Brain

Question 1

Describe the Brain

Answer 1

one of the larger organs of the body - approximately 1300 grams

Question 2

Brain Stem (4)

Answer 2

A. Inferior “stalk” of the brain.
B. If brain were thought of as a mushroom this would be the stem.
C. Superior (rostral) continuation of the spinal cord.
D. Made up of: medulla oblongata, pons, and the midbrain.

Question 3

Cerebrum - Diencephalon (2)

Answer 3

A. Region just superior to the midbrain of the brainstem.

B. Made up of: Thalamus and Hypothalamus

Question 4

Cerebrum - Telencephalon (3)

Answer 4

A. The largest part of the brain in humans (about 7/8’s of the total brain weight) usually much smaller relative to total brain size in lower animal forms.
B. Two large hemispheres which mushroom out over the rest of the brain.
C. Seat of our intellect (seat of our soul??)

Question 5

Cerebellum (3)

Answer 5

A. Also especially large in the human brain.
B. Two large lobes inferior to cerebral hemispheres on the dorsal part of the brainstem.
C. Involved in coordinated movement, posture, equilibrium, etc..

Question 6

Cerebrospinal Fluid (CSF) (5)

Answer 6

A. Circulates in subarachnoid space and within the ventricles of the brain and the central canal.
B. Formed mainly by the choroid plexus in the ventricles of the brain.
Choroid Plexus - an invagination of pia mater - contains a core of very vascular connective tissue with many capillaries and a cuboidal epithelium.
C. Production of CSF is not yet completely understood.
- involves some active process by the epithelial cells of choroid plexus.
D. Volume varies from 80-200 mls, average = 130 mls.
E. Fluid is clear and colorless - contains very few cells (just a few lymphocytes - over 10/ml means disease) - low glucose and low protein content.

Question 7

Ventricles of the brain (4)

Answer 7

A. Intercommunicating cavities filled with CSF and continuous with the central canal and subarachnoid space.
B. Two lateral ventricles (one in each cerebral hemisphere) separated by a single membrane called the Septum Pellucidum.
C. Third Ventricle - slit-like ventricle, inferior to the lateral ventricles and located between the two halves of the thalamus. - communicates with the lateral ventricles via the foramen of Monroe (interventricular foramen).
D. Fourth Ventricle - space directly beneath the cerebellum on the dorsal side of the brainstem.
1. Communicates with the third ventricle via the cerebral aquaduct (aquaduct of Sylvius).
2. Most inferior (caudal) portion of the 4th ventricle flows directly into the central canal of the spinal cord.
3. Three openings in the caudal “roof” of the 4th ventricle communicate with the subarachnoid space: medial opening = Foramen of Magendie, two lateral openings = Foramina of Luschka.

Question 8

Hydrocephalus (3)

Answer 8

• an excess accumulation of CSF.
  A. External Hydrocephalus - excess fluid mainly in subarachnoid space - often found in senile atrophy of the brain.
  B. Internal Hydrocephalus - results usually from blockages of the openings in the roof of the 4th ventricle - causes fluid to accumulate within ventricles - in newborn, if skull is not yet totally formed - entire head will swell.
  C. Communicating Hydrocephalus - combination of above two.

Question 9

Blood Supply (5)

Answer 9

A. The brain gets its blood supply from two internal carotid arteries and two vertebral arteries.
B. Nervous tissue must have a constant supply of O2 (even though it actually uses less than many other tissue types). If supply is interrupted:
1. few seconds - unconsciousness
2. after 2 minutes - cells are dying
3. after 4 minutes - some irreparable damage
4. after 6 minutes - individual dies
C. Important consideration during childbirth, or for heart attach victim.
D. CNS must also receive a constant supply of glucose. Does not have the capability for storage, therefore it must be present in circulation.
E. Only some things are able to cross from the blood to the CNS because of the Blood Brain Barrier.

Question 10

Medulla Oblongata (6)

Answer 10

A. Between superior portion of spinal cord and pons.
1. about one inch long.
2. most inferior (caudal) portion of the brain stem.
B. Contains all ascending and descending tracts of the spinal cord.
C. On ventral side (anterior) one sees two tube-like formations (ridges) running vertically toward the spinal cord - these in cross section appear triangular in shape and are called pyramids.
1. The pyramids are actually a bundle of fibers running from the cortex to motor neurons in the ventral horns of the spinal cord.
2. At the most caudal extent of the medulla - these tracts cross - decussation of the pyramids - this is why right side of brain controls left side of body and left side of brain controls the right side of body.
D. On dorsal side of medulla - four bumps - two nuclei on each side - Nucleus Gracilis and nucleus Cuneatus - these nuclei are neurons which receive input from the ascending tracts - fasiculus cuneatus - fine touch, proprioception, etc. Neurons from these nuclei send fibers which cross and ascend on to the thalamus.
E. Reticular Formation - area of sort of mixed white and grey matter - contains both neurons and axons.
1. Only partially contained in medulla - spreads throughout the pons and midbrain and even into the diencephalon.
2. Functions in consciousness and arousal and has many other - as of yet - undefined functions.
3. Reticular system of medulla contains centers for regulation of heart contraction, breathing, and vasoconstriction.
F. Olives - two bumps on ventrolateral medulla - one on each side just lateral to the pyramids.
- receives fibers from many parts of CNS (both from higher and lower centers) and transmits them to the cerebellum.

Question 11

Pons Varolii (4)

Answer 11

(usually called the “pons”) - (means “bridge”)
A. Region just anterior to the cerebellum, between the medulla and the midbrain - also approximately 1 inch long.
B. Has many transversally running fibers which form a Middle Cerebellar Peduncle on each side.
C. Also has many longitudinal fibers which are made up of fibers of the ascending and descending tracts of the higher brain centers.
D. Contains a fair portion of the reticular system
- helps to regulate breathing among other things.

Question 12

Midbrain (Mesencephalon)

Answer 12

A. Located between the pons and the diencephalon.
B. Also about 1 inch long.
C. Contains the cerebral aquaduct connecting the 3rd and 4th ventricle.
D. Cerebral Peduncles - fibers descending from the brain (cortex) and ascending to the thalamus.
E. Tectum - dorsal portion
1. Contains Corpora Quadrigemina - four rounded eminences
a. two superior are called superior colliculi
b. two inferior, are called inferior colliculi
- Superior - for reflex response to visual stimuli
- Inferior - for reflex response to auditory stimuli
F. Substantia Nigra - pigmented area
1. A motor nucleus whose connections are not fully understood.
2. Normally has increased concentration of transmitter Dopamine - in Parkinsonism this is absent.
G. Red Nucleus - a major nucleus in the reticular formation of the midbrain.
- important motor nucleus (rubrospinal tract origin - muscle tone)
H. Medial Lemniscus - this is the term for the fibers from the Nuclei Gracilis and Cuneatus after they have crossed until they reach the thalamus. Actually found within the medulla pons and midbrain - fine touch, proprioception, etc. 2 pt discrimination.

Question 13

Cerebrum - Thalamus (4)

Answer 13

A. Two large egg-shaped structures between the midbrain and the cerebrum made up of various nuclei.
B. Functions mostly as a “relay station” for sensory information, whose afferent fibers synapse in the thalamus, and is then sent on to the cortex.
C. Important nuclei:
1. medial geniculate - hearing
2. lateral geniculate - vision
3. ventral posterior nuclei - general sensations
D. Some interpretation is done at the level of the thalamus - for example: Pain can be sensed by the thalamus, but without the specific areas of the cortex intact to which the pain sensation is relayed, one will not be able to localize it.

Question 14

Cerebrum - Hypothalamus (2)

Answer 14

A. Anterior and inferior to the thalamus - forms the floor and inferior lateral walls of the third ventricle - sits directly over the sella turcica of the sphenoid bone.
B. Controls many of the body’s basal functions that are vital to survival including:
1. heart rate
2. glandular secretions
3. activities of various organs
4. receives sensory info from viscera
5. principal controller of the endocrine system (esp. pituitary gland)
- set just above pituitary and is connected to it by the infundibulum.
6. controls the autonomic nervous system
7. believed to be related to certain “mind over matter phenomenon”
8. controls body temperature
9. regulates food intake (hunger)
10. regulates fluid intake (thirst)
11. also assists in maintaining patterns of sleep and awakefulness.

Question 15

Cerebrum - Telencephalon (7)

Answer 15

A. Forms the bulk of the brain
B. Inner white matter - outer gray matter = cerebral cortex
(note: opposite arrangement of spinal cord)
C. Composed of ridges and valleys called gyri and sulci respectively
D. Two hemispheres are separated by the longitudinal fissure - with the exception of a broad band of fibers connecting the two hemispheres called the corpus callosum
E. Falx Cerebri - dura mater which extends into the longitudinal fissure.
F. Lobes - each hemisphere is divided into 4 lobes
1. Frontal
2. Parietal
3. Occipital
4. Temporal
G. Central Sulcus - each hemisphere is divided almost in the middle by a sulcus called the Central sulcus. On either side of this are two gyri called the precentral and the postcentral gyrus

Question 16

White matter - consists of: (3)

Answer 16

A. Association Fibers - transmits information between gyri within the same hemisphere.
B. Commissural Fibers - transmit information from one hemisphere to another.
C. Projection Fibers - form ascending and descending tracts that transmit information to other parts of CNS.

Question 17

Basal Ganglia (cerebral nuclei) (5)

Answer 17

–nuclei deep in the cerebral hemispheres
A. largest - Corpus Striatum (some feel this is only one)
- consists of:
1. caudate nucleus
2. lentiform nucleus (lens-shaped)
a. putamen - more lateral portion
b. globus pallidus - more medial portion
B. other nuclei
1. claustrum - thin line of gray matter between putamen and lateral cortex
2. amygdaloid - almond-shaped nucleus at the tip of the caudate in the temporal lobe.
C. Basal ganglia are interconnected with many parts of CNS.
D. Functions are not totally understood.
1. For one thing - believed to be involved with subconscious movement of skeletal tissue - e.g. multiple movements during walking.
2. Influences movement via “extrapyramidal” connections.
E. Damage may produce involuntary movement of skeletal muscle or tremor
- damage to a large portion of the caudate nucleus will result in paralysis of the opposite side.

Question 18

Limbic System (10)

Answer 18

A. Components include:
1. Limbic Lobe - two gyri of the cerebral hemispheres
a. Located inferiorly and medially in cerebrum is the cingulate gyrus
b. Located posterior to the corpus callosum and diencephalon is the parahippocampal gyrus or hippocampal gyrus.
2. Hippocampus
- located just medial to temporal horn of the lateral ventricle.
3. Amygdaloid nucleus
- located in temporal horn at the tip of the tail of the caudate nucleus
4. Hypothalamus -
- located inferior to the thalamus and anterior to the midbrain
5. Anterior Nucleus of the Thalamus
- anterior portion of thalamus
B. System appears to encircle the diencephalon and upper part of the brainstem.
C. Controls the emotional aspects of our brain that are important in our survival.
1. Keep in mind that behavior is a very complex and involved aspect of our physiology and is controlled (at least in part) by almost all parts of the nervous system.
2. Limbic system apparently is involved in the more involuntary aspects of behavior.
- those aspects which the Christian struggles so hard to control (Biblical - desires of the flesh)
- in lower animal forms - appears to play a much greater role in behavior.
D. Appears to be associated with our perception of pleasure and pain (reward and punishment)
1. Stimulation of certain areas - pain
2. Stimulation of other areas - pleasure
E. Appears to control rage and docility feelings - our feelings of anger - although usually controlled by “higher” centers - have their origins in the limbic system.
F. Involved in our feelings of fear.
G. Involved in feelings of sorrow - “emotional pain” is felt within the limbic system.
H. Sexual drives and desires are directed within the limbic system.
I. Emotional responses to sensations like taste or smell.
J. Feelings of love.

Question 19

Functional Divisions of the Cerebral Cortex (5 huge)

Answer 19

A. These can be classified into 3 basic categories:

1. Sensory Areas - which interpret all of one’s sensory input (sight, sound, touch, pain, taste, etc.)
2. Motor Areas - control of the body’s musculature (movement and posture)
3. Association Areas - include the intermediate areas between sensory input and motor output.
   - these tend to involve all of one’s emotional and intellectual processes.

B. Areas of specific function were first mapped and assigned numbers around the turn of the century by a scientist named K. Brodmann. Today the cerebrum is still described in relation to “Brodmann’s numbers.”

C. Sensory Areas
1. The ultimate termination of impulses for (General Sensory Area) G.S.A. (general somatic afferents) is an area just posterior to central sulcus - called postcentral gyrus.
a. This corresponds to sensations like pain, touch, and temperature sensation
b. Within this postcentral gyrus - all parts of the body are represented according to the number of receptors in the region. For example the lips have a disproportionately large area in the cortex because of their many sensory receptors. So a map can be drawn of the entire body from the areas in this gyrus, but parts will be out of proportion to their actual size.
2. Somesthetic Association Area (or sensory association area)
a. Immediately posterior to the post central gyrus
b. Integrates and interprets sensations
c. Example - can interpret the shape of an object by its feel and associate it with stored information about similar objects. Like how you find your car key in your pocket.
3. Primary Visual Area
a. Most posterior aspect of cerebrum and occipital lobe
b. Courses along fissure on medial portion of occipital lobe - calcarine fissure
c. Distinguishes shapes and colors
4. Visual Association Area
a. Area immediately surrounding the primary visual cortex in the occipital lobe
b. Allows one to recognize and evaluate what is seen (relates to previous visual experiences)
5. Primary Auditory Area
a. Located on superior portion of temporal lobe
b. Distinguishes volume, pitch, rhythm, tone, etc.
6. Auditory Association Area
a. Surrounding areas 41 and 42 on lateral superior portion of the temporal lobe.
b. Interprets sounds as to meaning (examples: changes words to thoughts, identifies music, recognizes noises, etc.)
7. Primary Gustatory Area
a. Most inferior portion of postcentral gyrus
b. Recognizes and interprets taste
8. Gnostic Area
a. Processing area posterior to the post central gyrus in parietal lobe
b. This receives input from a large number of places - coordinate sensations
(example - sight with touch or sound)

D. Motor Areas
1. Primary Motor Area
a. Located mainly in precentral gyrus - just ahead of central sulcus
b. Similar to postcentral gyrus in that specific regions correspond to specific parts of the body - control movement of distinct muscle groups on opposite side of the body.
2. Premotor Area
a. Located in frontal lobe just anterior to the precentral gyrus
b. Important in learned motor activities that are difficult - like riding a bicycle or playing a song on an instrument without music.
c. Controls multiple muscles working together to produce a movement.
3. Frontral Eye Field Area
a. Area just anterior to the premotor area
b. Controls voluntary movement of the eyes
4. Motor Speech Area (Broca’s Area)
b. Located in frontal lobe - usually on left side - just superior to the temporal lobe - and anterior to area 6 (premotor area)
c. Directs the coordinated movements of speech including both breathing and phonation.
d. Damage to any one of the language areas may result in a specific clinical problem:
- aphasia - inability to speak
e. Other problems associated with different portions of the brain
- agraphia - inability to write (motor areas)
- word deafness - inability to understand spoken words
(may understand written) (Wernike’s area)
- word blindness - inability to understand written words (may understand spoken) (problem with connections between occipital and parietal lobes)
- dyslexia – difficulty in reading (problems with connections between occipital lobe and language areas in parietal lobe)

E. Association Areas

1. Made up of association fibers which connect various regions of the cortex with each other - e.g. intermediate regions between motor and sensory areas.
2. Form the major mass of the cerebrum.
3. When damaged by stroke - will exhibit neurological problems associated with the area that they project from - sometimes, because the fibers often travel in localized bundles - damage to a relatively small area can exhibit itself as if a larger portion of the cortex had been injured.

Question 20

Cerebellum (8)

Answer 20

A. Mass on the dorsal surface of the brainstem over the fourth ventricle.
B. Separated from the cerebrum by a sheet of Dura Mater called the tentorium cerebelli.
C. Made up of a narrower central vermis and two lateral hemispheres.
D. Like the cerebrum, the gray matter of the cerebellum is on the outside and is called the cortex.
- The folds are also called gyri.
E. When cut in longitudinal section - white matter looks like the branches of a tree. It is called the arbor vitae (tree of life)
F. Within the mass of the white matter are several clumps of gray matter called the cerebellar nuclei.
G. Connected to the rest of the CNS via 3 large fiber bundles:
1. Inferior Cerebellar Peduncle - between medulla and cerebellum (spinal cord).
2. Middle Cerebellar Peduncle - between pons and cerebellum.
3. Superior Cerebellar Peduncle – between cerebellum and midbrain
H. Function
1. Cerebellum - responsible for subconscious movement (e.g. coordination, posture, balance)
2. Although movement is directed by the cortex - it is modulated by the cerebellum which interprets the proprioceptive information and determines what stimulation of which muscles is required to complete the movement desired by the cortex.
3. Also very closely tied to afferent information from the inner ear and regulates the body’s equilibrium in response to changes in position.
- important in balance and muscle tone
4. Damage to the cerebellum (unlike the cerebrum) is evidenced on the ipsilateral side.
- often produces ataxia - loss of muscle coordination. This may exhibit itself as problems in speech, or gait or dizziness.

Question 21

Cranial Nerves (2 small)

Answer 21

• 12 pairs of nerves that originate directly from the brain and exit through foraminae of the skull.
• Identified by both Roman numerals and names.

Question 22

Cranial Nerves (Olfactory (I) )

Answer 22

• Sensory
• carries sensory information from the olfactory mucosa in the top of the nasal cavity.
• Nerve cell bodies of primary afferents in olfactory bulb

Question 23

Cranial Nerves (Optic (II) )

Answer 23

• Sensory
  
  • Impulses related to vision
  • Half of the fibers of each nerve cross in the optic chiasma to the other side.

Question 24

Cranial Nerves (Oculomotor (III) )

Answer 24

• Motor
• Motor information to muscles which move the eye - also to the ciliary muscle of the eye which controls diameter of the iris and shape of the lens.

Question 25

Cranial Nerves (Trochlear (IV) )

Answer 25

• Motor

- Smallest of the 12 - sends motor information to one of the muscles that move the eye.

Question 26

Cranial Nerves (Trigeminal (V) )

Answer 26

• Both sensory and motor
• Largest of the 12 - Has 3 branches:
  
  1. Opthalmic - supplies sensory innervation to forehead.
  2. Maxillary - sensory innervation over maxillary bones and nose.
  3. Mandibular - sensory information from area over mandible - also supplies motor innervation to the muscles of mastication.
     (note: this nerve also provides sensory information from the nasal cavity and the oral cavity.
• nerve cell bodies of this primary afferent are in semilunar (gasserian) ganglion.

Question 27

Cranial Nerves (Abducens (VI) )

Answer 27

• Motor

- Innervates another muscle which moves the eye.

Question 28

Cranial Nerves (Facial (VII) )

Answer 28

• Both Sensory and Motor
• Innervates muscles of facial expression.
• Carries sensory fibers from the anterior 2/3’s of the tongue for taste.

Question 29

Cranial Nerves (Vestibulocochlear (VIII) (Auditory)

Answer 29

• Sensory
• 2 branches:
  
  1. Cochlear Branch - brings sensory information for hearing from ear.
  2. Vestibular Branch - brings sensory information concerning equilibrium.

Question 30

Cranial Nerves (Glossopharyngeal (IX) )

Answer 30

• Both sensory and motor
• Motor information to muscles for swallowing and secretion of parotid gland.
• Sensory from taste receptors on posterior 1/3’s of the tongue - also information from the carotid sinus.

Question 31

Cranial Nerves (Vagus (X) )

Answer 31

• Both sensory and motor
• Motor to muscles of pharynx, larynx, respiratory passages, lungs, heart, esophagus, gall bladder, and G.I. tract in abdomen as far as the descending colon.
• Sensory information is from same organs.

Question 32

Cranial Nerves (Spinal Accessory (XI) )

Answer 32

• Motor

- Motor innervation to muscles which turn the head (just 2 of them) Sternocleidomastoid and Trapezius

Question 33

Cranial Nerves (Hypoglossal (XII) )

Answer 33

• Motor

- To muscles of the tongue.

Question 34

Pathology of CNS (7)

Answer 34

A. Poliomyelitis - viral infection - common in early childhood. - can spread to CNS - will result in destruction of nerve cell bodies in the anterior horn (motor neurons) and nuclei of cranial nerves. If virus spread to medulla - can cause death due to respiratory or heart failure. If in spinal cord only will cause paralysis of muscles innervated by the affected area.
B. Cerebral Palsy - like name implies - damage to cerebrum. May be caused by variety of factors: German Measles in mother in the first trimester of pregnancy. Radiation exposure to fetus (i.e. x-ray), O2 starvation before or during birth, hydrocephalus in infancy. Extent of disease depends on extent of damage. Victims often appear to be more mentally deficient than they actually are due to inadequacies in communication skills.
C. Parkinsonism - Degeneration of basal ganglia
- Uninhibited movement exhibiting itself as tremor in extremities. Patient shows lack of transmitter, dopamine. It is treated by administration of L-Dopa - precursor which crosses the blood brain barrier - only limited success.
D. Multiple Sclerosis - progressive degeneration of myelin sheaths of neurons in CNS - very common disease - often strikes between ages 20 and 40 but can occur at any age - causes “short circuiting” of impulses in CNS usually exhibited as loss of motor coordination. Cause is unknown. Severity is variable between people. Some people show very little effect while other patients may continue to get worse and some may eventually become bedridden and die.
E. Stroke - CVA - Cerebrovascular accident - a destruction of CNS tissue due to hemorrhage or embolus or thrombus.
1. Arteriosclerosis (more general term) - “Hardening of the Arteries”
- as person ages, vessel walls lose elasticity and thicken. This usually results in many very small CVA’s over a long period of time resulting in slow CNS degeneration.
a. Atherosclerosis (type of arteriosclerosis) - deposition of plaque on arterial walls - narrows lumen - decreases blood flow - causes starvation and death of areas supplied.
F. Headache
1. Extracranial - often = tension headaches. Often due to a tense contraction of muscles overlying the skull (Frontalis and Occipitalis)
2. Intracranial -very often due simply to vasodilation of blood vessels causing an increase in pressure within the CNS.
a. Migraine Headaches - associated with throbbing pain around eyes which spreads through the head. Usually begins with period of vasoconstriction. May cause temporary sensory deficits like incomplete visual field. This is then followed by vasodilation which produces the throbbing pain. More common in female adults. May be hereditary.
G. Alzheimer’s Disease – A progressive disease that destroys neurons over a period of years resulting in a decreased cortex size and progressive loss of brain function. Cause is unknown.
H. Senile Dementia – Gradual vascular compromising of blood supply to brain rendering, over time, less and less of the brain functional.