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Encyclopedia > Parasympathetic nervous system
Autonomic nervous system innervation, showing the sympathetic and parasympathetic (craniosacral) systems, in red and blue, respectively

The parasympathetic nervous system is one of three divisions of the autonomic nervous system. Sometimes called the rest and digest system, the parasympathetic system conserves energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract. Image File history File links Download high resolution version (479x700, 74 KB)Sympathetic (red) and parasympathetic (blue) nervous system, from Grays Anatomy 1918 (public domain), at http://www. ... Image File history File links Download high resolution version (479x700, 74 KB)Sympathetic (red) and parasympathetic (blue) nervous system, from Grays Anatomy 1918 (public domain), at http://www. ... This article or section is in need of attention from an expert on the subject. ... Look up Sphincter in Wiktionary, the free dictionary. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and...

Contents

Relationship to sympathetic nervous system

Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better termed complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. Grays FIG. 838– The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses. ...


Physical Location

The parasympathetic nervous system is a portion of the visceral (autonomic) branch of the PNS (peripheral nervous system). The regions of the body associated with this division are the cranial and sacral regions of the spinal cord. Specifically, cranial nerves III, VII, IX, X (vagus n.) and in the sacral region (spinal nerves exiting from the sacrum) the spinal nerves S2 to S4.


Similar to the sympathetic division, the parasympathetic division also has pre- and post- ganglionic neurons. Typically, in the parasympathetic division the ganglion will be closer to the area of innervation - unlike the sympathetic ganglion which form immediately lateral and inferior to the spinal nerve - making up the so called "chain ganglion".


Receptors

The parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter. The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors. Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of the postganglionic nerve. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ. The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... Muscarinic receptors are those membrane bound acetylcholine receptors that are more sensitive to muscarine than to nicotine. ... Nicotinic Receptors form ion channels present in the plasma membrane of cells. ... A synapse is cholinergic if it uses acetylcholine as its neurotransmitter. ... In the autonomic nervous system, fibers from the CNS to the ganglion are known as preganglionic fibers. ... In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers. ...


Types of muscarinic receptors

The three main types of muscarinic receptors that are well characterised are:

  • The M1 muscarinic receptors (CHRM1) are located in the neural system.
  • The M2 muscarinic receptors (CHRM2) are located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the sinoatrial node (SA node) and atrioventricular node (AV node). Note, they have no effect on the contractile forces of the ventricular muscle.
  • The M3 muscarinic receptors (CHRM3) are located at many places in the body, such as the smooth muscles of the blood vessels, as well as the lungs, which means that they cause vasoconstriction and bronchoconstriction. They are also in the smooth muscles of the gastrointestinal tract (GIT), which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body.
  • The M4 muscarnic receptors: Postganglionic cholinergic nevers, possible CNS effects
  • The M5 Possible effects CNS

In anatomy, the atrium (plural: atria) is the blood collection chamber of a heart. ... The sinoatrial node (abbreviated SA node, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart. ... The atrioventricular node (abbreviated AV node) is the tissue between the atria and the ventricles of the heart, which conducts the normal electrical impulse from the atria to the ventricles. ... The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... Bronchoconstriction is the constriction of the airways in the lungs due to the tighting of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. ... The gastrointestinal tract (GI tract), also called the digestive tract, alimentary canal, or gut, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. ... The salivary glands produce saliva, which keeps the mouth and other parts of the digestive system moist. ...

References

  • Rhoades RA and Tanner GA, eds. (2003) Medical Physiology, 2nd ed. Lippincott, Williams and Wilkins. ISBN 0-7817-1936-4
  • University of Sydney lecture notes.

See also

Autonomic nervous system innervation, showing the sympathetic and parasympathetic (craniosacral) systems, in red and blue, respectively Parasympathetic ganglia are the autonomic ganglia of the parasympathetic nervous system. ...

External links

  • Image at uiuc.edu

  Results from FactBites:
 
The Parasympathetic Nervous System (2042 words)
The sympathetic system, on the other hand, is more mature at birth, and this evolutionary strategy enables the organism to be shaped by its interaction with the environment, which is mediated by mobilization behavior of the SNS (Schore, 1994).
The gradual maturation of the parasympathetic system is associated with the capacity to inhibit sympathetic activity, and results in a reduction in mobilization and baseline levels of arousal.
Parasympathetic activity is associated with inhibition of the intrinsic pacemaker of the heart, and results in a lower resting heart rate.
  More results at FactBites »

 
 

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