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Autonomic nervous system (ANS)
The nerves, which make up the autonomic nervous system, are colored purple. The cranial nerves are not visible in this diagram
Autonomic Nervous System (ANS)
The ANS controls and coordinates the body’s ‘automatic’ functions and thus is involuntary. These automatic functions are heartbeat, digestion, excetion and , to an extent, breathing.
There are two major subdivisions that have opposite effects:
· the sympathetic ANS
· the parasympathetic ANS.
Usually, the two divisions have opposing actions and operate in a highly coordinated manner.
The sympathetic ANS prepares the body for action while the parasympathetic ANS calms it.
One familiar example is seen in heart rate. The human heart ,without outside influence, contracts at about 70-80 times a minute. Heart reate will speed up when stimulated by a sympathetic nerve and slow down when signalled by a parasympathetic nerve. The parasympathetic ANS encourages digestive processes.
Another instance, when a man feels danger, the sympathetic ANS signals the liver to release glucose to give added energy for fight or flight action while the parasympathetic ANS depresses digestion.
The nerves that make up the parasympathetic division originate in the brain and at the lower region of the spinal cord. Some go directly to the organs ; others meet other nerves which relay the impulse.
The sympathetic neurons all originate in the gray matter of the spinal cord. The gray matter of the spinal cord is in the centre of the cord. These neurons do not meet their target organs but allow other neurons to pass on its impulse.
*A motor neuron is a nerve cell in a motor nerve. A motor nerve carries impulse from the central nervous system (eg spinal cord) to the muscle .
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