parasympathetic nervous system

(redirected from parasympathetic craniocaudal division of the autonomic nervous system)
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parasympathetic nervous system

 
part of the autonomic nervous system, the preganglionic fibers of which leave the central nervous system with cranial nerves III, VII, IX, and X and the first three sacral nerves; postganglionic fibers are distributed to the heart, smooth muscles, and glands of the head and neck, and thoracic, abdominal, and pelvic viscera. (See also Color Plates.) Almost three-fourths of all parasympathetic nerve fibers are in the vagus nerves, which serve the entire thoracic and abdominal regions of the body.

The predominant secretion of the nerve endings of the parasympathetic nervous system is acetylcholine, which acts on organs of the body to either excite or inhibit certain activities. For example, stimulation of the parasympathetic system causes constriction of the pupil of the eye and contraction of the ciliary muscle; increase of the glandular secretion of enzymes, as in the case of the pancreas; increased peristalsis; and a slowed heart rate. It often happens that excitation of the sympathetic nervous system results in an effect opposite that of the parasympathetic system; however, most organs are under the almost exclusive control of either one or the otherof the two nervous systems that compose the autonomic nervous system.

parasympathetic nervous system

n.
The part of the autonomic nervous system originating in the brainstem and the lower part of the spinal cord that, in general, inhibits or opposes the physiological effects of the sympathetic nervous system, as in tending to stimulate digestive secretions, slow the heart, constrict the pupils, and dilate blood vessels.

par·a·sym·pa·thet·ic ner·vous sys·tem

(par'ă-sim'pă-thet'ik nĕr'vŭs sis'tĕm)
The branch of the autonomic nervous system that sends motor signals to glandular smooth muscle, and cardiac tissue, during recovery from threat.
Compare: sympathetic nervous system

parasympathetic nervous system

One of the two divisions of the AUTONOMIC NERVOUS SYSTEM. The parasympathetic system leaves the central nervous system in the 3rd, 7th, 9th and 10th CRANIAL NERVES and from the 2nd to the 4th SACRAL segments of the spinal cord. Parasympathetic action constricts the pupils of the eyes, promotes salivation and tearing, slows the heart, constricts the BRONCHI, increases the activity of the intestines, contracts the bladder wall and relaxes the SPHINCTERS and promotes erection of the penis. See also SYMPATHETIC NERVOUS SYSTEM.

Parasympathetic nervous system

The division of the autonomic (involuntary or unwilled) nervous system that slows heart rate, increases digestive and gland activity, and relaxes the sphincter muscles that close off body organs.

par·a·sym·pa·thet·ic ner·vous sys·tem

(par'ă-sim'pă-thet'ik nĕr'vŭs sis'tĕm)
Branch of the autonomic nervous system that sends motor signals to glandular smooth muscle, and cardiac tissue, during recovery from threat.