Dictionary > Parasympathetic nervous system

Parasympathetic nervous system

Definition
noun
A division of the (vertebrate) autonomic nervous system whose physiological effects are mostly in opposition to those of the sympathetic nervous system; e.g. it is involved in the slowing of the heart beat and relaxing the muscles.
Supplement
The parasympathetic neurons lie between the brain and the spinal cord. Most of them have cholinergic nerve endings (i.e. involving acetylcholine as neurotransmitter) and their responses are mediated by muscarinic receptors. They are known to produce responses that inhibit or oppose the actions of the sympathetic nervous system. Whereas the sympathetic nervous system is responsible for the fight-or-flight responses the parasympathetic nervous system is mainly involved in responses or effects found during rest, sleep and digestion. The system innervates the salivary glands, thoracic and abdominal viscera, bladder and genitalia where the physiological effects produced are involuntary, such as stimulating digestive secretions, slowing heart rate, constricting the pupils, dilating the blood vessels, etc.
Compare: sympathetic nervous system
See also: autonomic nervous system


You will also like...

Early Mammals on Earth
Early Mammals on Earth

The Earth's ecosphere was rapidly changing and throwing up a wide range of ecological niches that new adaptive organisms..

Electromagnetic spectrum of a brain
Sleep and Dreams – Neurology

While learning and intelligence are associated with the functions of a conscious mind, sleep and dreams are activities o..

Digestion and Absorption of Food
Digestion and Absorption of Food

The gastrointestinal system breaks down particles of ingested food into molecular forms by enzymes through digestion and..

Homeostatic Mechanisms and Cellular Communication
Homeostatic Mechanisms and Cellular Communication

Homeostasis is the relatively stable conditions of the internal environment that result from compensatory regulatory res..

Disturbance on a still water
Abiotic Factors – Water Conditions

A still body of water may be disturbed by a variety of factors. One of them is wind. In fact, it is considered as the pr..

river
Running Water Freshwater Communities

This tutorial introduces flowing water communities, which bring new and dithering factors into the equation for possible..