3, 4 Overview of CNs

Question 1

Pain over chin and lower lip. She was diagnosed with dermatomal herpes zoster inflammation (shingles). Which nerve contains the virus?

Answer 1

The chin and lower lip area are supplied by the mental nerve, a branch of the inferior alveolar nerve, which is a branch of the mandibular division of the trigeminal nerve (V3)

Question 2

Patient admitted with signs of cavernous sinus thrombosis. Thrombophlebitis can spread to the cavernous sinus and involve the opthalmic branch of the trigeminal nerve. Which symptom will be present?

Answer 2

The ophthalmic branch of the trigeminal nerve (V-1) supplies sensory innervation to the eyeball, leading to pain when damaged.

Question 3

Imaging reveals a tumor at the hypoglossal canal. Which muscle will be affected?

Answer 3

A tumor at the hypoglossal canal would compress the hypoglossal nerve (CN XII) and affect the genioglossus, a muscle it supplies.

Question 4

Patient has dryness of the nasal and paranasal sinuses, loss of lacrimation, and loss of taste from the anterior two thirds of the tongue. Which structure is involved with the tumor?

Answer 4

The superior salivatory nucleus is the autonomic nucleus for the facial nerve (CN VII). PS fibers carried by the greater petrosal branch of the facial nerve are responsible for supply of the lacrimal gland and sinuses via the pterygopalatine ganglion.

The geniculate ganglion contains cell bodies for taste from the anterior 2/3rds of the tongue carried by the chorda tympani branch of the facial nerve. This branch also carries PS supply for the submandibular and sublingual salivary glands.

Question 5

MRI shows a large hematoma inferior the right jugular foramen. Examination reveals right pupillary constriction (miosis), ptosis of the eyelid and anhydrosis of the face. Which ganglia is most affected by the hematoma?

Answer 5

The superior cervical ganglion (SCG), which is the uppermost part of the sympathetic chain, supplies sympathetic innervation to the head and neck. Postganglionic sympathetic nerves usually run alongside the arteries leading into the head and neck region.

Question 6

CT scan reveals tumor in the infratemporal fossa. Examination reveals loss of general sensation from the anterior 2/3rds of tongue but taste and salivation are intact. Which nerve is affected?

Answer 6

The chorda tympani joins the lingual nerve in the infratemporal fossa and a lesion in the lingual nerve before it joins the chorda tympani would account for the loss of general sensation.

If the chorda tympani were injured, the patient would present with loss of taste from ant. 2/3rds AND decrease in saliva production.

Question 7

CT scan reveals a tumor in the brain. Right eye is directed laterally and downward, with complete ptosis of her upper eyelid and her pupil is dilated. Which structure is affected by the tumor?

Answer 7

An injury to the oculomotor nerve (CN III) would cause the eye to point downward (CN IV) and laterally (CN VI) due to the unopposed contractions of the muscles.

The oculomotor nerve also provides innervation to the levator palpebrae superioris.

The constriction of the pupil is provided by PS nerves via the oculomotor nerve.

Question 8

During neurologic examination, patient’s uvula is found to be deviated to the right. Which nerve is affected?

Answer 8

An injury to the left vagus nerve (CN X) would cause the uvula to deviate to the right. The vagus nerve innervates the musculus uvulae muscle that makes up the core of the uvula.

Question 9

Patient has difficulty coughing and swalloing. MRI scan shows tumor affecting a cranial nerve. Which nerve is most likely affected?

Answer 9

The vagus nerve is responsible for sensation in the mucosa of the larynx down to the level of the vocal folds and also motor innervation of the muscles that initiate a cough reflex and swallowing (motor).

Question 10

A physician performs a pupillary light reflex test. The integrity of which of the following nerves is being checked?

Answer 10

The optic nerve is responsible for the sensory portion and the oculomotor nerve is responsible for the motor portion.

The ophthalmic division of the trigeminal nerve provides sensory innervation to the cornea for the corneal reflex, but not the light reflex.

Question 11

Man complains of hyperacusis (sensitivity to loud sounds). Injury to which cranial nerve is responsible?

Answer 11

The facial nerve innervates the stapedius muscle, which is responsible for limiting movement of the stapes, thereby reducing the intensity of sound entering inner ear.

Question 12

A patient coughs during inspection of the external auditory meatus with a speculum. The cough results from the irritation of which nerve that innervates an area of the external auditory meatus?

Answer 12

The vagus nerve innervates a part of the external auditory meatus and can trigger a cough reflex. This is due to the referred sensation from the vestibule of the larynx which is innervated by the vagus nerve.

Question 13

Patient is diagnosed with a tumor at the base of the skull that results in a decrease in tear production. Which nerve is most likely injured?

Answer 13

The greater petrosal nerve, a PS branch of the facial nerve, provides innervation to the lacrimal gland in the orbit.

The chorda tympani provides innervation to the submandibular and sublingual glands and also taste to the ant. 2/3rds of tongue.

The lesser petrosal nerve provides PS innervation to the parotid gland.

Question 14

Patient was suffering from severe infxn of the middle ear (otitis media). Surgery resulted in the following: right corner of the mouth drooping, unable to close his right eye, food collection in his right oral vestibule. Which nerve was injured?

Answer 14

A lesion of the facial nerve is likely to lead to the symptoms described because the muscles of facial expression are paralyzed.

Question 15

Patient has hearing loss in left ear and complains of loss of taste and drooling from left side of mouth. CT scan shows a tumor compressing the nerve exiting the skull through which opening?

Answer 15

The tumor is compressing the facial nerve which runs through the internal acoustic meatus along with CN VIII. The facial nerve provides sensation of taste to the ant. 2/3rds of the tongue via the chorda tympani and also mediates all facial muscles (except mastication, which is the mandibular branch of V-3).

Question 16

Patient has loss of general sense and taste sensation from the ant. 2/3rds of the tongue. Which nerve was injured?

Answer 16

The lingual nerve is the most likely nerve damaged because there is loss of both of taste and general sensory supply, which at this point has been joined by the chorda tympani.

The chorda tympani carries only taste and does not mediate general sensation to tongue.

Question 17

Patient has rheumatoid arthritis of her temporomandibular joint (TMJ) and severe ear pain. Which nerve is most likely responsible for conducting the pain sensation?

Answer 17

The auriculotemporal nerve is a posterior branch of the mandibular division of the trigeminal nerve. It encircles the middle meningeal artery and courses medially to the TMJ and then ascends up near the auricle.

Since this nerve supplies the TMJ and skin of the external auditory canal, pain from the joint can be referred to the ear.

Question 18

The corneal reflex is tested in a patient and found to be present. Which nerve is resposible for the afferent limb of the reflex?

Answer 18

The afferent/sensory limb of the corneal (blink) reflex is carried by the nasociliary nerve, which is a branch of the ophtalmic division of the trigeminal nerve (V-1).

The facial nerve (CN VII) is the efferent limb of the corneal reflex and mediates the closing of both eyes.

Question 19

Patient complains of diplopia (double vision) when walking down stairs. A lesion of which nerve is responsible?

Answer 19

The trochlear nerve innervates the superior oblique muscle, which acts to move the pupil downward and laterally. It is the only muscle that can depress the pupil when the eye is adducted. When an individual walks down stairs, this eye motion is initiated and diplopia results if it is not functioning properly.

Question 20

Radiologic studies reveal that there was damage to the anterior inferior cerebellar artery, which resulted in a small hemorrhage of the artery at its origin from the main trunk. Which nerve is affected?

Answer 20

The ant. inf. cerebellar artery (AICA) is a major supplier of the ant. inf. portion of the cerebellum. The abducens nerve is situated at the pontmedullary junction and is most likely to be damaged following hemorrhage.

Question 21

During physical examination, the patient has lost unilateral sensation of hot, cold, pain and pressure from the front part of his tongue, but taste and salivary function are preserved. Where is the injury?

Answer 21

The lingual nerve supplies sensory innervation to the mucous membrane of the ant. 2/3rds of the tongue and PS fibers to the oral salivary glands. Injury to the lingual nerve at its origin, before it joins with the chorda tympani, will result in loss of general sensation of the tongue.

Question 22

Patient has undergone facial surgery for exicision of a malignant parotid tumor. Marked weakness is seen in the musculature of the patient’s lower lip postsurgery. Which nerve was injured?

Answer 22

The ant. division of the facial nerve passes through the parotid gland is therefore at risk during surgery of the parotid gland. The branch of the facial nerve that supplies the lower lip, the marginal mandibular branch, is the one that is injured.

Question 23

CT scan showed an abscess compressing the ophthalmic branch of the trigeminal nerve. Which would be a complaint of the patient?

Answer 23

Ophthalmic nerve (CN V-1) carries sensory branches from the eye, conjunctiva and orbital contents including the lacrimal gland.

Question 24

MRI shows a brain tumor. Patient complains that the right side of his nasal cavity is dry and irritated and he frequently uses drops in his right eye, as it is always dry. The tumor probably involves which cranial nerve nucleus?

Answer 24

Superior salivatory nucleus of the facial nerve is a visceromotor cranial nerve nucleus located in the pontine tegmentum. Preganglionic PS fibers arise from the nucleus and pass laterally to exit the pons with motor VII axons. Some of the preganglionic fibers pass to the ptyergopalatine ganglion via the greater petrosal and synpase in the pterygopalatine ganglion. Postganglionic efferent fibers travel to innervate the lacrimal and mucosal glands.

Question 25

A light is directed into the right eye of a comatose patient and the pupil constricts. This confirms which 2 nerves are intact?

Answer 25

The papillary light reflex is mediated by the afferent limb carried by the optic nerve (CN II) and the efferent limb carried by the oculomotor nerve (CN III).

This muscle is specifically innervated by the PS component of the oculomotor nerve, which has its preganglionic cell bodies at the Edinger-Westphal nucleus and postganglionic fibers at the ciliary ganglion.

Question 26

Examination of an unconscious patient reveals the right pupil is dilated and unresponsive to light. CT scan reveals a large aneurysm of the sup. cerebellar artery just after it branches off the basilar, compressing which nerve?

Answer 26

The oculomotor nerve (CN III) is the efferent limb of the pupillary reflex. It carries the parasympathetic nerve with preganglionic cell bodies in the Edinger-Westphal nucleus and postganglionic cell bodies in the ciliary ganglion and supplies the sphincter pupillae of the iris.

The oculomotor nerve is found between the sup. cerebellar artery and the post. cerebral artery.

Question 27

Examination of a patient reveals inability to abduct his right eye and an absent corneal reflex on the same side. These symptoms indicate a growth in which part of the skull?

Answer 27

The superior orbital fissure in the sphenoid bone transmits the oculomotor nerve (CN III), branches of the ophthalmic division of the trigeminal nerve (V-1), abducens nerve (VI) and ophthalmic vein.

Abduction of the eye is done by the oculomotor nerve and the ophthalmic nerve supplies sensation to the cornea and serves as the afferent limb of the corneal reflex.

Question 28

Physical examination reveals swollen palatine tonsils and a tonsilectomy is performed. Which nerve coursing along the tonsillar beds needs to be spared during surgery?

Answer 28

The glossopharyngeal nerve is located in the tonsillar bed as it runs with the stylopharyngeus muscle which it innervates.

Question 29

A doctor strokes a wisp of cotton across the patient’s left cornea with no response. The doctor then strokes the cotton across the patient’s right cornea and both eyes blink. Which nerve is damaged on the left?

Answer 29

The trigeminal nerve is the major sensory nerve of the face. It has 3 branches: ophthalmic, maxillary and mandibular. The afferent limb of the corneal reflex is via the trigeminal nerve (sensation on the eyeball) and the efferent limb is the facial nerve (closing the eye)

Question 30

A CT scan of the brain revealed a dilated branch of the basilar artery at the junction of the pons and midbrain on the right side. What might be seen in the patient?

Answer 30

The CN emerging anterolaterally at the junction of the pons and midbrain is the oculomotor (CN III). It passes between the superior cerebellar and posterior cerebral arteries. An aneurysm of the PCA could result in compression of the nerve and lead to oculomotor nerve palsy. The affected eye will be in a down and out position. The outward location of the eye is due to the intact lateral rectus (CN VI). The downward location is because the sup. oblique muscle (CN IV) is intact.