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Physiological Psychology Laboratory Manual
Dissection of the Sheep Brain
Purpose
In this exercise students will further reinforce their knowledge of the anatomy of the
sheep brain. This laboratory exercise will involve dissecting/sectioning the sheep brain and
subsequently identifying and indicating a number of subcortical structure/function relationships.
Upon completion of these exercises students should be able to identify structure/function
relationships of pinned areas on a laboratory exam. Prior to completing this activity students
should visit the sheep brain dissection guide at:
Sheep Brain Dissection Guide: http://academic.uofs.edu/department/psych/sheep/
and work through the guide to further familiarize themselves with the anatomy. Additional
online and text sources students may wish to consult before, during, and after the laboratory
exercise include:
Atlas of the Sheep Brain: http://www.msu.edu/user/brains/sheepatlas/
Sheep Brain-Anatomy of Memory: http://www.exploratorium.edu/memory/braindissection/index.html
Cooley, R.K. & Vanderwolf, C.H. (1979). The sheep brain: A basic guide. Canada: Dobbyn
Creative Printing Limited.
Rosenzweig, M.R., Breedlove, S., & Leiman, A.L. (2002). Biological psychology: An
introduction to behavioral, cognitive, and clinical neuroscience (3rd ed.). Sunderland,
MA: Sinauer Associates, Inc.
Materials
1 Sheep Brain (dura mater intact)
1 Sheep Brain (dura mater removed)
Latex Gloves
Lab Coat
Dissecting Tray
Dissecting Frame
Paper Towels
Brain Dissecting Knife
Dissecting Kit:
Scalpel
Fine Straight Forceps
Fine Curved Forceps
8 Dissecting Pins
Curved Probe
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Sharp Probe
Ruler
Atlas of the Sheep Brain: (http://www.msu.edu/user/brains/sheepatlas/)
Safety Precautions
Each sheep brain was originally fixed with a formaldehyde solution and is maintained in
a preservative called Carosafetm. This preservative is much less toxic than formaldehyde and
serves to prevent mold growth and tissue deterioration. Due to the presence of these chemicals,
students are required to wear laboratory coats and gloves at all times. Students should notify the
instructor immediately if any of these chemicals come into direct contact with their skin or eyes.
Since formaldehyde is a possible human carcinogen, students who are or may be pregnant may
opt out of participating directly in this laboratory exercise. If you experience any irritation in
your respiratory system or if you become dizzy at any point during the laboratory exercise, tell
one of your group partners immediately and get assistance leaving the room (do not stand-up by
yourself!). All food and beverages should be left outside of the classroom and students should
wash their hands thoroughly following the completion of the laboratory exercise.
Method
Dissection and Identification of Mid- and Hindbrain Structures
Carefully remove the scalpel from the dissecting kit. Place the sheep brain with
dura mater removed in the dissecting tray. Pull down on the hindbrain so that you
can see the midbrain. Separate the midbrain from the rest of the sheep brain by
cutting just above the superior colliculi. Set the remaining portions (forebrain) to
the side.
Balance the midbrain/hindbrain section on its ventral surface in the dissecting
tray. Beginning on the dorsal surface, cut the cerebellum in half, being careful
NOT to cut into the medulla or pons with the scalpel. As you near the
medulla/pons toward the ventral surface of the cerebellum you should find a large
cavity, the fourth ventricle. Pull back the two hemispheres of the cerebellum,
exposing the fourth ventricle. Remove two pins from the dissecting kit and pin
back each cerebellar hemisphere in the dissecting tray.
Identify the following structures of the midbrain and hindbrain and place a check
mark in the appropriate bullet point.
o
o
o
o
o
o
o
Cerebellar Hemispheres
Cerebellar Vermi
Folia
Arbor Vitae
Cerebellar Peduncles
Fourth Ventricle
Central Canal
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o
o
o
o
3
Superior Colliculi
Inferior Colliculi
Pons
Medulla
Separating the Two Cerebral Hemispheres and Identifying Midsagittal Structures
Place your forefinger and middle finger (of your non-dominant hand) on the left
and right hemispheres respectively. Pick up the scalpel with the other hand and
position it at the longitudinal fissure toward the posterior end of the brain. Put
slight pressure on each hemisphere by pressing down with your two fingers and
very gently draw the scalpel down the longitudinal fissure toward the anterior end
of the brain using short strokes, cutting through the remaining meninges
connecting the two hemispheres. Do not cut into the brain tissue or plunge the
scalpel into the longitudinal fissure. Continue cutting through the meninges
toward the anterior end of the sheep brain. Once completed, gently bend the
hemispheres down, opening the longitudinal fissure (do not tear the hemispheres
apart). You should be able to see the corpus callosum, a thick white band of tissue
deep within the longitudinal fissure.
Return you fingers to their original positions on the left and right hemispheres.
Place pressure on each hemisphere, insert the scalpel into the longitudinal fissure
toward the posterior end of the sheep brain and carefully separate the two
hemispheres by drawing the scalpel toward the anterior end of the brain. Arrange
each hemisphere in the dissecting tray so that the midsagittal surface is facing up.
Identify each of the following midsagittal structures and place a check mark in the
appropriate bullet point. You may also wish to label the midsagittal picture below.
o Cerebral Aqueduct
o Cingulate Gyrus
o Corpus Callosum
o Splenium
o Body
o Genu
o Hypothalamus
o Lateral Ventricle
o Pineal Body
o Septum Pellucidum
o Thalamus
o Third Ventricle
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Coronal/Frontal Dissection of the Right Hemisphere of the Sheep Brain
Place a paper towel on the laboratory table surface and arrange the dissecting
frame in the center of it. Obtain a brain-dissecting knife from your professor.
Please be extremely careful, these knives are razor sharp and may cause serious
injury if not handled with care. Set the right hemisphere of the sheep brain,
anterior tip down (midsagittal edge flush with the brain-dissecting frame) into the
dissecting frame and place the dissecting knife so that the blade rests on both
edges of the dissecting frame (parallel with the table). With a firm grip on the
posterior end of the brain, trying to keep the brain as straight as possible, draw the
knife through the brain using long smooth strokes. Do not use short choppy or
jerking strokes with the knife, as this will produce ridges in the tissue slices and
may make it more difficult to identify sub-cortical structures. Please be careful
not to strike the blade against the aluminum brain-dissecting tray. Flip the
coronal/frontal slice over so the anterior tip of the brain is facing up and place it in
the dissecting tray. Repeat this procedure until you have completely sliced the
right hemisphere and arranged the tissue sections in sequential order on the
dissecting tray. Please hold the right hemisphere very carefully as you approach
the posterior end with each successive slice. Do not risk cutting your fingers just
to get another slice of tissue. Each slice will be approximately 1/8 inch in
thickness. Listed below is a table in which you should label your slices and
indicate the cell stain section number and fiber stain section number (from the online Sheep Brain Atlas) which best match each of your sections. In addition, list
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the major subcortical anatomical structures and their general functions that you
can identify in your slices without having to stain the sections.
Slice #
Cell Stain Section #
Page #
Fiber Stain Section # Page #
Slice 1
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 2
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 3
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 4
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 5
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 6
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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Slice 7
6
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 8
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 9
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 10
________________
_____
________________
_____
Slice 11
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
________________ _____
________________ _____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 12
________________
_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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Slice 13
________________
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_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 14
________________
_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 15
________________
_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 16
________________
_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Slice 17
________________
_____
________________
_____
Identifiable Subcortical Structure/Function: __________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Sagittal Dissection of the Left Hemisphere of the Sheep Brain
Place a paper towel on the laboratory table surface and arrange the dissecting
frame in the center of it. Obtain a brain-dissecting knife from your professor.
Please be extremely careful, these knives are razor sharp and may cause serious
injury if not handled with care. Set the left hemisphere of the sheep brain, medial
surface down, in the center of the dissecting frame. Place the brain-dissecting
knife so that the blade rests on both edges of the dissecting frame (parallel with
the table). With a firm grip of the lateral surface of the brain, draw the knife
through the brain using long smooth strokes. Do not use short choppy or jerking
strokes with the knife, as this will produce ridges in the tissues slices and make it
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more difficult to identify sub-cortical structures. Please be careful not to strike the
blade against the aluminum brain-dissecting frame, as this will quickly dull the
knife. Flip the sagittal slice of tissue over so the midsagittal surface is facing up
and place it in the dissecting tray. Repeat this procedure until you have
completely sliced the left hemisphere and arranged the tissue sections in
sequential order on the dissecting tray. Please hold the left hemisphere very
carefully as you approach the lateral surface with each successive slice. Do not
risk cutting your fingers just to get another slice of tissue. Each slice will be
approximately 1/8 inch in thickness and the left hemisphere and the entire
hemisphere should provide 8-10 slices of tissue. Below are sagittal sections of the
left hemisphere of a sheep brain. Compare these with your sections and
identify/label as many structures/regions as you can.
Section 1:
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Section 2:
Section 3:
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Section 4:
Section 5:
10
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Section 6:
Section 7:
11
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Section 8:
Section 9:
12