g. Rectum and Anus. The rectum, continuous with the large intestine, is about
6 inches in length. It receives feces from the large intestine and periodically expels it
through the anus. The anus is the external opening at the end of the digestive tract.
1-11. NERVOUS SYSTEM
This system includes a group of organs which controls and integrates the
intellectual and physical processes of the individual. The nervous system is made up of
nerve tissues. The main structure of the conductive nerve tissues is the neuron, a
specialized cell designed to conduct electrical impulses. The nervous system is divided
into the central nervous system, the peripheral nervous system, and the autonomic
nervous system.
a. Central Nervous System. The central nervous system includes the brain
and the spinal cord (see figure 1-13). The brain, located within the cranium, is the
control center of the body. Within the brain, specific areas control specific body
functions. For example, there are control centers for speech, sight, hearing, movement,
heartbeat, breathing rate, and body temperature. The spinal cord is a reflex control
center. It is composed of countless nerve fibers. These nerve fibers go down from and
go up to the brain. The spinal cord is enclosed in the spinal column (backbone) for
protection. The nerves of the peripheral and autonomic nervous systems have their
roots in the central nervous system,
Figure 1-13. Central nervous system.
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