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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
Lab 7: Sheep brain, cranial nerves, and histology part 1
created by Doug Wacker (brains, cranial nerves) and Greg Crowther (histology);
revised by Greg Crowther
Today’s objectives
 Identify superficial and internal structures of a sheep brain, and link those structures to
functions.
 Identify cranial nerves (connected to a sheep brain) and holes in the cranium through
which those nerves pass.
 Slice an endocrine, reproductive, neural, or sensory cat tissue in preparation for staining
and microscopy.
Supplies/equipment
 Preserved sheep brains
 Dissection tray with blue pad
 Dissection tools
 Dissection manuals
o Mammalian Anatomy: The Cat (2nd edition/2005) by Aurora M. Sebastiani and
Dale W. Fishbeck
o Atlas and Dissection Guide for Comparative Anatomy (6th edition/2007) by Saul
Wischnitzer and Edith Wischnitzer
 Human skull models
 Pipe cleaners of 2-3 colors
 Preserved cats (previously used in Lab 1 and Lab 4)
 Cryostat (Leica CM 1860) armed with blade
o Tissue Freezing Medium
o specimen discs (≥6)
 Laptop computers (for Internet research)
 Your textbook (optional)
Pre-lab assignment
By the start of your lab section (Tuesday at 2pm, Thursday at 2pm, or Friday at 8:45am) you
should (1) print or download this lab handout, read it over, and bring it to lab; and (2) complete
the pre-lab assignment posted to Canvas.
Background
Today’s lab has two parts (or three, depending on how you count them). The bulk of the lab will
be devoted to the brain and the cranial nerves; however, we will also begin a histology exercise
to be continued in Lab 8.
In our exploration of the brain, we will use the sheep brain as a model. First you will identify
several superficially visible structures of a sheep brain. Then you will section the brain sagittally
down the longitudinal fissure (a.k.a. medial longitudinal fissure) and identify some internal
structures.
Within the general scheme of stimuli => integration => response, the brain is largely a
controller/integrator; as such, it needs to receive AND send signals. It does so via the spinal
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
cord and the cranial nerves. The 12 cranial nerves are unlike other nerves in that they connect
to the brain directly (by passing through the cranium – the part of the skull that houses the brain)
rather than via the spinal cord. As part of this lab, we will examine the various holes that the
cranial nerves traverse to enter/exit the cranium. Please note that these brains have been
preserved with chemical fixatives and should only be handled with gloves.
Histology refers to the study of tissues – “tissues” referring to an anatomic level more
macroscopic than that of a single cell, but more microscopic than that of an entire organ. In
general, biological samples are harvested from a research or clinical specimen, sliced into thin
sections, and stained to reveal overall structure and/or the presence of a specific marker, such
as a specific protein of interest (often visualized with a fluorescent tag or an antibody). Histology
is a core tool of basic physiology research and of medicine; in particular, the medical specialty
of pathology routinely uses histology to inspect biopsies for evidence of cancer or other
disorders. We have seen examples of histology in the primary literature – fruit fly brain slices in
Kayser et al. (2014) and mouse pituitary gland slices in Hasuwa et al. (2013); now it is time to
give this a try ourselves! For an overview of cryostat use, consult the following YouTube video
made by UMass-Amherst students: youtube.com/watch?v=d43LFVV3h6w. Our cryostat (Leica
CM 1860) is very similar to the one in the video (Leica CM 1850).
Histology part 1
Today’s histology work is fairly brief, but since only one group can use the cryostat at a time, we
will get it started right away. Groups that are waiting for the cryostat should work on the sheep
brain dissection while they are waiting.
1. First your table must agree on which specific endocrine, reproductive, neural, or sensory
tissue you will stain and observe. Compare the H&E images you found for your pre-lab
assignment, discuss why the nominated tissues might or might not be visually
interesting, and make your decision.
2. Obtain a specimen disc from your instructor and coat it with Tissue Freezing Medium.
3. Take a sample of the chosen tissue from one of your cats. Your sample will need to sit
within your specimen disc, which is only 25-30 mm (about 1 inch) in diameter, so keep it
small!
4. Bring your specimen disc (now loaded with Tissue Freezing Medium and your sample)
to the cryostat in the lab prep room (Discovery Hall 265). You will place your disc in one
of the cryostat’s cooling slots on the quick freeze shelf (Figure 1).
5. After one minute or less, your sample will be frozen and thus ready for slicing.
6. Insert the specimen disc into the specimen head (Figure 2).
7. Using a pencil, label a frosted microscope slide with your initials and your tissue.
8. Use the control panels to move the specimen reasonably close to the blade, and to set
the initial slice thickness to 20 µm.
9. Advance the blade using the hand crank.
10. Once the blade starts cutting into the sample, continue until each slice goes all the way
through the sample and surrounding Tissue Freezing Medium.
11. Reduce the slice thickness to 7 µm.
12. Continue slicing. Put 3 or so slices on your labeled microscope slide.
13. Put the microscope slide in the slide box in the -20 °C freezer until Lab 8.
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
Figure 1 (left): The quick freeze shelf.
Figure 2 (below): The specimen head. After
loosening the clamping screw (1), insert the shaft
of the specimen disc (3) into the location hole (2)
of the specimen head. Tighten the screw (1).
Images taken from the Leica CM 1860 manual.
Superficial structures of the sheep brain
Identify the frontal, temporal, parietal, and occipital lobes of the cerebral cortex. On the
worksheet, list one sensory modality processed by each lobe.
Name and identify the sulci/fissures that separate the temporal and frontal/parietal lobes, the
frontal and parietal lobes, and the left and right cerebral hemispheres. Identify the precentral
and postcentral gyri (plural of gyrus). What important functions do the precentral and
postcentral gyri serve? Put your answers on the worksheet!
Identify the medulla oblongata, the pons, and the cerebellum. On the worksheet, label these
structures and list one function of each. Where is the cerebellum’s vermis (“worm”)?
Viewing the top of the brain, carefully pull the cerebellum down and identify the superior
colliculus and inferior colliculus. What are their functions? Check the orange dissection
manual (Wischnitzer & Wischnitzer) for clues.
Locate cranial nerves I, II, III, V, and VI. What information do these nerves carry? What are
their names? Find the olfactory bulbs. Would you guess that human olfactory bulbs are
relatively larger or smaller than sheep olfactory bulbs? Why can’t you find a single cranial nerve
I? Identify the optic chiasm.
What is the pupillary light reflex? Which cranial nerves are involved? When one has a severe
concussion, brain swelling can create pressure on the efferent nerve, disrupting normal pupillary
responses to light. This is why doctors sometimes shine a light in your eye after a head injury.
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
Internal structures of the sheep brain
Make a complete midsagittal cut along the longitudinal fissure, bisecting the brain into two equal
halves.
Identify the following corpus callosum. Locate the splenium and genu, which are parts of the
corpus callosum. (The genu is shaped like a knee; the word genuflect means to kneel.) What
does the corpus callosum connect?
Locate the cingulate gyrus (a.k.a. cingulate cortex). Can you find the septum pellucidum?
Identify the fornix. What does it connect?
Find the thalamus, pineal body, and hypothalamus. Name one substance produced by the
pineal gland.
Find the lateral, third, and fourth ventricles of the brain. These ventricles are normally filled
with cerebrospinal fluid (CSF), which is produced by the choroid plexus (not visible) within
the walls of the ventricles. What passageway connects the lateral and third ventricles? The
third and fourth ventricles?
Locate and identify the arbor vitae (“tree”) and folia (“leaves”) of the cerebellum. Which is
primarily grey matter? White matter?
Locate the anterior and posterior lobes of the cerebellum. Can you find the flocculonodular
lobe?
Cranial nerves and the human cranium
Name and identify (on a human skull model) the holes through which cranial nerves I, II, III, V,
and VI travel. You are welcome to consult Dr. Google. Note that cranial nerve V has three
parts, each of which passes through a different hole. Use pipe cleaners to traverse these holes
(white = sensory, green = motor) and show your instructor once you’ve found them.
Clean-up
Please place your brains in the bag-lined buckets in the fume hood.
Please clean your dissection tools, pans, pads, and tables.
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
Worksheet for Lab 7: sheep brain & cranial nerves (turn in one worksheet per team)
Superficial structures of the sheep brain
1. On the diagram below (from your textbook), clearly label the four lobes of the cerebral cortex
and list one sensory modality processed by each. Also label the ventricles (lateral, third, fourth).
2. On the diagram below (from http://faculty.alverno.edu/bowneps/, which got it from
http://msjensen.cehd.umn.edu/webanatomy/, which got it from P. Cull’s Sourcebook of Medical
Illustration), clearly label the precentral gyrus and postcentral gyrus (you can color them
different colors, shade them, etc.) and list the type of information processed by each. Also label
the medulla, pons, and cerebellum and list a function of each.
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
3. Where are the superior colliculi and inferior colliculi located? List a function of each.
4. What is the pupillary light reflex? In this reflex, which cranial nerve carries the sensory input,
and which carries the motor (muscular) output?
Internal structures of the sheep brain
5. Label the following structures in the diagram below (from E.N. Marieb et al., Human Anatomy
& Physiology Laboratory Manual):
 Cingulate gyrus
● Medulla and pons
 Corpus callosum, genu, splenium
● Pineal gland
 Fornix
● Pituitary gland
 Hippocampus
● Septum pellucidum
 Hypothalamus
● Thalamus
 Inferior and superior colliculi
Some structures might not have a label line, and you will not use all label lines.
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
6. Name a substance produced by the pineal gland, and a function of this substance.
7. List two important general functions of the hypothalamus.
8. What is the overall function of the thalamus?
9. What is the overall function of the hippocampus?
10. Instructor’s initials for check of internal sheep brain structures: ______
Cranial nerves
11. Label cranial nerves I, II, III, V,
and VI on the diagram of a ventral
view of a sheep brain (taken from
E.N. Marieb et al., Human Anatomy
& Physiology Laboratory Manual).
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BBio 351: Principles of Anatomy & Physiology I
Fall 2015
12. Fill in the cranial nerve table below.
#
Name of cranial
nerve
Sensory,
Motor,
Function (brief)
or Both?
Hole(s) in cranium
I
II
III
IV
V
13. Instructor’s initials, verifying completion of pipe cleaner exercise: ______
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