SBU4U1
Student Names:__________________________
Chapter 8 Investigation: The Mammalian Brain
Objective: To examine the structures of the brain using the sheep brain.
Materials: safety goggles
latex gloves
lab aprons
dissecting trays
photos/diagrams
models human brain
observation and evaluation sheets
Procedure:
Part 1: External Structure
1.
Obtain a sheep brain from the teacher. The brain should be rinsed
in water to remove excess preservative.
2.
Examine the surface features from dorsal, lateral, and ventral view
identifying the 3 major structures visible.
a. The large cerebrum is composed of the two cerebral
hemispheres. They form the largest part of the forebrain.
b. The cerebellum is the highly convoluted structure behind the
cerebrum and above the brain stem. The cerebellum is part of
the hindbrain.
c. The brain stem extends from the spinal cord (the cut region)
through the base and part of the central interior of the brain.
Because the brain stem extends the length of the brain, it
includes a portion of the hindbrain, the forebrain, and all of the
midbrain.
Q1. What is the function of each of these structures :
a. cerebrum
b. cerebellum
c. brain stem
3.
Examine the cerebrum and note the convoluted appearance of its
surface. A membrane called the meninges covers the surface of
the cerebrum.
Q2. What are the 3 layers of this structure and what ailment can afflict the
meninges.
a. layer 1b. layer 2c. layer 3-
4.
Q3.
The convolutions are formed by the raised areas or ridges, called
gyri, and the depressed areas called fissures. The major fissures
divide the important lobes of the cerebrum. Examine the human
brain models and the sheep brain. Note differences in crenulations
and in fissures.
Describe differences between surface of sheep and human cerebra.
Q4. What are the four lobes of the human brain; what is their function.
Lobe
5.
Function
a.
-
b.
-
c.
-
d.
-
Locate the highly convoluted cerebellum, which is posterior to the
cerebral hemispheres. Compare the cerebellum of the sheep brain
to the model or diagram of the human brain. Note that the human
and sheep brains are different medially and longitudinally.
Q6. What is this difference?
6. Examine the ventral surface of the sheep brain and locate the
medulla oblongata, which begins where the spinal cord widens, just
below the cerebellum. The medulla oblongata contains regions where
motor nerves from the right side of the cerebrum cross over to the left
side of the spinal cord , and vice versa. Some sensory nerves
traveling to the brain also cross over in the medulla, and others cross
over where the nerve enters the spinal cord.
Q7. What is the purpose of the medulla oblongata?
6.
On the ventral surface, moving forward from the spinal cord, note
that just in front of the medulla oblongata is a rounded structure
called the pons.
Q8. What is the purpose of the pons?
7.
The optic chiasma forms an “X” on the ventral surface of the brain.
Q9. What is the function of the chiasma?
Part 2: Internal Structure. Use the Half Brain for the following.
8.
Observe the internal view of the sheep brain that has been
dissected in the sagital plane and locate the following structures
that were seen in the dorsal and ventral views of the whole brain:
cerebrum, cerebellum, medulla oblongata, spinal cord, and optic
chiasma. Note also the corpus callosum.
Q10. What is the purpose of the corpus callosum?
9.
Note the difference in colour of the outer and inner regions of the
cerebellum. Note this too in the cerebrum.
Q11. Explain the differences in colour.
DIAGRAMS
VENTRAL DIAGRAM:
DORSAL DIAGRAM:
SAGITTAL DIAGRAM: