Sheep´s brain dissection guide. 2011-12 Biology - level 3º ESO. biodeluna.wordpress.com Zaragoza - Spain

1. Sheep´s brain dissection
First examine the exterior of the entire brain. The meninges are the protective coverings, which
enclose the brain and spinal cord.You may be able to see one or two of the three layers of the
meninges, the dura mater, the arachnoid layer, and the pia mater.
Next locate the area referred to as the brain stem (medulla + pons + midbrain). Find also the root
where the pituitary gland or hypophysis was (or if youa are lucky it is still) attached to your brain.
Find the medulla (oblongata) which is an elongation below the pons. The medulla is located
right under the cerebellum. In this the nerves cross over so the left hemisphere controls the right
side of the body and vice versa. This area of the brain controls the vital functions like heartbeat
and respiration (breathing).
The pons is next to the medulla. It serves as a bridge between the medulla and the upper
brainstem, and it relays messages between the cerebrum and the cerebellum.
The pituitary gland or hypophysis, which produces important hormones, is a pea size sac-like
area that attaches to the brain between the pons and the optic chiasm. This may or may not be
present on your
specimen.
Examine the ventral surface of the sheep brain where you can find a pair of olfactory bulbs, one
under each lobe of the frontal cortex. Several important parts of the visual system are visible in the
ventral view of the brain. Muscles, other nerves and fatty tissue may surround the optic nerve on
your specimen. After inspection of these, use a scalpel to cut away this muscle tissue, leaving as
much of the optic nerve as possible protruding from the ventral side of the brain. Notice that as
the optic nerves from the right and left eyes proceed towards the center of the brain, they meet in
the optic chiasm (named for the Greek letter chi, C, which it resembles). In the optic chiasm,
there is a partial crossover of fibers carrying visual information. Any time fibers in a tract or nerve
cross the midline of the brain it is called a decussation.

2. The cerebrum is divided into approximately symmetric hemispheres.
The corpus callosum is a bundle of white fibers that connects the two hemispheres of the brain,
providing coordination between the two.
Now find the four lobes of the cerebrum: frontal, parietal, temporal, and occipital.
Examination of the Mid-Saggital Cut.
Use a scalpel (or sharp, thin knife) to slice through the brain along the center line, starting at the
cerebrum and going down through the cerebellum, spinal cord, medulla, and pons.
Now you can see the cerebellum. To some it resembles a tree or bush and is called as a result
the arbor vitae (the tree of life).
Look closely at the inside of the cerebellum to notice the pattern of grey and white matter. You
should see a branching "tree" of lighter tissue surrounded by darker tissue. The branches are
white matter, which is made up of nerve axons. The darker tissue is gray matter, which is a
collection of nerve cell bodies. You can see gray and white matter in the cerebrum, too, if you cut
into a portion of it.
This dissection guide was elaborated thanks to the resources from:
 http://psych.hanover.edu/classes/neuropsychology/Syllabus/Labs/DISSECTION.pdf
 http://www.hometrainingtools.com/brain-dissection-project/a/1316/
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