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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.
Ea rly in the developm ent of a mam malian 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), m esencephalon (the m idbra in),
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 m atter (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 (inne r white matter)
2. folia (outer g ray matter)
In adult humans (and other m am mals) the linear re lationship of forebrain to diencephalon to
brain stem is no longer as obvious. This is due to the massive growth and development of the
cerebrum wh ich dominates the bra in in terms of both anato my and physiolo gy.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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Lab Exercises
Human B rain Models.
Use your textbook, lab book, (figures and written description), word lists, and brief descriptions
give n here and your own common sense, to identify the fo llowing parts of the human brain.
The brain is covered by three mem branes, the m eninges. Th e innermost mem brane 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 m eter 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 ce rebrospina l fluid. Lo ok for dem onstration specimens tha t sho w 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 hem ispheres 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.
Po sterior to the cerebrum is the cerebellum . Th e 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.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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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. T hese cavities arise fro m the space within the em bryonic neural tube.
Th e fourth ventricle co nnects 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 e vidence 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 m ind the circulation pattern of C SF 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. A ll sensory nerves (except the olfactory) enter the thalam us, 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 visu al stim uli (pupil constriction, etc.). Th e 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.
Sh eep brains are similar in gross anatomy to the hum an brain and provide a m ore 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 abou t any structures you are unsure of.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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SHEEP BRAIN GUIDE
This guid e does not in clude all the structu res on you r w ord list th at yo u are respo nsible
for. Use the know ledge gained by studying the hum an models to figure out the rest.
A.
Meninges
Obtain one of the preserved she ep brains that is still encase d within the protective
mem branes kn own as the meninge s. The meninge s co nsist of three layers; an o uter d ura
mater, a middle arachnoid, and an internal pia m ater.
Examine the dura mater, a protective outer mem brane 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 a rachnoid a nd pia m ater.
B.
Brain Anato my - W ho le B rain
Obtain 2 or 3 whole sheep brains in a dissecting pan (some brains may be missing some
of the structures you w ill 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 alm ost 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 ca lled sulci. These increase the surface area of the cerebral cortex to allow m ore
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
high ly convoluted s urface (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 (figu re 2). This
exposes four ro unded bulges called the corpora quadrigem ina. Th e two superior colliculi
are larger than the two inferior colliculi. If you look on the midline be tween a nd just abo ve
the superior colliculi you will see a small fingerlike extension of tissue called the pineal
body or gland.
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Lab Addenum
Brain Anatomy & Dissection Guide
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Lab Addenum
Brain Anatomy & Dissection Guide
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Lab Addenum
Brain Anatomy & Dissection Guide
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Brain Anatomy & Dissection Guide
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Ca udal an d infe rior to the cerebellum note the medulla oblon gata which tape rs ou t to form
the more slender spinal cord.
Exam ine the brain fro m an inferior view (see Figure 3). At th e cranial end of th e 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 ne rvous tissue called the mam millary body. Th is
mamm illary 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 re gion s of the brain an d are
located just caudal to the hypothalamus.
Ca udal 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. De pending on the exact position of the sectioning cut you should
either see a m em brane linking the forn ix an d corpus callosum or a cavity between them.
The mem brane 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 th e two portions of th e thalamus that lie within each cerebral hem isphere. If
there appears to be a depressed area around the interm ediate mass of the thalam us, this
will be the third ventricle.
Exam ine again the midbrain structures; th e 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 fou rth ventricle.
Blockage of this passage causes the condition known as hydrocephalus.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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CJ Shuster
D.
Lab Addenum
Brain Anatomy & Dissection Guide
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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 o f synapses and cell bodies of ne urons. Th e inner white m atter 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. T he gray matter just below them on either side is the thalamus.
The m edial 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.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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Other Lab Materials.
A num ber of pre served and mou nte d h um an bra in specim ens w ill be available in lab.
Observe and study these specimens, looking especially for anatomy identified earlier on
the models and/or sheep brains.
Questio ns. Co mplete yo ur D ata/Analys is S heet.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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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.
Th e band of tissue at the base of the long itudinal or sagittal fissure tha t is the primary
nerve pathway connecting right and left cerebral hemispheres.
6.
Na me of the brain reg ion 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.
Na me of the point where the tw o optic nerves m eet 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.
Nam e of the deep fissure that separates the cerebellum from the cerebral hemispheres.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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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.
Involunta ry brain cente r that p lays a critical role in coordination of skeletal m uscle activity.
17.
Primary auditory area of cerebrum.
18. Brain cente r that is primary locatio n of such characteristics as rea son, w illpo we r, mem ory,
emotions and motivation.
19. Na me 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. W hat does it secrete?
22. Brain region that includes "vital centers" for involuntary control of heart function,
respiratory function and vasom oto r ac tivity.
CJ Shuster
Lab Addenum
Brain Anatomy & Dissection Guide
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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.
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Lab Addenum
Brain Anatomy & Dissection Guide
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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 im portance of th e fa ct that the surfa ce of th e 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?