parasympathetic 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.

parasympathetic nervous system

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.
Figure 1: Efferent nerve pathways from the brainstem and spinal cord. Shown on the right: somatic, to skeletal muscles. Shown on the left: autonomic. B brain stem, C cervical, T thoracic, L lumbar, S sacral segments of the spinal cord. (Red shaded regions are those with no autonomic outflow.)
Figure 2: The autonomic nervous system. Actions on the heart and on smooth muscle. Sympathetic actions on the left and parasympathetic actions on the right. Solid arrows: stimulation (contraction or secretion); broken arrows: inhibition.

parasympathetic nervous system

one of the two components of the autonomic nervous system. Preganglionic nerve fibres come from the brain stem and from the sacral segments of the spinal cord ('craniosacral outflow'), i.e. from the central nervous system above and below the sympathetic outflow. These nerves relay in ganglia close to the organs where they act (including heart, lungs, gastrointestinal tract). Most of the cranial components travel in the vagus nerves. In general, parasympathetic nerves stimulate the functions of the alimentary and genitourinary systems, whereas effects on the cardiorespiratory system are appropriate to relative inactivity, e.g. slowing the heart rate. See also acetylcholine, atropine, sympathetic nervous system; Figure 1, Figure 2.

parasympathetic nervous system

; parasympathetic (craniocaudal) division of the autonomic nervous system cell bodies of motor nerves located within the medulla oblongata and intermediate columns of spinal cord (i.e. at cranial nerves III, VII, IX and X and S2-S4 levels); preganglionic parasympathetic synapses use acetylcholine as neurotransmitter; postganglionic fibres use adrenaline as neurotransmitter

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.

parasympathetic

pertaining to the parasympathetic nervous system.

parasympathetic cholinergic vasodilator fibers
cause dilatation of blood vessels in tissues including cerebral vessels, tongue, salivary glands, external genitalia, bladder, rectum.
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 several sacral nerves (depending on species); postganglionic fibers are distributed to the heart, smooth muscles, and glands of the head and neck, and thoracic, abdominal and pelvic viscera. Almost three-quarters of all parasympathetic nerve fibers are in the vagus nerves, which serve both the thoracic and abdominal regions of the body.
The predominant secretion of the nerve endings of the parasympathetic nervous system is acetylcholine, which acts on the various 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. Excitation of the sympathetic nervous system often results in an effect opposite to that of the parasympathetic system; however, most organs are predominantly under the control of either one or the other of the two nervous systems that compose the autonomic nervous system.
parasympathetic outflow
the total of parasympathetic nerves which leave the central nervous system. Includes the cranial and sacral outflows.
References in periodicals archive ?
The rapid focal firing within or near LSPV as well as abnormal conduction between LA and PV and within PV under abnormal parasympathetic tone was happy to produce AF.
7) The reverse is true with an increase of parasympathetic tone.
sup][10] In patients with severe ischemic stroke, autonomic dysfunction particularly depresses the parasympathetic tone.
Previous studies have shown that RMSSD primarily reflect the parasympathetic tone [15,16] and SDNN is considered to reflect both the sympathetic and the parasympathetic influence on heart rate variability.
This suggests an increase in parasympathetic tone to the heart.
If sympathetic tone is overbearing parasympathetic tone, that needs to be corrected to reduce cardiovascular risk.
In contrast, authors of a recent field study reported a decrease in respiratory sinus arrhythmia associated with indoor traffic noise exposure during sleep, consistent with an effect mediated by a reduction in parasympathetic tone (Graham et al.
15 Hz: LFP) is thought to be generated by baroreceptor modulation of sympathetic and parasympathetic tone (18,20).
These drugs can cause functional and behavioural disorders by permanently altering the balance of sympathetic and parasympathetic tone in the individual.
It has been reported that ST elevation and ventricular arrhythmogenicity are augmented by the parasympathetic tone in BS (7).
During the day sympathetic tone predominates causing an increase in resting heart rate on waking; exercise causes an immediate further increase in heart rate because of an abrupt reduction in parasympathetic tone and sympathetic activation, so [beta]-blockade reduces heart rate.
41,43-46] Physical activity enhances the parasympathetic tone, and a reduced heart rate (induced by vagal influence) is considered as an index of training status in athletes.

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