Download Nervous System

NERVOUS SYSTEM READING
The nervous system of many animals consists of the brain, the spinal cord, and nerves. This system
allows animals to obtain quick feedback about their surroundings and to react immediately. The nervous
system can be separated into two divisions, the central nervous system which includes the brain and spinal
cord and the peripheral nervous system which includes all of the nerves that branch off to various parts of
the body.
Complete questions 1-4 on the worksheet.
Be extremely careful during this portion
of the dissection as the brain tissue is
very fragile. You will examine the brain
and the spinal cord that is connected at
the posterior end of the brain. To do this,
CAREFULLY cut into the cranium
between the eyes. Cut about the cranium
in pieces (if need be) being very careful
not to cut too deep. Keep removing
pieces of skull until you have cut past
each ear to the back of the head or top of
the neck.
http://www.k-state.edu/organismic/rat_dissection.htm
April 23, 2008
Identify the parts of the rat’s brain: olfactory bulbs, cerebral cortex, and cerebellum. The rat brain is
different from the human brain in several ways. First, the human brain has many folds called gyri; the
rat’s brain is smooth in appearance. Second, the olfactory bulbs (for smelling) of the rat brain are
proportionately much larger than in the human brain. Third, the cerebral cortex (where higher level
thinking takes place) and the corpus callosum (where the left and right halves of the brain connect to
exchange information) are proportionately much smaller in the rat’s brain than in the human. The
cerebellum (where balance and coordination are controlled) and the brain stem (where all of the
necessary vital functions are controlled) are proportionately
similar in the human and rat.
Complete questions 5-7 on the worksheet.
Continue removing the rest of the cranium until you come to
the location where the spinal cord descends into the cervical
(neck) vertebrae. Working down the vertebrae, remove the
muscle tissue until you have at least 5 or 6 vertebrae that are
revealed. Look for the intervertebral disks that act as shock
absorbers for the spine. Then look for the smaller peripheral
nerves that are exiting (or entering) the spinal cord.
With a sharp scalpel, try to carefully break through the vertebrae to reveal the spinal cord inside OR
make a cut in the spinal cord after the 6th vertebrae and try sliding the vertebrae off of the spinal cord
one by one. Identify the peripheral nerves that must be cut as you go.
http://idiolect.org.uk/notes/?cat=5&paged=2
After exposing part of the spinal cord,
carefully remove the top of the spinal
cord and brain together. Examine the
end of the spinal cord. Make a clean cut
through it if need be. You should notice
2 different areas within the spinal cord.
This is the grey matter and the white
matter of the spinal cord. The white
matter, towards the outside of the spinal
cord, is the nerve fibers that are sending
messages to and from the brain.
http://www.infovisual.info/03/024_en.html
The grey matter, inside the white matter, is the cells that support
the nerve fibers, making sure that the cells of the white matter
receive the energy that they need to function properly. The
human spinal cord is very similar to this. The brain, however, is
reversed. The grey matter is on the outside and the white matter
is on the inside.
http://www.brainexplorer.org/glossary/grey_matter.shtml
Complete questions 8-10 on the worksheet.
The cells of the nervous system are called neurons. Neurons carry messages to and from the brain by
electrical charges that run the length of the neuron and by chemicals that trigger the next neuron or
suppress the next neuron from firing. Obtain a prepared slide of neurons. A typical neuron looks
something like the drawing below, but there are other neuron types.
Sources: http://www.epilepsyfoundation.org/about/science/functions.cfm
http://lpmpjogja.diknas.go.id/kc/b/brain/brain.htm
April 25, 2008
Neurons can be classified into three types depending on direction of
the impulse. Sensory neurons send an impulse from the sense
organs to the spinal cord and brain. Motor neurons send an
impulse from the brain and spinal cord to muscles or glands.
Interneurons interconnect sensory and motor neurons.
The largest part of a typical neuron is the cell body. The cell body contains the nucleus and much of the
cytoplasm. Most of the metabolic activity of the neuron takes place in the cell body. Spreading out from
the cell body are short, branched extensions called dendrites. Dendrites carry impulses from the
environment or other neurons to the cell body. The long fiber that carries impulses away from the cell body
is called the axon. The axon ends in a series of swellings called axon terminals. The axon terminals are
where neurons link with other cells. In most animals, axons and dendrites are bundled in fibers called
nerves.
In some neurons, the axon is insulated by a membrane called the myelin sheath. The myelin sheath leaves
many gaps, called nodes, where the axon is exposed. As an impulse travels along the axon, it leaps from
node to node, speeding up the impulse.
Complete questions 11-13 on the worksheet.
The synapse is the location
where an impulse is transferred
to another neuron. The axon
terminal of the first neuron fits
very closely with the dendrite
on the second neuron, leaving a
very small gap. The axon
terminal contains tiny vesicles
filled with chemicals called
neurotransmitters. The
vesicles move to the edge of
the axon terminal and release
their neurotransmitters into the
gap by the process of
exocytosis. The
neurotransmitters cross the gap
by the process of diffusion.
Receptors on the dendrite
across the gap receive the
neurotransmitters.
Complete question 14 on the worksheet.
http://www.coolschool.ca/lor/BI12/unit12/U12L04.htm