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Sheep Brain Dissection
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Michigan State University Neuroscience Program
Brain Bee Enrichment Workshop
October 6, 2012
Material and information from this handout was adapted from the following sources:
Barnard College: http://bc.barnard.edu/%7Ektaylor/Neuroanatomy.pdf
Neuroscience: Exploring the Brain, Bear et al., 2007
The Sheep Brain: A Basic Guide, Cooley & Vanderwolf, 1979
BrainFacts.org
Introduction to anatomical terms
Dorsal (Latin: dorsum = back): the top of the brain
Ventral (Latin: venter = belly): the underside of the brain
Anterior: front of the brain
Posterior: back of the brain
Coronal cuts: parallel to the anterior/posterior axis
Horizontal cuts: parallel to the dorsal/ventral axis
Medial: towards the midline
Lateral: towards the side
Sagittal cuts: parallel to the medial/lateral axis
Surface structures of the brain
There are many structures of the brain that can be identified on the surface of the brain. Locate
the structures below (illustrated on the following page) and try to identify the functions of such
areas. **Be sure to ask your volunteer to help you if you need help associating functions to
different brain areas.
Sulcus (plural: sulci); the hills
Gyrus (plural: gyri); the valleys
Medial longitudinal fissure
Central sulcus (aka Sylvian fissure)
Cerebrum
Match the following structures with their functions:
Structures
Functions
Cerebellum
Controls respiration, blood glucose levels, and heart
rhythms
Medulla
Receives sensory info & sends it to the brain, but
also receives motor info from the brain and sends it
to the limbs
Pons
Involved in motor learning and timing of
movements
Spinal cord
Includes tracts that conduct signals from the
cerebrum down to the cerebellum and medulla, and
tracts that carry the sensory signals up into the
thalamus
Olfactory bulbs – What is the function of the olfactory bulbs? Compare the size of the olfactory bulbs in a
sheep relative to the total brain size compared to the olfactory bulbs in a human brain. What could account for
the size differences in the olfactory bulbs when comparing different species?
Primary Motor Cortex
Parietal Lobe
Temporal Lobe
Occipital Lobe
Frontal Lobe
Primary Sensory Cortex
The cerebral cortex can be divided into 4 lobes. Identify each of these lobes and associate the
different functions listed below with the correct lobe of the brain (each lobe many have multiple
functions from the list).
A. Processing auditory information
B. Initiating and coordinating motor movements
C. Processing sensory information
D. Problem solving and planning
E. Visual processing
F. Attention and Language
G. Personality
H. Short-term memory and learned emotional responses
Frontal lobe
A portion of the frontal lobe is defined as the primary motor cortex. Locate this structure on the sheep
brain. What is the role of the motor cortex?
Parietal lobe
A portion of the parietal lobe is defined as the primary sensory cortex What would happen if we were
to electrically stimulate this area in a sheep that was alive?
The entire surface of the body is represented in the primary sensory cortex. Interestingly, some parts of the
body have more cortical space that others. The figure below (right) is known as the homunculus and illustrates
what the body would look like based on the amount of cortical space devoted to each body region (larger body
regions have more cortical space). What parts of the body do think are more sensitive to touch based on this
figure?
Occipital lobe
Temporal lobe
Ventral view of the brain
Mammals have 12 pairs of cranial nerves. Some of these nerves are sensory nerves, other are
motor nerves, and some are both sensory and motor (mixed). Locate these 12 nerves on your
sheep brain, match each function with its associated nerve, and circle whether each nerve is
sensory, motor, or both.
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
Controls muscles of the tongue
Control muscles of the neck and shoulder
Vision
Eye movements; pupillary constriction
Eye movements
Eye movements
Smell
Sensations of the skin, muscles and teeth; controls biting and chewing
Mediates visceral sensations; Innervates larynx, pharynx, gastrointestinal and cardiovascular systems
Hearing and sense of balance
Taste and motor movements of the throat
Taste, movements of the face, winking, smiling, secretion of tears
I.
Olfactory Nerve – What would happen if we were to damage the olfactory nerve in a living sheep?
(Sensory/Motor/Mixed)
II.
Optic Nerve – You may notice that each optic nerve (containing axons of ganglion cells from a
single eye) converge at the optic chiasm. What is happening here? (Sensory/Motor/ Mixed)
III.
Oculomotor Nerve – Based on the naming of this nerve, what do you think the function is?
(Sensory/Motor/ Mixed)
IV.
Trochlear Nerve – (Sensory/Motor/ Mixed)
V.
Trigeminal Nerve – (Sensory/Motor/ Mixed)
VI.
Abducens Nerve – (Sensory/Motor/ Mixed)
VII.
Facial Nerve – (Sensory/Motor/ Mixed)
VIII.
Vestibulo-cochlear (Auditory) Nerve – (Sensory/Motor/ Mixed)
IX.
Glossopharyngeal Nerve – (Sensory/Motor/ Mixed)
X.
Vagus Nerve – (Sensory/Motor/ Mixed)
XI.
Spinal Accessory Nerve – (Sensory/Motor/ Mixed)
XII.
Hypoglossal Nerve – (Sensory/Motor/ Mixed)
White versus gray matter
You may notice that some areas of the brain are white (e.g. optic nerve; white matter), while others are a darker
color (more ivory or gray; gray matter). What could account for these differences? Think about the different
components of a neuron (see diagram below) and how this may influence the color differences you see. Also,
many of the white structures you see are nerves. What part of the neuron makes up nerves?
http://springvisualculture1b.blogspot.com/2010/04/neuron-psychologist.html
Diseases of the nervous system: Multiple sclerosis (MS)
MS is an autoimmune disorder that is caused by the body’s own immune system attacking the myelin
sheath of axons. Why is the loss of myelin a problem?
Two common areas that are damaged in MS are the optic tract and the cerebellum. What kinds of symptoms
may patients with MS have based on this information?
Midline view of the brain
We will now be making the first cut to observe some medial structures of the brain. Place the
brain in the dissection pan and cut down the longitudinal fissure, the sulcus that marks the
separation of the left and right cerebral hemispheres. Try to make a single smooth cut down the
middle.
Margaret Bell, MSU
Identify the structures in bold and match them with their associated function (listed below)
A. “Little brain”; balance and motor learning
B. Relay station of the brain; relays sensory, spatial, and motor information to the cortex
C. Consists of the superior and inferior colliculi (receive visual and auditory information); Contains
nuclei that regulate reward mechanisms and mood
D. Receives sensory information and sends it to the brain, but also receives motor information from the
brain and sends it to the limbs
E. “Bridge”; Connects midbrain to the medulla
F. Connects the left and right hemisphere
G. Links the nervous system to the endocrine system; controls body temperature, hunger, thirst, fatigue,
sleep, & circadian rhythms
H. Autonomic functions such as respiration, heart rate, blood pressure
I. Endocrine gland; main site of melatonin production
Corpus callosum – If this structure was cut in a living sheep, what wouldn’t be able to take place?
Thalamus
Hypothalamus
Pineal body
Midbrain
Pons
Medulla
Spinal cord
Cerebellum
The ventricular system (Lateral ventricle, Third ventricle, Cerebral aqueduct, Fourth ventricle)
The brain contains multiple cavities or chambers filled with cerebrospinal
fluid (CSF). What do you think is the purpose of this fluid in the brain?
Besides filling the ventricles, CSF also surrounds the brain. Why might this
be beneficial?
http://www.neuro.sofiatopia.org/brainmind_brain.htm
Coronal Sections
Now put the two halves of the brain together to make three coronal cuts (shown below) and
locate the labeled structures.
Cut #1 - Through the anterior portion of the corpus callosum
Cut #1
Lateral
Ventricle
The caudate nucleus and putamen are part of the basal ganglia. What is the primary function
of the basal ganglia?
What neurodegenerative disease is associated with a loss of dopamine neurons that project to
the basal ganglia?
Cut #2 – Through the thalamus and hypothalamus
Cut #2
What is the function of the hippocampus? What is the name of a neurodegenerative disease
that effects this structure?
Cut #3 – Through the caudal end of the cerebrum (anterior to the cerebellum), through the
superior colliculus and in between the midbrain and the pons
Cut #3
Hippocampal formation and dorsal brainstem
Observe the sheep brain that has had the cerebellum and the caudal portion of the cerebral
cortex removed. Find the structures labeled in the figure below.