2.  Thecentral nervous system includes the
brain and the spinal cord. We will learn
about a lot of structures that are part of
the brain and spinal cord in this section.

3.  Theperipheral nervous system is the part of
the nervous system that is outside of the
brain and spinal cord. It is divided into two
parts: the somatic nervous system and the
autonomic nervous system. The somatic
nervous system is responsible for conveying
messages from the sense organs to the
central nervous system and from the central
nervous system to the muscles. The
autonomic nervous system controls the
heart, the intestines, and other body organs.

4.  The spinal cord is the part of the central
nervous system that is in the spinal column
and communicates with the sense organs and
muscles below the head. The spinal cord is
made up of segments, and each segment has
particular components. These include a
bundle of axons that carry sensory
information to the spinal cord and a cluster
of neurons that carry information to the
muscles. There are two sensory axons and
two clusters of motor neurons on each side
of each segment of the spinal cord. Each
segment of the spinal cord sends sensory
information to the brain and receives motor
commands from the brain

5.  Thespinal cord is made up of two kinds of
matter: gray matter and white matter.
The gray matter is in the center of each
segment of the spinal cord and has a lot
of cell bodies and dendrites. The white
matter is toward the outside of each
segment of the spinal cord and is made up
of myelinated axons.

6.  Ifthe spinal cord is
cut, then the brain
loses its ability to
feel from that
segment of the
spinal cord where
the cut occurred
and all the
segments below it,
and the brain loses
motor control over
all parts of the body
served by that A single segment of the spinal

cord with the gray matter,
segment of the white matter, motor nerve and
spinal cord and all sensory nerve indicated.
segments below it.

7.  Theautonomic nervous system is made up
of neurons that receive information from
the heart, intestines, and other organs
and send commands to these organs. The
autonomic nervous system is composed of
two parts: the sympathetic nervous
system and the parasympathetic nervous
system.

8.  Thesympathetic nervous system prepares
the body for activity and causes your body’s
organs to rev up for the action. For
example, if you had to try and catch a
baseball or run in a race, the sympathetic
nervous system would prepare your body for
these activities. The parasympathetic
nervous system prepares the body for rest
and relaxation. After a hard day at school, if
you are just sitting around watching TV, your
parasympathetic nervous system is causing
your body’s organs to relax.

9. Autonomic nervous system showing the sympathetic nervous system (left) and

the parasympathetic nervous system (right).