Download The Nervous System

8
The Nervous System
After studying this chapter, you will be able to:
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Name the parts of the nervous system and discuss the function of each
part
Define the combining forms used in building words that relate to the
nervous system
Name the common diagnoses, laboratory tests, and clinical
procedures used in testing and treating disorders of the nervous
system
List and define the major pathological conditions of the nervous
system
Define surgical terms related to the nervous system
Structure and Function
The nervous system directs the function of all the human body systems
(Figure 8-1). The nervous system is divided into two subsystems: the central
nervous system (CNS) and the peripheral nervous system (PNS).
A nerve cell or neuron is the basic element of the nervous system. All
neurons have three parts:
1. The cell body, which has branches or fibers that reach out to send or
receive impulses.
2. Dendrites, which are thin branching extensions of the cell body. They
conduct nerve impulses toward the cell body.
3. The axon, which conducts nerve impulses away from the cell body. It
is generally a single branch covered by fatty tissue called the myelin
sheath, itself covered by the neurilemma. At the end of the axon, there
are terminal end fibers.
Nerve impulses jump from one neuron to the next over a space called
a synapse. The nerve impulse is stimulated to jump over the synapse by a
neurotransmitter, any of various substances in the terminal end fibers.
All neurons also have two basic properties—excitability, the ability to
respond to a stimulus (anything that arouses a response), and conductivity,
the ability to transmit a signal. Neurons are microscopic entities that form
bundles called nerves, which carry electrical messages to the organs and
muscles of the body. The three types of neurons are:
1. Efferent (motor) neurons, which convey information to the muscles
and glands from the central nervous system
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