paired primary ossification centers (choice C) of the body can produce very severe scoliosis. The superior articular process (choice D) articulates with the inferior articular facet of the vertebra above it

Answer 168

The correct answer is E. Bone is formed by type I collagen fibers, ground substance, and hydroxyapatite crystals. The collagen is oriented in a layered or lamellar fashion. It can be parallel (trabecular bone and periosteum) or concentric (Haversian system). When bone is formed quickly, as in a healing fracture site, metabolic bone disease, or tumor, the collagen is randomly oriented and is called woven bone. Compact bone (choice B) is the dense, calcified, external part of the bone. It is lamellar bone. Cancellous (choice A), spongy (choice C), and trabecular (choice D) bone are all synonymous terms for the thinner network of bone within the cortex.

Answer 169

The correct answer is A. The lateral pterygoid muscles consist of two heads, an upper head arising from the infratemporal surface of the greater wing of the sphenoid bone, and a lower head arising from the lateral pterygoid plate. The lateral pterygoids act to pull the mandible forward in the process of opening the jaw. Other actions include protracting the mandible and moving it from side to side (as in chewing). The lateral pterygoid is innervated by the mandibular branch of the trigerminal nerve. The masseter (choice B) and medial pterygoid (choice C) muscles help to close the jaw, while the temporalis (choice E) closes and retrudes the mandible. All of these muscles are innervated by the mandibular branch of the trigeminal nerve. The orbicularis oris (choice D) muscle purses the lips. It is innervated by the facial nerve.

Answer 170

The correct answer is C. C5 helps mediate flexion, abduction, and lateral rotation of the shoulder, and flexion of the elbow. Both C5 and C6 mediate extension of the elbow. Extension of the fingers (choice A) is mediated by C7 and C8. Extension of the shoulder (choice B) is mediated by C7 and C8. Flexion of the wrist (choice D) is mediated by C6 and C7. Pronation of the elbow (choice E) is mediated by C7 and C8.

Answer 171

The correct answer is E. The hypophysis, or pituitary gland, is approached transnasally through the sphenoid sinus. This small gland lies within the sella turcica, a depression in the sphenoid bone. The pituitary gland hangs beneath the hypothalamus, connected by a slender stalk, the infundibulum. The base of the infundibulum lies between the optic chiasm and mamillary bodies. Inadvertent transgression into the cavernous sinus (choice A) would lead to torrential venous or arterial hemorrhage from the cavernous sinus itself or the internal carotid artery contained within. The ethmoid sinus (choice B) is related to the medial wall of the orbit. The frontal lobe lies behind the frontal sinus (choice C). The mastoid sinus (choice D) lies within the temporal bone and communicates with the middle ear.

Answer 172

The correct answer is A. The pharyngeal arches are outpouchings of tissue visible on the external neck of the embryo. They are separated by the pharyngeal clefts (each one caudal to its arch). The pharyngeal pouches are the outpouchings of the pharynx visible inside the embryo that correspond to the arches. The defect described is due to abnormal development of the derivatives of the first pharyngeal arch. It is thought that the initial defect may be insufficient migration of neural crest cells.

Answer 173

The correct answer is A. The interlaminar space is the space between the laminae of the lumbar vertebrae. The ligamentum flavum crosses the interlaminar space. Because there is a gap between the right and left ligamentum flavum in the midline, this ligament is not penetrated if the needle is in the midline. Immediately within the bony vertebra is the epidural space, which lies between the bone and the dura. The epidural space contains a considerable amount of fat and a venous plexus. Because the muscles of the back are located on either side of the midline, no muscle is penetrated when doing a lumbar puncture (choice B). The subarachnoid space (choice C), which is filled with cerebrospinal fluid, is reached after the needle passes through the epidural space and pierces the dura and arachnoid. The cauda equina, rather than the spinal cord, is located in the subarachnoid space of the low lumbar region where a lumbar puncture is performed. The subcutaneous space (choice D) contains superficial fascia and fat and is found immediately beneath the skin. After passing through the subcutaneous fascia, the needle passes through the supraspinous ligament and the interspinous ligament. The subdural space (choice E) is a potential space between the dura and arachnoid. Normally, this space does not exist because the arachnoid is closely applied to the dura. If there were bleeding into this potential space, the two layers would separate and a subdural hematoma would be produced.

Answer 174

The correct answer is E. Saying "la" requires the tongue to be placed against the roof of the mouth, which cannot be accomplished if the hypoglossal nerve (CN XII) is nonfunctional. CN XII innervates the intrinsic muscles of the tongue. The hypoglossal nerve innervates the genioglossus, hypoglossus, palatoglossus, and styloglossus muscles of the tongue. The facial nerve, CN VII (choice A), is needed to move the lips while saying "mi." CN VII innervates the muscles of facial expression. The vestibulocochlear nerve, CN VIII (choice B), mediates hearing and maintains equilibrium and balance. The vagus nerve, CN X (choice C), is needed to raise the palate while saying "kuh." The spinal accessory nerve, CN XI (choice D), mediates head and shoulder movements.

Answer 175

The correct answer is C.The first part of answering the question is to recognize the terminology. In particular, the NBDE often uses the term neurohypophysis for posterior pituitary, and adenohypophysis for anterior pituitary. The only two hormones of the posterior pituitary (neurohypophysis) are ADH (vasopressin), which increases water reabsorption by the kidney, and oxytocin, which stimulates uterine contractions during labor and delivery. All other pituitary hormones are anterior, form the adenohypophysis. They include FSH (follicle stimulating hormone), which acts on the ovary, TSH (Thyroid stimulating hormone), which acts on the thyroid, LH (luteinizing hormone), which acts on the ovary, and STH (GH, growth hormone) which stimulates long bone growth, and especially acts on epiphyseal plates.

Answer 176

The correct answer is C. The arterial supply of the stomach is complex; it therefore has a good potential to appear on the NBDE. The right gastric artery supplies the distal lesser curvature. The left gastric artery (choice A) supplies the proximal lesser curvature. The left gastroepiploic artery (choice B) supplies the proximal greater curvature below the splenic artery. The right gastroepiploic artery (choice D) supplies the distal greater curvature. The short gastric artery (choice E) supplies the proximal greater curvature above the splenic artery.

Answer 177

The correct answer is E. The anterior pituitary produces prolactin. The structure originates from Rathke's pouch, which is itself a diverticulum of the roof of the stomodeum. The cerebral vesicle (choice A) lies close to Rathke's pouch. The infundibulum (choice B) comes in contact with Rathke's pouch at the fifth week of development. The neurohypophysis (choice C) gives rise to the posterior pituitary. The proctodeum (choice D) is also known as the anal pit.

Answer 178

The correct answer is B. The muscle deep to the breast is the pectoralis major. Breast cancer can invade this muscle but usually does not because the relatively thick, deep fascial layer serves as a barrier. Formerly, the pectoralis major was removed during radical mastectomy, leaving the patient with a major loss of function of the adjacent arm. The now more frequently used modified radical mastectomy spares the pectoralis major. The external obliques (choice A) and rectus abdominis (choice D) muscles are in the abdomen. The platysma (choice C) and sternocleidomastoid (choice E) muscles are in the neck.

Answer 179

The correct answer is A. Astrocytes and oligodendrocytes are both derived from glioblasts, which, in turn, are derived from neuroepithelial cells. Other neuroepithelial cell derivatives include neuroblasts and ependymal cells. The astrocytes are the largest and most numerous glial cells. These cells are responsible for maintaining the blood-brain barrier, creating a three-dimensional framework for the central nervous system, performing repairs in damaged neural tissues, and controlling the interstitial environment. All the other choices are derived from neural crest cells. Other neural crest derivatives include the neurons of the parasympathetic and sympathetic ganglia (including the adrenal medulla), the dorsal root ganglia of the peripheral nervous system, the sensory ganglia of cranial nerves V, VII, IX, and X, and the leptomeninges (pia and arachnoid).

Answer 180

The correct answer is A. Although many students memorize the innervation of the tongue, it can also be explained in a developmental way. In particular, the tongue is derived from the first three pharyngeal (branchial) arches, and the cranial nerves associated with each arch appear from anterior to posterior in the tongue innervation. Note that some texts also state that the most posterior sections of the tongue are developed form the fourth arch as well. The cranial nerves of each arch are as follows: Arch 1 (CN V), Arch 2 (CN VII), Arch 3 (CN IX), and Arch 4 (CN X). Note that general sensation from the anterior two thirds of the tongue is supplied by CN V, taste by CN VII, taste and general sensation from the posterior one third are supplied by CN IX, and some innervation of the most posterior tongue by CN X.

Answer 181

The correct answer is C. The neurohypophysis (posterior pituitary) is derived from an evagination of the diencephalic neurectoderm. This structure is responsible for releasing oxytocin and vasopressin to the general circulation. Both hormones are synthesized in cell bodies contained within the hypothalamus. Oxytocin is a hormone produced by the hypothalamic cells and secreted into capillaries at the posterior pituitary. It stimulates smooth muscle contractions of the uterus or mammary glands in the female, but has no known function in the male. ACTH (choice A), prolactin (choice D), and TSH (choice E) are all synthesized and released by the anterior pituitary, or adenohypophysis, which is derived from an evagination of the ectoderm of Rathke's pouch, a diverticulum of the primitive mouth. Remnants of this pouch may give rise to a craniopharyngioma in later life. Epinephrine (choice B) is synthesized and released into the circulation by the adrenal medulla, a neural crest derivative.

Answer 182

The correct answer is B. A meningioma (a tumor of the meninges) of the parasagittal region and the falx cerebri would be located superiorly, between the two hemispheres. In this 101 position, it could compress the sensory (postcentral gyrus) or motor cortex (precentral gyrus) supplying the lower extremities. Taste (choice A) is supplied by cranial nerves VII, IX, and X. These nerves arise in the brainstem. Facial sensation (choice C) is supplied by cranial nerve V, the nuclei of which are in the brainstem. Ptosis (choice D) can be caused by a deficit in cranial nerve III, which arises from the brainstem. Unilateral deafness (choice E) suggests damage to cranial nerve VIII, which arises from the brainstem.

Answer 183

The correct answer is D. Rough endoplasmic reticulum present in neurons is called Nissl substance, or Nissl bodies. Nissl bodies stain intensely with basic dyes and are found in the cell body and proximal dendrites, but not in the axon hillock or axon.

Answer 184

The correct answer is A. Bregma represents the point where the coronal and sagittal sutures intersect; it is the site of the anterior fontanelle. The coronal suture (choice B) lies between the frontal and parietal bones. Lambda (choice C) represents the point where the sagittal and lambdoid sutures intersect; it is the site of the posterior fontanelle in infants. The pterion (choice D) is the point on the lateral aspect of the skull where the greater wing of the sphenoid, parietal, frontal, and temporal bones converge. Recall that the pterion is the landmark for the middle meningeal artery and that a blow to the temple (e.g., as could occur in boxing) can lead to a middle meningeal arterial bleed and an epidural hemorhage. The sagittal suture (choice E) is located between the two parietal bones.

Answer 185

The correct answer is E. The mandibular nerve (V3) passes through the foramen ovale and may be injured by this fracture. The mandibular nerve is responsible for the innervation of all of the muscles of mastication: the masseter, the temporalis, the medial pterygoid, and the lateral pterygoid muscles, as well as the tensor palatini, tensor tympani, and mylohyoid. Abduction of the eye (choice A) is produced by the lateral rectus muscle, which is innervated by the abducens nerve. The abducens nerve leaves the cranial cavity and enters the orbit by passing through the superior orbital fissure. Sensation in the skin over the forehead (choice B) is provided by the ophthalmic division of the trigeminal nerve. The ophthalmic division leaves the cranial cavity and enters the orbit by passing through the superior orbital fissure. Sensation in the skin over the zygoma (choice C) is provided by the maxillary division of the trigeminal nerve. The maxillary division leaves the cranial cavity by passing through the foramen rotundum and enters the pterygopalatine fossa. Taste sensation on the anterior 2/3 of the tongue (choice D) is provided by the chordae tympani, a branch of the facial nerve. The facial nerve leaves the cranial cavity by passing into the internal auditory meatus and enters the temporal bone. The chordae tympani leaves the temporal bone by passing through the petrotympanic fissure and enters the infratemporal fossae.

Answer 186

The correct answer is C. Cleft lip is caused by the failure of the maxillary processes to fuse with the medial nasal swellings. Abnormal development of the third and fourth pharyngeal pouches (choice A) can give rise to DiGeorge syndrome, which is characterized by the underdevelopment or absence of several structures, including the thymus and parathyroids. Bony defects of the malar bone and mandible (choice B) are associated with mandibulofacial dysostosis, which is mainly due to abnormal development of derivatives of the first arch. This condition is characterized by downward sloping palpebral fissures; hypoplasia of the malar and mandibular bones; macrostomia; high or cleft palate; abnormally shaped, low-set ears; and unusual hair growth patterns. Insufficient migration of neural crest cells (choice E) is an important factor as well. When the palatine shelves fail to join together (choice D), cleft palate results. Cleft lip and cleft palate commonly co-occur.

Answer 187

The correct answer is A. The structure described is the ligamentum venosum (choice D), which is derived from the ductus venosus. The hepatic portal vein (choice B) is derived from the vitelline vein (choice E). The lateral splanchnic arteries (choice C) arise from each side of the dorsal aorta. They supply intermediate mesoderm and derivatives and give rise to renal, suprarenal, phrenic, and testicular or ovarian arteries.

Answer 188

The correct answer is B. The left suprarenal vein empties into the left renal vein, which crosses the vertebral column to reach the inferior vena cava. The left renal vein also receives the left gonadal vein. Hepatic veins (choice A) convey blood from the liver to the inferior vena cava as it approaches the caval orifice of the diaphragm. The right gonadal vein (testicular in male, ovarian in female; choice C) drains directly to the inferior vena cava. The left and right (choice D) renal veins enter the inferior vena cava at vertebral level L2.

Answer 189

The correct answer is C. There are two systems currently used for classifying nerve fibers. The first system groups both sensory and motor fibers together, describing A-α±, A-β, A-Γ, A- Δ, B, and C fibers. Another system relates only to sensory fibers, describing Ia, Ib, II, III, and IV categories. Both classification schemes begin with large, myelinated fibers, progressing to finer, unmyelinated fibers. 104 The C fiber (or IV fibers) is the only type of fiber that is unmyelinated. Remember that preganglionic neurons are myelinated, but postganglionic neurons are unmyelinated. Neurons that carry slow pain and temperature information are also classified as C fibers. See the table below for more information. A-α± or Ia (choice D) Alpha motor neurons, primary afferents of muscle spindles A-α± or Ib (choice E) Golgi tendon organ afferents, touch and pressure A-β or II Secondary afferents of muscle spindles, touch and pressure A-Γ Gamma motor neurons A-Δ (choice A) Touch, pressure, pain and temperature (fast) B (choice B) Preganglionic autonomic, visceral afferents C (choice C) IV Postganglionic autonomic, pain and temperature (slow)

Answer 190

The correct answer is E. Physiologically, the distribution of the radial nerve is as follows: extensor muscles on the arm and forearm (triceps bracii, brachioradialis, extensor carpi radials, and extersor carpi ulnaris), ditigal extensors and abductor pollicis, and skin over the posterolateral surface of the arm. The radial nerve lies in the musculospiral groove of the humerus and is subject to injury in association with a fracture of the midshaft of the humerus. The radial nerve innervates the extensor muscles of the forearm, including the muscles that extend the wrist; paralysis of these muscles results in a wrist drop. Although the muscles responsible for flexing the digits are not innervated by the radial nerve, the making of a tight fist requires that the wrist be stabilized with the wrist extensors. The axillary nerve (choice A) leaves the axilla through its posterior wall and is not located in the region of the midshaft of the humerus. The axillary nerve innervates the deltoid and the teres minor muscles, neither of which have any function in the hand. The long thoracic nerve (choice B) lies against the chest wall and is not subject to injury as a result of a humeral fracture. The long thoracic nerve innervates the serratus anterior muscle. The median nerve (choice C) passes though the arm, but is not in close contact with the humerus in the midshaft region. The nerve is separated from the bone by the brachialis muscle. The median nerve innervates many muscles of the anterior compartment of the forearm responsible for flexion of the wrist and digits. The musculocutaneous nerve (choice D) is not in contact with the humerus. It innervates the muscles in the anterior compartment of the arm. These muscles have no function in the hand.

Answer 191

The correct answer is A. When the head of the humerus dislocates from the glenohumeral joint, it exits inferiorly, where the joint capsule is the weakest. Immediately inferior to the glenohumeral joint, the axillary nerve exits from the axilla by passing through the quadrangular space. At this location, the downward movement of the head of the humerus can stretch the axillary nerve. The axillary nerve innervates the deltoid muscle after leaving the axilla. The dorsal scapular nerve (choice B) passes along the medial border of the scapula to innervate the rhomboid muscles. The nerve does not pass in the region of the glenohumeral joint. The lateral and medial pectoral nerves (choices C and D) branch from the lateral and medial cords of the brachial plexus, respectively, and exit through the anterior wall of the axilla to innervate the pectoralis major and minor. These nerves do not pass in the region of the glenohumeral joint. The suprascapular nerve (choice E) is a branch of the upper trunk of the brachial plexus and passes over the superior border of the scapula to innervate the supraspinatus and infraspinatus muscles. This nerve does not pass in the region of the glenohumeral joint.

Answer 192

The correct answer is B. A right dominant coronary circulation is present when the posterior descending branch originates from the right coronary artery (80% of individuals). On the contrary, the posterior descending artery originates from the left circumflex artery in a left dominant circulation (20% of individuals). The posterior descending branch gives blood to the posterior half of the interventricular septum. Occlusion of the left circumflex artery in a left dominant circulation will therefore lead to ischemic necrosis in the left ventricular wall and the posterior interventricular septum. The apex of the left ventricle (choice A) is dependent on the anterior descending branch; thus, occlusion of the left circumflex does not affect this portion of the left ventricle. Infarction of the lateral (free) wall alone (choice C) will result from occlusion of the circumflex in a right dominant circulation. An isolated infarct of the posterior interventricular septum (choice D) arises from occlusion of the posterior descending branch. Isolated infarcts of the right ventricular wall (choice E) are very rare and would be caused by occlusion of branches of the right coronary artery.

Answer 193

The correct answer is E. At this level, the lateral portion of the dorsal columns (funiculus) is composed of the fasciculus cuneatus. Axons carrying tactile, proprioceptive, and vibratory information from the ipsilateral arm enter the spinal cord via the dorsal root, ascend the cord in the fasciculus cuneatus, and synapse in the nucleus cuneatus of the caudal medulla. Secondary neurons from this nucleus give rise to internal arcuate fibers, which decussate and ascend to the thalamus (ventral posterolateral nucleus, VPL) as the medial lemniscus. Tertiary neurons from the VPL project to the ipsilateral somatosensory cortex. Because the fibers that carry this information do not cross until they reach the medulla, damage to the fasciculus cuneatus would result in a deficit in tactile, proprioceptive, and vibratory sense in the ipsilateral arm. Fine motor control of the fingers (choice A) would be carried principally by the ipsilateral lateral corticospinal tract in the lateral funiculus of the cord. Motor control of the contralateral foot (choice B) is carried by the ipsilateral corticospinal tract in the lateral funiculus of the cord. Hemianhidrosis (lack of sweating) over half of the face (choice C) could be produced by interruption of sympathetic innervation to the face, which projects from the hypothalamus to the intermediolateral cell column at levels T1 and T2. It descends in the lateral funiculus of the cord. Interruption of this tract results in Horner's syndrome (miosis, ptosis, and hemianhidrosis). Proprioception from the ipsilateral leg (choice D) is carried by the fasciculus gracilis in the medial part of the dorsal columns.

Answer 194

The correct answer is A. Tumors of the ventricular system of the brain can affect the brain tissue either directly, via pressure on or invasion into a physically close structure, or indirectly, by obstructing cerebral spinal fluid (CSF) flow and causing hydrocephalus. The caudate nucleus is a C-shaped structure that composes part of the wall of the lateral ventricle throughout its extent. The only structure listed that is adjacent to the body of the lateral ventricle and would therefore be directly affected by the large tumor described in the question is the caudate nucleus. Anatomically, the caudate nucleus has a massive head and a slender curving tail that follows the curve of the lateral ventricle. The head of the caudate nucleus lies superior to the lentiform nucleus. The cerebellum (choice B) overlies the fourth ventricle. The hippocampus (choice C) is adjacent to the inferior (temporal) horn of the lateral ventricle. The hypothalamus (choice D) abuts the third ventricle. The pons (choice E) forms part of the floor of the fourth ventricle.

Answer 195

The correct answer is D. Nondisjunction can occur in both meiosis and mitosis and refers to a failure of paired chromosomes to separate and go to different daughter cells. When this happens, one daughter cell gets an extra chromosome, and the other daughter cell is "short" one chromosome. A balanced translocation (choice A) is an exchange of genetic material between nonhomologous chromosomes that preserves all critical genetic material. Chromosomal breakage (choice B) produces fragmented chromosomes and can contribute to tumorigenesis. Fertilization by two sperm (choice C) produces triploidy and is seen in many spontaneously aborted fetuses. An unbalanced translocation (choice E) occurs when nonhomologous chromosomes exchange genetic material with a net loss or gain of critical genetic material.