parasympathetic nervous system

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parasympathetic nervous system:

see nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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Parasympathetic nervous system

A portion of the autonomic system. It consists of two neuron chains, but differs from the sympathetic nervous system in that the first neuron has a long axon and synapses with the second neuron near or in the organ innervated. In general, its action is in opposition to that of the sympathetic nervous system, which is the other part of the autonomic system. It cannot be said that one system, the sympathetic, always has a excitatory role and the other, the parasympathetic, an inhibitory role; the situation depends on the organ in question. However, it may be said that the sympathetic system, by altering the level at which various organs function, enables the body to rise to emergency demands encountered in flight, combat, pursuit, and pain. The parasympathetic system appears to be in control during such pleasant periods as digestion and rest. The alkaloid pilocarpine excites parasympathetic activity while atropine inhibits it. See Autonomic nervous system, Sympathetic nervous system

Parasympathetic Nervous System

 

the part of the autonomic nervous system whose ganglia are located very close to or in the innervated organs. The centers of the parasympathetic nervous system are found in the mesencephalon and medulla oblongata and in the sacral part of the spinal cord. The fibers of the parasympathetic nervous system proceed to the viscera as part of the third (oculomotor), seventh (facial), ninth (glossopharyngeal), and especially the tenth (vagus) cranial nerves and as part of the pelvic nerve.

In many cases, the parasympathetic and sympathetic nervous systems are directly opposed to one another in their effect on organs. Whereas sympathetic stimulation will act to accelerate and intensify heart contractions, raise the blood pressure, and dilate the pupils, parasympathetic stimulation will act to slow and weaken the heartbeat, lower arterial pressure, and contract the pupils. Efferent neurons of the parasympathetic nervous system are typically situated in the innervated organ proper and not in the separate trunk, as is the case in the sympathetic nervous system. The mediator substance formed in the nerve endings of the parasympathetic nervous system is acetylcholine; the predominant mediator substance in the sympathetic nervous system is norepinephrine.

O. M. BENIUMOV

parasympathetic nervous system

[¦par·ə‚sim·pə′thed·ik ′nər·vəs ‚sis·təm]
(neuroscience)
The craniosacral portion of the autonomic nervous system, consisting of preganglionic nerve fibers in certain sacral and cranial nerves, outlying ganglia, and postganglionic fibers.
References in periodicals archive ?
During morning training session E-types had significant higher vagal indices with a significant lower parasympathetic tone that returned to the rest values after 24 hours the cessation of HIIT.
However, this does not imply that there is no specific physiological effect of acupuncture treatment as we found an acupuncture-specific increased parasympathetic tone accompanied by an increase of pain-related QoL.
The burst pacing with higher AF inducibility than premature beat indicated that in addition to the parasympathetic tone, the rapid focal firing within LSPV was another condition for AF inducement.
Exercise elevates the parasympathetic tone to the [atrioventricular] node and so decreases the ventricular rate," she said.
These physiologic changes were paralleled by feelings of well-being and mental brightness, which might be attributed to the enhancement of neural sympathetic activity, as revealed by the rise of the NA but not Ad plasma levels, together with the increase of parasympathetic tone, as revealed by the neurophysiologic, neurochemical, and clinical parameters.
One hypothesis is that omega-3 fatty acids have some effects on the autonomic nervous system--in particular, by increasing parasympathetic tone.
Eating may decrease symptoms by increasing parasympathetic tone.
It has been shown that HRV depends on the relationship of the sympathetic and parasympathetic tone.
The pupil has an exclusively autonomic innervation, pupil diameter reflecting the balance between sympathetic and parasympathetic tone, thus constituting a sensitive test system of central and peripheral autonomic activity.
The CardioFit system increases the parasympathetic tone by applying electrical impulses to the vagus nerve.
The assumption of the standing position after supine rest for 30 min results in venous pooling of blood and a transient decrease in cardiac output eliciting reflex activation of the sympathetic nervous system and a withdrawal of cardiac parasympathetic tone.

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