Editing Autonomic nervous system (section)

==Function==
[[File:The Autonomic Nervous System.jpg|thumb|Function of the autonomic nervous system<ref>[[Neil A. Campbell]], [[Jane B. Reece]]: Biologie. Spektrum-Verlag Heidelberg-Berlin 2003, {{ISBN|3-8274-1352-4}}</ref>]]

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. The sympathetic system is often considered the "[[Fight-or-flight response|fight or flight]]" system, while the parasympathetic system is often considered the "rest and digest" or "feed and breed" system.

However, many instances of sympathetic and parasympathetic activity cannot be ascribed to "fight" or "rest" situations. For example, standing up from a reclining or sitting position would entail an unsustainable drop in blood pressure if not for a compensatory increase in the arterial sympathetic tonus. Another example is the constant, second-to-second, modulation of heart rate by sympathetic and parasympathetic influences, as a function of the respiratory cycles. In general, these two systems should be seen as permanently modulating vital functions, in a usually antagonistic fashion, to achieve [[homeostasis#Neurotransmission|homeostasis]].
Higher organisms maintain their integrity via homeostasis which relies on negative feedback regulation which, in turn, typically depends on the autonomic nervous system.<ref>{{cite book | last1 = Goldstein | first1 = David | title = Principles of Autonomic Medicine | date = 2016 | url = https://neuroscience.nih.gov/publications/PrinciplesofAutonomicMedicine30.pdf | publisher = National Institute of Neurological Disorders and Stroke, National Institutes of Health | location = Bethesda, Maryland | isbn = 9780824704087 | edition = free online version | access-date = 2018-12-05 | archive-date = 2018-12-06 | archive-url = https://web.archive.org/web/20181206053244/https://neuroscience.nih.gov/publications/PrinciplesofAutonomicMedicine30.pdf | url-status = dead }}</ref>  Some typical actions of the sympathetic and [[parasympathetic nervous system]]s are listed below.<ref>{{Cite book|title=Life Sciences : Fundamentals and practice.|last=Pranav Kumar.|date=2013|publisher=Pathfinder Academy|others=Mina, Usha.|isbn=9788190642774|edition=3rd|location=New Delhi|oclc=857764171}}</ref>
{| class="wikitable"
|+
!Target organ/system
!Parasympathetic
!Sympathetic
|-
|Digestive system
|Increase peristalsis and amount of secretion by digestive glands
|Decrease activity of digestive system
|-
|Liver
|No effect
|Causes glucose to be released to blood
|-
|Lungs
|Constricts bronchioles
|Dilates bronchioles
|-
|Urinary bladder and Urethra
|Relaxes sphincter
|Constricts sphincter
|-
|Kidneys
|No effects
|Decrease urine output
|-
|Heart
|Decreases rate
|Increase rate
|-
|Blood vessels
|No effect on most blood vessels
|Constricts blood vessels in viscera; increase BP
|-
|Salivary and lacrimal glands
|Stimulates; increases production of saliva and tears
|Inhibits; result in dry mouth and dry eyes
|-
|Eye (iris)
|Stimulates constrictor muscles; constrict pupils
|Stimulate dilator muscle; dilates pupils
|-
|Eye (ciliary muscles)
|Stimulates to increase bulging of lens for close vision
|Inhibits; decrease bulging of lens; prepares for distant vision
|-
|Adrenal medulla
|No effect
|Stimulate medulla cells to secrete epinephrine and norepinephrine
|-
|Sweat gland of skin
|No effect
|Stimulate [[sudomotor]] function to produce perspiration
|}

===Sympathetic nervous system===
{{Main|Sympathetic nervous system}}
Promotes a [[fight-or-flight response]], corresponds with arousal and energy generation, and inhibits digestion
* Diverts blood flow away from the [[gastro-intestinal]] (GI) tract and [[skin]] via [[vasoconstriction]]
* Blood flow to [[skeletal muscle]]s and the [[lung]]s is enhanced (by as much as 1200% in the case of skeletal muscles)
* Dilates [[bronchioles]] of the lung through circulating [[epinephrine]], which allows for greater [[Pulmonary alveolus|alveolar]] oxygen exchange
* Increases [[heart rate]] and the [[contractility]] of cardiac cells ([[myocytes]]), thereby providing a mechanism for enhanced blood flow to skeletal muscles
* Dilates [[pupils]] and relaxes the [[ciliary muscle]] to the lens, allowing more light to enter the eye and enhances far vision
* Provides [[vasodilation]] for the [[coronary vessels]] of the [[heart]]
* Constricts all the intestinal [[sphincters]] and the urinary sphincter
* Inhibits [[peristalsis]]
* Stimulates [[orgasm]]
The pattern of innervation of the [[sweat gland]]—namely, the postganglionic [[Sympathetic nervous system|sympathetic nerve]] fibers—allows clinicians and researchers to use [[sudomotor]] function testing to assess dysfunction of the autonomic nervous systems, through [[electrochemical skin conductance]].

===Parasympathetic nervous system===
{{Main|Parasympathetic nervous system}}
The parasympathetic nervous system has been said to promote a "rest and digest" response, promotes calming of the nerves return to regular function, and enhancing digestion. Functions of nerves within the parasympathetic nervous system include:{{citation needed|date=November 2014}}
* Dilating blood vessels leading to the GI tract, increasing the blood flow.
* Constricting the bronchiolar diameter when the need for oxygen has diminished
* Dedicated cardiac branches of the [[vagus]] and thoracic [[Accessory nerve|spinal accessory]] nerves impart parasympathetic control of the [[heart]] ([[myocardium]])
* Constriction of the pupil and contraction of the [[ciliary muscle]]s, facilitating [[Accommodation (eye)|accommodation]] and allowing for closer vision
* Stimulating [[salivary gland]] secretion, and accelerates [[peristalsis]], mediating digestion of food and, indirectly, the absorption of nutrients
* Sexual. Nerves of the peripheral nervous system are involved in the erection of genital tissues via the [[pelvic splanchnic nerves]] 2–4. They are also responsible for stimulating sexual arousal.

===Enteric nervous system===
{{Main|Enteric nervous system}}
The enteric nervous system is the intrinsic nervous system of the [[gastrointestinal system]]. It has been described as the "second brain of the human body".<ref>{{Cite web|url=https://www.scientificamerican.com/article/gut-second-brain/|title=Think Twice: How the Gut's "Second Brain" Influences Mood and Well-Being|last=Hadhazy|first=Adam|website=Scientific American|date=February 12, 2010|url-status=live|archive-url=https://web.archive.org/web/20171231104047/https://www.scientificamerican.com/article/gut-second-brain/|archive-date=December 31, 2017}}</ref> Its functions include:
* Sensing chemical and mechanical changes in the gut
* Regulating secretions in the gut
* Controlling [[peristalsis]] and some other movements

===Neurotransmitters===
{{main|Table of neurotransmitter actions in the ANS|Non-noradrenergic, non-cholinergic transmitter}}
[[File:Autonomic nervous system.jpg|thumb|A flow diagram showing the process of stimulation of adrenal medulla that makes it release adrenaline, that further acts on adrenoreceptors, indirectly mediating or mimicking sympathetic activity]]
[[File:Sistema Nervioso Autonomo.svg|thumb]]

At the effector organs, sympathetic ganglionic neurons release [[noradrenaline]] (norepinephrine), along with other [[cotransmitters]] such as [[adenosine triphosphate|ATP]], to act on [[adrenergic receptors]], with the exception of the [[Sudomotor|sweat glands]] and the adrenal medulla:
* [[Acetylcholine]] is the preganglionic neurotransmitter for both divisions of the ANS, as well as the postganglionic neurotransmitter of parasympathetic neurons.  Nerves that release acetylcholine are said to be cholinergic.  In the parasympathetic system, ganglionic neurons use acetylcholine as a neurotransmitter to stimulate muscarinic receptors.
* At the [[adrenal medulla]], there is no postsynaptic neuron. Instead, the presynaptic neuron releases acetylcholine to act on [[nicotinic receptors]]. Stimulation of the adrenal medulla releases [[adrenaline]] (epinephrine) into the bloodstream, which acts on adrenoceptors, thereby indirectly mediating or mimicking sympathetic activity.

A full table is at [[Table of neurotransmitter actions in the ANS]].

===Autonomic nervous system and the immune system===
Recent studies indicate that ANS activation is critical for regulating the local and systemic immune-inflammatory responses and may influence acute stroke outcomes. Therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response could promote neurologic recovery after stroke.<ref name="pmid35766834">{{cite journal | vauthors = Zhu L, Huang L, Le A, Wang TJ, Zhang J, Chen X, Wang J, Wang J, Jiang C | title = Interactions between the Autonomic Nervous System and the Immune System after Stroke | journal = Compr Physiol | volume = 2022 | pages = 3665–3704 | date = June 2022 | issue = 3 | pmid = 35766834 | doi = 10.1002/cphy.c210047 | isbn = 9780470650714 }}</ref>