Functional overview o f th e nervo u s sy stem • Figure 7.2
walls of the digestive organs and the sensory organs. Not
to be confused with neurons, nerves are bundles of nerve
fibers in the peripheral nervous system. The PNS is subdi-
vided further according to functions of groups of sensory
and motor neurons ( •
The afferent (sensory) nervous system consists of
a variety of nerve receptors and their associated nerve
fibers:
Som atosensory receptors
are associated with the muscles,
joints, and skin.
S p ec ia l sense receptors
are found in the ear, eye, nose,
and tongue.
A u to n o m ic sensory receptors
are found in the internal
organs.
The efferent (motor) nervous system is composed
of motor nerve fibers that regulate the activities of
muscle and glandular tissues throughout the body.
This system can be subdivided into three sections:
• The somatic nervous system (SNS) deals with
initiating
voluntary
(under
conscious
control)
skeletal muscle actions that move the body around
in space.
• The autonomic nervous system (ANS) regulates
involuntary functions (such as heart rate, breathing
rate,
and
body
temperature)
involving
cardiac
muscle, smooth muscle, and glandular tissue. This
system consists of two divisions, sympathetic and
parasympathetic, which have opposite effects.
• The enteric nervous system (ENS) is an intricate
network of nerve fibers within the digestive organs
that
regulates
the
involuntary functions
of the
digestive system and interacts with the ANS.
Like a computer, your nervous system accomplishes
the following functions:
1.
Sensory fu n c tio n
(inform ation
in p u t).
Neurons
in
the
peripheral nervous system
(PNS)
sense changes in
internal and external environments, such as changes in
blood pressure, injuries, touch, and pain, and send this
information to the central nervous system (CNS).
2.
In teg ra tiv e fu n c tio n (in fo rm a tionprocessing).
Neurons in the
CNS analyze sensory information and make decisions
unconsciously
or
consciously.
Conscious
decisions
require perception (or mental awareness) and higher-
level processing.
3.
M o to r fu n c tio n
(inform ation
o u tp u t).
After
processing
information and making decisions, CNS neurons send
commands to muscular or glandular effectors that carry
out responses such as muscle contraction/relaxation or
increased/decreased secretion of substances such as oil
or sweat.
Let’s take a closer look at the cells that make up the
nervous system.
Nerve Cells "Talk" to Each Other 193
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