brain anatomy - madison area technical college

CJ Shuster Lab Addenum Brain Anatomy & Dissection Guide 1

BRAIN ANATOMY(Adapted from Johnson, Weipz and Savage Lab Book)

Introduction

The brain is the largest and most complex part of the nervous system. It consists primarily of

nerve tissue, including billions of neurons and their associated neuroglia cells.

Early in the development of a mammalian embryo, the nervous system originates as a tube.

The anterior portion of that tube has a series of primary swellings: the forebrain, the midbrain,

and the hindbrain. At a later stage in development five major subdivisions are recognized:

telencephalon and diencephalon (subdivisions of the forebrain), mesencephalon (the m idbrain),

metencephalon and myelencephalon (subdivisions of the hindbrain). By birth the major regions

of the adult brain are all clearly evident. They are as follows:

A. Cerebrum (telencephalon)

1. cerebral cortex

2. white matter (inner tracts, nuclei, etc.)

B. Diencephalon

1. epithalamus

2. thalamus

3. hypothalamus

C. Brain Stem

1. midbrain

2. pons (metencephalon)

4. medulla oblongata (myelencephalon)

D. Cerebellum

1. arbor vitae (inner white matter)

2. folia (outer gray matter)

In adult humans (and other mammals) the linear relationship of forebrain to diencephalon to

brain stem is no longer as obvious. This is due to the massive growth and development of the

cerebrum which dominates the bra in in terms of both anatomy and physiology.


Lab Exercises

Human Brain Models.

Use your textbook, lab book, (figures and written description), word lists, and brief descriptions

given here and your own common sense, to identify the fo llowing parts of the human brain.

The brain is covered by three membranes, the meninges. The innermost membrane is the pia

mater which forms a thin covering that tightly adheres to the surface of the cerebrum and other

brain regions. It would be difficult and tedious to remove pia mater from the brain. You may

assume the pia meter is present on the models, although the models have not been designed to

illustrate its presence.

The other two of the meninges are not illustrated by the models and are absent on most of the

preserved specimens available in lab. The outermost of these, the dura mater, forms a tough,

relatively opaque protective sheet. The middle of the three meninges, the arachnoid, adheres

closely to the dura. A space between the arachnoid and pia mater, the subarachnoid space,

contains cerebrospinal fluid. Look for demonstration specimens that show evidence of dura

mater.

From the outside of the brain model, locate the cerebrum and note that it is divided into left and

right cerebral hemispheres by a deep cleft, the medial longitudinal fissure. Each hemisphere is

divided into four lobes (frontal, parietal, temporal, occipital), roughly corresponding to the

overlaying bones of the skull. The surface of each hemisphere consists of a cortex of gray

matter which is folded into a series of ridges or gyri (singular = gyrus). The furrows between

gyri are called sulci (singular = sulcus). Beneath the cortex are white matter regions of the

cerebrum.

Posterior to the cerebrum is the cerebellum. The cerebellum also has an outer cortex and is

even more folded than the cerebrum. The cerebellum is concerned with the coordination of

muscular activity. It is incompletely divided into two hemispheres separated by a dorsal, central

ridge, the vermis.

Ventrally, there are 12 pairs of cranial nerves. These nerves directly enter the brain rather than

the spinal cord. Locate the optic nerves and optic chiasma, and also the olfactory bulb and

nerve. Later, make sure you locate the rest of the cranial nerves on the diagrams and models.

Locate the pituitary gland (also known as the hypophysis) on the ventral surface of the

hypothalamus. It is an important connecting link between the two great coordinating systems of

the body: the nervous system and the endocrine system.

Locate the medulla oblongata which contains centers that regulate heart beat, blood pressure,

and respiration rate. Locate the pons which contains many important nerve tracts that connect

the cerebellum with other parts of the brain and with the spinal cord.


Now, take apart the model and look at it as a sagittal section. Locate the four spaces or

ventricles within the brain which communicate with the central canal of the spinal cord and with

the subarachnoid space. These cavities arise from the space within the embryonic neural tube.

The fourth ventricle connects to the central canal of the spinal cord and also to the third

ventricle by way of a tube, the cerebral aqueduct. The lateral ventricles (first and second

ventricles, one in each brain half) are actually located behind the septum that separates the

cerebral hemispheres. On most models one cerebral hemisphere may be taken apart to view a

lateral ventricle. W ithin the lateral ventricle locate evidence of choroid plexuses, blood capillary

beds that are the major formation site of cerebrospinal fluid. There may be choroid plexuses

indicated in other ventricles as well. Picture in your mind the circulation pattern of CSF from its

formation site, through the ventricles, into the subarachnoid space surrounding the brain and

spinal cord, and ultimately to the superior saggital sinus where it is reabsorbed into the

circulatory system. Examine the demonstration model of the ventricles of the human brain.

Locate the corpus callosum which is a large band of nerve processes connecting the two

cerebral hemispheres. This structure is best seen on a sagittal section.

Locate the hypothalamus which controls many homeostatic processes including body

temperature, water balance, and food and water intake. Locate the thalamus which is a

sensory relay center. All sensory nerves (except the olfactory) enter the thalamus, and their

impulses are sent by the thalamus to the cerebrum for interpretation. Note how the thalamus

enlarges as you move laterally away from the midline.

Locate the superior and inferior colliculi (collectively known as the corpora quadrigemina) which

are parts of the midbrain. The anterior lobes, the superior colliculi, are concerned with reflex

responses to visual stimuli (pupil constriction, etc.). The posterior lobes, the inferior colliculi, are

concerned with responses to auditory stimuli.

Now that you have oriented yourself, locate all the structures outlined in you lab book and

wordlists. Start off by identifying the 4 adult regions. Then, identify any sub-regions within each

region. Lastly, identify individual structures within each region and sub-region.

Preserved Sheep Brains.

Sheep brains are similar in gross anatomy to the human brain and provide a more realistic

concept of brain tissue than a model. Use the following Shhpe Brain Guide (written

description), plus the three figures provided, to identify the indicated structures on a sheep

brain. Ask your instructor about any structures you are unsure of.


SHEEP BRAIN GUIDE

This guide does not include all the structures on your wordlist that you are responsible

for. Use the know ledge gained by studying the human models to figure out the rest.

A. Meninges

Obtain one of the preserved sheep brains that is still encased within the protective

membranes known as the meninges. The meninges consist of three layers; an outer dura

mater, a middle arachnoid, and an internal pia mater.

Examine the dura mater, a protective outer membrane composed of a tough dense

connective tissue. Describe the appearance and feel of this membrane.

Examine the surface of the brain where the dura mater has been cut away and note the

thin filmy membrane covering over the actual brain tissue. This is more delicate tissue of

the arachnoid and pia mater.

B. Brain Anatomy - Whole Brain

Obtain 2 or 3 whole sheep brains in a dissecting pan (some brains may be missing some

of the structures you will be studying).

Examine the brain from a superior view (see Figure 1). Note the two large cerebral

hemispheres that constitute the cerebrum and envelop most of the brain. The cerebral

hemispheres are almost completely separated by a deep longitudinal or sagittal fissure.

The surface of each hemisphere consists of upward folds of nervous tissue called gyri and

grooves called sulci. These increase the surface area of the cerebral cortex to allow more

complex interaction between neurons. If you gently spread the hemispheres apart, you

can see a band of tissue that connects the two hemispheres medially. This is the corpus

callosum.

Next locate the cerebellum just caudal to the cerebrum. It is separated from the cerebral

hemispheres by a deep transverse fissure. Like the cerebrum, the cerebellum has a

highly convoluted surface (gyri and sulci).

The dorsal portion (or "roof") of the midbrain can be examined by carefully spreading

apart the transverse fissure that separates the cerebrum and cerebellum (figure 2). This

exposes four rounded bulges called the corpora quadrigemina. The two superior colliculi

are larger than the two inferior colliculi. If you look on the midline between and just above

the superior colliculi you will see a small fingerlike extension of tissue called the pineal

body or gland.


Caudal and inferior to the cerebellum note the medulla oblongata which tapers out to form

the more slender spinal cord.

Examine the brain from an inferior view (see Figure 3). At the cranial end of the brain

note the two olfactory bulbs that lay against the undersurface of the cerebrum. The band

of tissue extending caudally from these bulbs are the olfactory tracts.

Caudal to the olfactory bulbs and tracts is the X-shaped optic chiasma. This is the point

where the two optic nerves from the eyes meet and partially cross over before forming the

optic tracts that extend back to the visual area of the cerebrum.

Caudal and inferior to the optic chiasma is a small bean-shaped pituitary gland. This is a

major endocrine gland and is attached to the brain by a slender stalk called the

infundibulum. The pituitary gland may be missing from some of the preserved brains,

leaving only the infundibulum as shown in Figure 3.

The infundibulum is rooted in a bulge of nervous tissue called the mammillary body. This

mammillary body and the nervous tissue superior to it comprise the brain region known as

the hypothalamus. A portion of the pituitary gland is actually an extension of this

hypothalamus.

The ventral portion (or "floor") of the midbrain consists of the cerebral peduncles. These

bands of nervous tissue connect the cerebrum with other regions of the brain and are

located just caudal to the hypothalamus.

Caudal to the midbrain is the hindbrain which consists of the pons varioli and the medulla

oblongata. The nervous tissue then tapers to form the spinal cord.

C. Brain Anatomy - Sagittal Section

Obtain 2 or 3 half-brains formed by sagittal sectioning the preserved sheep brains.

Using Figure 4 as a guide locate the corpus callosum, the band of tissue that connects the

two cerebral hemispheres. Also locate the band of tissue below the corpus callosum

known as the fornix. Depending on the exact position of the sectioning cut you should

either see a membrane linking the forn ix and corpus callosum or a cavity between them.

The membrane is the septum pellucidum which separates two cavities, the lateral

ventricles, where cerebrospinal fluid is produced and circulated.

Inferior to the fornix is a round structure called the intermediate mass. This is the medial

portion of the two portions of the thalamus that lie within each cerebral hemisphere. If

there appears to be a depressed area around the intermediate mass of the thalamus, this

will be the third ventricle.

Examine again the midbrain structures; the dorsal corpora quadrigemina and pineal body,

and the ventral cerebral peduncles. Also re-examine the parts of the hindbrain; the pons,

the medulla, and the cerebellum. Note that there is a slender canal that passes through

the midbrain to the cavity between the cerebellum and the medulla. The cavity is the

fourth ventricle of the brain and the canal is the cerebral aqueduct. The cerebral

aqueduct carries cerebrospinal fluid from the third ventricle to the fourth ventricle.

Blockage of this passage causes the condition known as hydrocephalus.


D. Brain Anatomy - Frontal Section

Obtain one of the preserved sheep brains that has been frontally sectioned.

Examine the cerebral hemispheres and note that the outer layer, the cerebral cortex, is a

darker color than the inner tissue of the cerebrum. The darker tissue is called gray matter

and is indicative of synapses and cell bodies of neurons. The inner white matter is

indicative of myelinated axons and dendrites. Note again the gyri and sulci of the

cerebrum. The corpus callosum that links the two hemispheres, and the deep longitudinal

fissure.

Note the cavities in each cerebral hemispheres just below the corpus callosum. These

are the lateral ventricles. The gray matter just below them on either side is the thalamus.

The medial link between the two halves of the thalamus is the intermediate mass.

Depending on where the frontal section was made, you may also see a portion of the

pituitary gland or optic chiasma or tracts. You may also see the third ventricle on the

midline below the lateral ventricles.


Other Lab Materials.

A number of preserved and mounted human brain specimens w ill be available in lab.

Observe and study these specimens, looking especially for anatomy identified earlier on

the models and/or sheep brains.

Questions. Complete your Data/Analysis Sheet.


DATA/ANALYSIS SHEET

1. Beginning with the outside layer, the names of the three meninges that enclose the CNS.

2. Name the three major regions of the Diencephalon.

3. Name the three major regions of the midbrain.

4. Name the two major regions of the cerebrum

5. The band of tissue at the base of the longitudinal or sagittal fissure that is the primary

nerve pathway connecting right and left cerebral hemispheres.

6. Name of the brain region to which the pituitary gland is attached. Part of the pituitary

(posterior lobe) is actually formed from tissue of this part of the brain.

7. Name of the small cavity around the intermediate mass of the thalamus which contains

CSF.

8. Name of the point where the two optic nerves meet and partially cross over, before

passing to the cerebrum.

9. Name of the outer layer of each cerebral hemisphere.

10. The region of the brain consisting of two major hemispheres.

11. Name of the deep fissure that separates the cerebellum from the cerebral hemispheres.


12. Name of the folds of nervous tissue characteristic of each cerebral hemisphere.

13. Name of the small cavity between the cerebellum and the medulla which contains CSF.

14. Name of the cavities on either side of the septum pellucidum which contain CSF.

15. Name of the grooves characteristic of each cerebral hemisphere.

16. Involuntary brain center that p lays a critical role in coordination of skeletal muscle activity.

17. Primary auditory area of cerebrum.

18. Brain center that is primary location of such characteristics as reason, willpower, memory,

emotions and motivation.

19. Name the ridges of tissue anterior and posterior to the central sulcus of the cerebrum.

W hat are their functions?

20. W here are all motor areas of cerebrum found?

21. Name the gland that is found in the epithalamus. What does it secrete?

22. Brain region that includes "vital centers" for involuntary control of heart function,

respiratory function and vasomotor activity.


23. Brain center that regulates body temperature via control of vasomotor activity, sweating

and shivering.

24. Brain center that functions as the "master gland" of the endocrine system.

25. Primary visual area of cerebrum.

26. Brain center that acts as a primary organizational control center for all information

entering the cerebrum.

27. Brain center that includes involuntary centers critical to maintenance of muscle tone,

equilibrium and posture.

28. Speech is centered in this lobe of the cerebrum.

29. W here are all the sensory areas of cerebrum.

30. W hat is the white matter of the cerebellum ccalled?

31. Describe, in your own words, the appearance and feel of the dura mater of the preserved

sheep brain.


32. How do the relative sizes of the cerebral hemispheres compare in the sheep brain and the

human brain? W hat conclusions can you draw from this?

33. How do the relative sizes of the olfactory bulbs compare in the sheep brain and the

human brain? W hat conclusions can you draw from this?

34. W hat is the importance of the fact that the surface of the cerebral hemispheres is highly

convoluted?

35. W hat is the importance of the corpus callosum?

36. W hat is the importance of the ventricles of the brain?

brain anatomy - madison area technical college

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