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Biology 12: Brain Lab
INTRODUCTION: The brain is the master organ of our body and the nervous system is the
network of nerves through which the brain receives and sends out nerve impulses. The brain is
well protected by a number of membranes, as well as fluid, bone, and skin. There are three
membranes that surround the brain; the pia mater is the membrane next to the brain and it is richly
supplied with blood vessels, the middle membrane is the arachnoid mater, while the outermost
membrane is the dura mater. Located between the arachnoid mater and the pia mater is the
cerebrospinal fluid, which provides a cushioning effect for the brain. The three membranes are
known collectively as the meninges. Further protection for the brain is provided by the bony
cranium.
The spinal cord, also part of our central nervous system (CNS), extends from the base of the
brain down through the vertebrae. Peripheral nerves, composed of many neurons, attach directly
to the brain or to the spinal chord. Cranial nerves are those that extend from the brain, while
spinal nerves extend from the spinal chord. Nerves can be further subdivided according to the
type of message they carry. Sensory (afferent) nerves carry messages to the CNS, while motor
(efferent) nerves carry messages to the organs of the body. Occasionally, some nerves carry both
sensory and motor neurons, and are known as mixed nerves.
PURPOSE: To study the external and internal structure of a mammalian brain.
APPARATUS AND MATERIALS:
 sheep brain
 dissecting tray

forceps

probe
PROCEDURE:
1. AFTER READING THE INTRODUCTION, obtain 2 halves of a sheep brain and make
observations of it's external features (e.g. size, colour, texture, appearance). Identify the
cerebrum, cerebellum, medulla oblongata, and pons. Note the convolutions of the two
cerebral hemispheres. The convolutions are composed of crests called gyri and fissures or dips
called sulci.
2. Observe the dorsal surface of the brain and note the longitudinal fissure which separates the
cerebral hemispheres.
3. Locate the cerebellum. Describe its structure. What is its function?
4. Locate the medulla oblongata (this is the part of the brain that is continuous with the top of the
spinal cord).
5. Examine the ventral surface of the brain. Locate the pons and note the stumps of a number of
cranial nerves which attach to the pons and the medulla (these may be very short or missing).
6. Move posteriorly along the longitudinal fissure until a white, X-shaped structure is seen. This
is called the optic chiasma. It is the remnant of nerves coming from each eye.
7. Posterior to the optic chiasma is the pituitary gland. See if it is still attached to your sheep's
brain. If the gland is still attached to the brain, there is a short stalk called the infundibulum by
which the gland is suspended from the brain. The stalk is itself attached to the hypothalamus.
What are the functions of the hypothalamus?
8. Look at the inner surface of one half of your brain. Note the corpus callosum, which is the
large, white commissure which is located between the cerebral hemispheres. What is its
function? Notice the colour of the cerebral cortex in comparison to the colour of the corpus
callosum.
9. Try to located the thalamus. The thalamus is a nerve center located just beneath the round
commissure which is the region just posterior and ventral to the corpus callosum. This round
commissure connects the right and left thalamic areas of the brain.
10. Observe the medulla oblongata. What are the functions of the medulla oblongata?
QUESTIONS:
1. There are a number of structures and substances that protects the brain from injury. Name
these.
2. How is the surface area of the cerebrum increased without an increase in the total volume of
the brain?
For marks, hand in on a sheet of paper:
1) Your organized, detailed observations done while doing the lab,
written in complete sentences.
2) Your answers to the above questions in complete sentences.
Bonus:
Use the dissecting microscope to observe a cross section of a spinal cord.
Make a detailed diagram and label as much as possible. Your sketch
should be at least 1/3-1/2 a page in size. Attach this to your assignment.