Sheep Brain Dissection Picture Guide
Figure 1: Right Hemisphere of Sheep’s Brain
Figure 2: Underside of Sheep’s Brain
Figure 3: Saggital cut of Sheep’s Brain to reveal subcortical structures
Figure 4: Coronal cut of Sheep’s Brain to reveal grey and white matter
Name:__________________________________________ Section:_______ Date:___________
Sheep Brain Dissection Worksheet
In this Neuroscience Module you will learn how our neurons work together to form circuits in
the brain. You will also learn how these circuits function to regulate complex behaviors and how
these behaviors can be disrupted due to damage or disease. We will start our exploration of the
nervous system by dissecting a sheep’s brain to familiarize ourselves with key brain structures.
However, there’s no avoiding the fact that a sheep is, well, a sheep. Can you think of two brain
regions found in humans that are unlikely to be well represented in sheep? (Hint: think about
things that we do that sheep don’t.)
1.________________________________________________________
2.________________________________________________________
How about a brain region that might be better represented in sheep than humans?
1. ________________________________________________________
The Coverings of the Brain
The sheep brains we are dissecting have been preserved in fixative. A fresh brain is much more
jelly-like and susceptible to damage. The living brain is encased in fluid filled membranes or
meninges that cushion the brain within the skull and help to protect it from damage. The
meninges contain blood vessels that supply the brain with oxygen. Keeping the brain supplied
with oxygen is critical for it to function properly. When the blood supply to the brain is
disrupted, strokes occur. The meninges also contain neurons that sense pain. Pain neurons are not
found within the brain itself. Migraine headaches occur when the blood vessels in the meninges
dilate (swell) so that fluid leaks out. The pain neurons sense the fluid and mount an inflammatory
response that causes pain.
Take your scalpel and carefully strip off the meninges from the cortex. Be careful not to dig
into the cortex itself.
The Overall Organization of the Central Nervous System
Lay your sheep brain with the right side up then compare it with the photograph of the
right side of a sheep’s brain in the Sheep Brain Dissection Picture Guide.
Take a minute and sketch this view of your sheep brain in the space below.
Examine the gyri and the sulci. Are there similar numbers of gyri and sulci in your sheep brain as
in the one pictures? Are they identically placed? What does this suggest in terms of the relation
of the gyri and sulci to functional areas of the brain?
For homework, you read about how the central nervous system is organized. Make sure you can
identify each part visible on the surface of the brain. Next explain what each area does in the
table below, and label each area on your sketch above.
Brain Region
What does it do?
1. Spinal Cord
2. Cerebellum
3. Frontal lobe
4. Parietal lobe
5. Temporal lobe
6. Occipital lobe
7. Central Sulcus
The Sheep Brain Dissection Picture Guide identifies the boundaries between the lobes in a cortex
– the longitudinal fissure and the central sulcus. Can you identify the boundaries between each of
the lobes in your sheep’s left cortex? If you can, draw them on your sketch. How did you decide
where to put them? If not, explain why you couldn’t identify the boundaries.
Lay your brain with the bottom side up. Then compare it with the photograph of the
underside of the sheep’s brain in the Sheep Brain Dissection Guide.
Take a minute and sketch this view of your sheep brain in the space below.
Can you see any of the cranial nerves? If so, label the cranial nerves you can see on your sketch
above.
The Sensory and Motor Cortices
We have discussed how sensory information travels up from the periphery and how motor
responses travel down to the periphery. In your homework, you saw how that information is
organized in the cortex in the sensory and motor homunculi. Sheep sensory and motor
information is represented in a similar way in their cortices.
Identify the central sulcus on your sheep brain, and then identify the sensory and motor
cortices. Mark them on your sketch of the right side of the sheep’s brain. Remember that
the sensory cortex is within the parietal lobe behind the central sulcus, and the motor
cortex is within the frontal lobe in front of the central sulcus.
A Sagittal Cut to Reveal the Subcortical Organization of the Hemispheres.
Although the brain has two hemispheres, the left and right cortices are neither structurally nor
functionally symmetrical. Carefully turn the brain so that the left hand side is up – note that the
pattern of gyri and sulci are not the same as the right side. The structural differences are reflected
in functional asymmetries between the two hemispheres. We can’t detect these function
differences just by looking at the brain. However, researchers have shown that in humans, the
areas associated with hearing and speaking words are located on the left hand side of the brain,
while the area associated with the emotional component of language is situated on the right side.
(We will look at how we study the regulation of language later on in this unit.)
There are a number of ways that we can cut into the brain to reveal its inner structures. Right
now we will separate the two hemispheres in half lengthwise. This is called a sagittal cut. First,
identify the cerebellum. The cerebellum is not divided into two hemispheres and you will need to
actually cut it in half. Make sure you can see the midline where you will cut.
Beginning between the left and right frontal lobes, use your scalpel to make a careful cut to
separate the two hemispheres. As you move backwards from the cortex to the cerebellum
use the midline of the cerebellum to make sure you divide the brain exactly in two. Once
you have finished cutting, open the brain like a book to reveal the subcortical structures.
Put the left side of the brain to one side. Place the right side of the brain in front of you
with the subcortical structures facing up. Then compare it with the photograph of the
sagittal cut of the sheep’s brain in the Sheep Brain Dissection Guide.
Take a minute and sketch this view of your sheep brain in the space below.
Make sure you can identify each part visible within this cut of the brain. Next explain what each
area does in the table below, and label each area on your sketch above.
Brain Region
8. Corpus callosum
9. Thalamus
10. Hypothalamus
11. Cerebellum
12. Midbrain
13. Pons
14. Medulla
15. Spinal Cord
What does it do?
Both sensory and motor neurons cross from one side of the body to the other as they ascend and
descend respectively. In fact both sensory and motor neurons cross from one side to the other in
the medulla.
Therefore, if you damage your sensory neurons above the medulla, will you lose sensation on the
same side of your body as the damage or on the opposite side?
What about if you damage your sensory neurons below the medulla, will you lose sensation on
the same side of your body as the damage or on the opposite side?
A Coronal Cut to Reveal the Grey and White Matter of the Hemispheres.
Take your scalpel and in the frontal lobe, make a careful coronal cut to reveal the grey and
white matter of the cortex. Once you have finished cutting, examine the interior of the
cortex and compare it to the picture of a coronal section in the Sheep’s Brain Dissection
Guide.
Take a minute and sketch this view of your sheep brain in the space below.
The grey matter contains the neuron’s cell bodies, and the white matter contains the myelinated
axons traveling to and from the cortex. Label the grey and white matter in your sketch above.