Download Dissection of the Sheep Brain

Dissection of the Sheep Brain
Laboratory Objectives
After completing this lab, you should be able to:
1. Identify the main structures in the sheep brain and to compare them with those of the
human brain.
2. Identify and locate the main structures in the human brain by viewing an actual human
brain from a cadaver using Anatomy & Physiology Revealed, Version 2.0 CD.
3. Describe the functions of the main structures of the sheep brain and human brain
discussed in lab.
4. Identify the cranial nerves and describe their functions.
INTRODUCTION
The human brain is the largest and most complex organ of the nervous system. It weights about 3
pounds in an average adult and is mainly composed of nervous tissue. It is made up of about 100
billion neurons and approximately 900 billion neuroglia cells. The brain is responsible for body
sensations and perception, initiates and coordinates muscle contractions and body functions, and
carries on higher mental abilities, such as thinking, memory, etc. The brain is divided in four
parts: (1) cerebrum; (2) brainstem, which consist of midbrain, pons, and medulla oblongata; (3)
diencephalon, which consists of the thalamus and hypothalamus; and (4) cerebellum.
Twelve pairs of cranial nerves arise from the underside of the brain: 2 pairs arise from
the cerebrum and 10 pairs of cranial nerves arise from the brainstem. These cranial
nerves are designated by numbers and names. The number indicates the order in which
the nerve arises from the brain, form anterior to posterior. The name comes from the
primary functions or general distribution of the cranial nerve.
In this laboratory, you will dissect the main parts of the sheep brain. Most of these
parts are similar in structure to the human brain while some are not. However, the sheep
brain is an excellent organ used to understand the mammalian brain structures and
functions. Therefore, the parts of the sheep brain that you will dissect will be compared
with those of the human brain in structure and function. You will also identify parts of
the human brain by viewing an actual brain from a cadaver by using your Anatomy &
Physiology Revealed, Version 2.0 CD.
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Procedure
PART A
NOTE: use TABLE 1.1 to describe functions and appearance
or characteristics for each part of the sheep brain that you
dissect.
Meninges, Cerebrum, Cerebellum & Spinal Cord
1. Obtain a preserved sheep brain.
2. Examine the surface of the sheep brain for the presence of meninges. Most likely you
will only see the pia mater as the outermost layers (dura mater and arachnoid mater)
were lost in the removal process of the sheep brain from the cranial cavity.
Dura Mater
Use the pointed prove to
pick a piece of pia mater at
several parts of the brain
and also at the spinal
cord.
Pia Mater
Sheep Brain
3. Position the sheep brain with its anterior surface on the dissecting tray. Locate the
following structures:
Cerebrum
Cerebellum
Spinal Cord
Posterior View
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PART B
Cerebrum
1. With the sheep’s brain anterior surface on the dissecting tray, identify and locate the
longitudinal fissure, the 2 cerebral hemispheres (right and left cerebral hemispheres),
and the transverse fissure.
Longitudinal Fissure
Left Cerebral
Hemisphere
Use the blunt prove to
pierce through the pia mater
at the surface of the
longitudinal fissure. Notice
that the 2 fissures you are
observing are deep grooves.
Right Cerebral Hemisphere
Transverse Fissure
Spinal Cord
Posterior View
2. Identify gyri and sulci at the cerebrum of the sheep brain.
Gyrus = singular
Gyri = plural
Sulcus = singular
Sulci = plural
Gyri
Sulci
How are gyri of the human brain
different from the ones on the sheep’s
brain? ________________________
_____________________________
_____________________________
_____________________________
_____________________________
Use the blunt prove to
pierce through the pia
mater on the surface of
sulci. Notice that sulci are
shallow grooves.
Posterior View
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3. The cerebrum is divided in 5 lobes: Frontal, Parietal, Temporal, Occipital, and Insula.
In the lab you will only locate and identify the following 4 lobes of the cerebrum:
Frontal Lobe-lateral view
Parietal Lobe-lateral view
Temporal Lobe-lateral view
Occipital Lobe-lateral view
NOTE: Do other views of the sheep brain to identify lobes: superior, inferior views
4. Grab the cerebrum and the cerebellum and GENTLY bend downward the two of them.
This will expose the corpora quadrigemina (four rounded structures that make up the
midbrain of the brainstem). Notice that on the superior portion of the corpora
quadrigemina you will see the pineal gland.
Pineal Gland
Cerebrum
Midbrain
Cerebellum
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5. With the anterior portion of the sheep’s brain on the dissecting tray, CAREFULLY
remove a slice from the parietal lobe using the scapel. Notice the white matter (cerebral
medulla) and the gray matter (cerebral cortex) of the cerebrum.
cerebral cortex
(gray matter)
?
What structure or structures of the neuron are
found in the gray mater of the cerebrum?
What structure or structures of the neuron are
found in the white matter of the cerebrum?
cerebral medulla
(white matter)
Which matter makes up the MAIN bulk of
the cerebrum?
Posterior View
6. Using the figure below:
A. LABEL: cerebral cortex, cerebral medulla, gyri, cerebrum and cerebellum.
B. DRAW: 1) the structures or parts of the neuron found in the cerebral cortex.
2) the structure or part of the neuron found in the cerebral medulla.
NOTE: review the three (3) main structures of the neuron in Figure 10.1,
pg. 355, of your A&P textbook.
? Circle One:
a) The cerebral medulla is
made of white/gray matter.
b) The cerebral cortex is
made of white/gray matter.
c) Does the cerebellum have..
white matter? Yes No
gray matter? Yes No
Posterior
Anterior
Midsagittal Section of the Human Brain
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7. Position the sheep’s brain on the dissecting tray with its anterior surface upward.
Identify the following structures:
Olfactory nerve (bulb)
Longitudinal fissure
Olfactory tract
Optic chiasma
Optic nerve
Optic tract
Midbrain
Pons
Medulla oblongata
Spinal cord
Anterior View
PART C
Brainstem: composed of the midbrain, pons, and medulla
oblongata
1. Position the sheep’s brain on the dissecting tray with its anterior surface upward.
Identify the three structures that make up the brainstem.
Midbrain
Pons
Medulla oblongata
Anterior View
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Brainstem
2. Position the sheep brain with its anterior surface on the dissecting tray. Using the
scalpel CAREFULLY cut the sheep brain along the longitudinal fissure and continue
then through the midline of the cerebellum and spinal cord to produce a midsagittal
section of the brain and spinal cord.
Longitudinal Fissure
3. Locate the following parts in the midsagittal section of the sheep brain.
Cerebrum
Pineal Gland
Corpora quadrigemina of midbrain
Cerebellum
Spinal cord
Optic nerve
Midbrain
Pons
Medulla oblongata
Brainstem
Midsagittal Section
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PART D
Diencephalon: composed of Thalamus and Hypothalamus
1. Locate the 2 structures that make up the diencephalon in the longitudinal section of the
sheep brain.
Thalamus
Diencephalon
Hypothalamus
Midsagittal Section
PART E
Cerebrum: Revisited!
1. Identify the following structures found in the cerebrum.
Corpus callosum
Use your blunt prove
and insert it inside
the corpus callosum
to find the lateral
ventricle.
Lateral ventricle
(cavity)
Midsagittal Section
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PART F
Cerebellum
1. Identify the gray matter (cerebellar cortex) and white matter (cerebellar medulla) of
the cerebellum.
Cerebellar cortex (gray matter)
Cerebellum
Midsagittal Section
Cerebellar medulla (white matter)
Note: the white matter pattern
in the cerebellum is called
arbor vitae.
?
What structure or structures of the neuron are found in the gray matter of the cerebellum?
What structure or structures of the neuron are found in the white matter of the cerebellum?
2. LABEL: cerebellum, cerebellar cortex, and cerebellar medulla in this midsagittal
section
the human
Whichofmatter
makesbrain.
up the main bulk of the cerebellum?
Posterior
Anterior
Midsagittal Section of the Human Brain
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Exercises
1. LABEL: the structures in this midsgittal section of the right half of the human brain.
E
A. _____________________________
F
B . _____________________________
C. _____________________________
A
D
J
D. _____________________________
E. _____________________________
B
C
G
F. (cavity)_______________________
G. _____________________________
H
K
L
H. _____________________________
I. ______________________________
I
Anterior
M
Posterior
J. ______________________________
K. _____________________________
L. (fissure)_______________________
M. _____________________________
2. LABEL: the lobes of the human cerebrum.
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3. IDENTIFY: write the name of the brain structures or parts described below.
______________a) A mass of white fibers connecting the left and right cerebral
hemispheres.
______________b) A fold of cortical gray matter on the surface of the cerebrum
______________c) The middle of three divisons of the brainstem.
______________d) The gray matter on the surface of the cerebrum.
______________e) The gray matter on the surface of the cerebellum.
______________f) The white matter on the cerebrum.
______________g) The white matter on the cerebellum.
______________h) Fissure dividing the cerebrum and the cerebellum.
______________ i) Area where the optic nerves cross.
4. LABEL: the structures of the brain by placing the correct name next to the spaces
provided.
Skull
Meninges
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