The nervous system is the major controlling,
regulatory, and communicating system in the body. It
is the center of all mental activity including thought,
learning, and memory. Together with the endocrine system,
the nervous system is responsible for regulating and
maintaining homeostasis.
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Through its receptors, the nervous system keeps us in touch
with our environment, both external and internal.
Like other systems in the body, the nervous system is composed
of organs, principally the brain, spinal cord, nerves, and
ganglia.
These, in turn, consist of various tissues, including nerve,
blood, and connective tissue. Together these carry out the
complex activities of the nervous system.
The various activities of the nervous system can be grouped
together as three general, overlapping functions:
- Sensory
- Integrative
- Motor
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Millions of sensory receptors detect
changes, called stimuli, which occur inside and outside
the body. They monitor such things as temperature, light,
and sound from the external environment. Inside the
body, the internal environment, receptors detect variations
in pressure, pH,
carbon
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dioxide concentration, and the levels of various electrolytes.
All of this gathered information is called sensory input.
Sensory input is converted into electrical signals called
nerve impulses that are transmitted to the brain. There the
signals are brought together to create sensations, to produce
thoughts, or to add to memory; Decisions are made each moment
based on the sensory input. This is integration.
Based on the sensory input and integration, the nervous system
responds by sending signals to muscles, causing them to contract,
or to glands, causing them to produce secretions. Muscles
and glands are called effectors because they cause an effect
in response to directions from the nervous system. This is
the motor
output or motor function.
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