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give an example of external stimuli
The human nervous system is a control system, which regulates the body’s responses to internal and external stimuli.
Page 2 The Neuron
See Graphic of a Typical Neuron - (Figure 12-1)
A neuron is the nerve cell body plus all of its processes and coverings.
The neuron (nerve cell) is the conducting unit of the nervous system. It is
specialized to be irritable and transmit signals, or impulses. The neurons are held
together and supported by another nervous tissue known as neuroglia, or simply glia.
Page 3 Elements of the Human Nervous System
A nerve is a collection of neuron processes together and outside of the CNS.
A fiber tract is a collection of neuron processes together and within the CNS.
A ganglion is a collection of nerve cell bodies together and outside of the CNS.
A nucleus is a collection of nerve cell bodies together and within the CNS.
Page 4 General Versus Special
If a nervous element is found throughout the body, it is said to be general.
A nervous element located in just one part of the body, such as the head, is said to be special.
For example, there are general senses, such as pain and temperature, and there are special sense
organs, such as the eyes and the ears.
Page 5 Somatic Versus Visceral
The term somatic refers to the peripheral part of the body. Thus, when we speak of somatic innervation,
we are talking about the nerve supply to the trunk wall, upper and lower members, head, and neck.
SOMA = body, body wall
The term visceral refers to the visceral organs.
These include hollow organs with smooth muscle (such as the intestines and the blood vessels) as well as
Thus, visceral innervation refers to the nerve supply for these organs.
Note that the visceral organs are located within both the trunk and periphery of the body.
Those in the periphery include the blood vessels and the sweat glands.
Page 6 Synapses
The human nervous system is an integrated, connected circuitry of nervous tissues.
It is supplied with special junctions called synapses.
The synapses ensure the flow of information along the circuitry in the proper direction.
In general terms, the human nervous system can be compared to a computer.
There is input--the sensory information.
There is central collation of input along with previously stored information.
COLLATE = collect, compare, and arrange in order
Once a decision has been reached by the central portion, there is an output of commands to the effector organs (muscles and/or glands).
Page 8 Speed of the Nervous System
There are various control systems to be found within the body.
Of these, the nervous system is the most rapid and precise in responding to specific situations.
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