Sheep Brain Dissection

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

http://www.carolina.com/product/preserved+organisms/preserved+animals+%28mammals%29/sheep+organs/preserved+sheep+dissection.do

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

Cerebellum

Medulla

Pons

Spinal cord

Functions

Controls respiration, blood glucose levels, and heart

rhythms

Receives sensory info & sends it to the brain, but

also receives motor info from the brain and sends it

to the limbs

Involved in motor learning and timing of

movements

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?

Frontal Lobe

Temporal Lobe Parietal Lobe

Occipital Lobe

Primary Sensory Cortex

Primary Motor 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. Controls muscles of the tongue

B. Control muscles of the neck and shoulder

C. Vision

D. Eye movements; pupillary constriction

E. Eye movements

F. Eye movements

G. Smell

H. Sensations of the skin, muscles and teeth; controls biting and chewing

I. Mediates visceral sensations; Innervates larynx, pharynx, gastrointestinal and cardiovascular systems

J. Hearing and sense of balance

K. Taste and motor movements of the throat

L. 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?

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?

http://springvisualculture1b.blogspot.com/2010/04/neuron-psychologist.html

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.

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

Margaret Bell, MSU

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

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?

Lateral

Ventricle

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.