Editing Sympathetic nervous system (section)

==Function==
{| class="wikitable" align="right" border="1"
|+ align="bottom" style="caption-side: bottom; font-weight: normal; font-style: italic; font-size: smaller;" | Examples of sympathetic system action on various organs<ref name="silverthorn" /> except where otherwise indicated.
|-
! Organ
! Effect
|-
| Eye
|Dilates [[pupil]]
|-
| Heart
| Increases rate and force of contraction
|-
| Lungs
| Dilates [[bronchioles]] via circulating adrenaline<ref name="Hlastala_Berger_2001">{{cite book | vauthors = Hlastala MP, Berger AJ| title=Physiology of respiration | publisher=Oxford University Press | publication-place=Oxford | date=2001 | isbn=0-19-513846-5 | oclc=44545198 | page=177}}</ref>
|-
| Blood vessels
| Dilates in skeletal muscle<ref>{{cite book | vauthors =Jänig W | title=The integrative action of the autonomic nervous system : neurobiology of homeostasis | publisher=Cambridge University Press | publication-place=Cambridge, UK | date=2006 | isbn=978-0-511-22617-5 | oclc=191696146|pages= 132–135}}</ref>
|-
|
| Constricts in gastrointestinal organs
|-
| [[Sweat gland]]s
| Activates [[sudomotor]] function and sweat secretion
|-
| Digestive tract
| Inhibits [[peristalsis]]
|-
| Kidney
| Increases [[renin]] secretion
|-
| Penis
|  Doesn't cause [[erection]]
|-
| [[Vas deferens|Ductus deferens]]
| Promotes emission prior to ejaculation
|-
|}

The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulation of functions as diverse as [[pupil]] diameter, [[gut motility]], and [[urinary system]] output and function.<ref name="Moro et al. 2013">{{cite journal | vauthors = Moro C, Tajouri L, Chess-Williams R | title = Adrenoceptor function and expression in bladder urothelium and lamina propria | journal = Urology | volume = 81 | issue = 1 | pages = 211.e1–7 | date = January 2013 | pmid = 23200975 | doi = 10.1016/j.urology.2012.09.011 }}</ref> It is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the ''fight-or-flight response''. This response is also known as ''sympatho-adrenal response'' of the body, as the [[preganglionic]] sympathetic fibers that end in the [[adrenal medulla]] (but also all other sympathetic fibers) secrete acetylcholine, which activates the great secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the [[cardiovascular system]] is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via [[catecholamines]] secreted from the adrenal medulla.

The sympathetic nervous system is responsible for priming the body for action, particularly in situations threatening survival.<ref name=":0">{{cite book |vauthors=Ornstein RE|title=The Evolution of Consciousness: of Darwin, Freud, and Cranial Fire: The Origins of the Way We Think |url=https://archive.org/details/evolutionofconsc0000orns |url-access=registration |publisher=Simon & Schuster |location=New York |year=1992 |isbn=0-671-79224-5 }}</ref> One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.

Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs due to the activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons. These receptors exist throughout the vasculature of the body but are inhibited and counterbalanced by beta-2 adrenergic receptors (stimulated by epinephrine release from the adrenal glands) in the skeletal muscles, the heart, the lungs, and the brain during a sympathoadrenal response. The net effect of this is a shunting of blood away from the organs not necessary to the immediate survival of the organism and an increase in blood flow to those organs involved in intense physical activity.

=== Sensation ===
The afferent fibers of the [[autonomic nervous system]], which transmit sensory information from the internal organs of the body back to the central nervous system (or CNS), are not divided into parasympathetic and sympathetic fibers as the efferent fibers are.<ref name="Moore_Agur_2007">{{cite book | vauthors = Moore KL, Agur AM| title=Essential clinical anatomy | publisher=Lippincott Williams & Wilkins | publication-place=Philadelphia, PA | date=2007 | isbn=978-0-7817-6274-8 | oclc=63279568 | pages=34–35}}</ref>  Instead, autonomic sensory information is conducted by [[general visceral afferent fibers]].

General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the [[Central nervous system|CNS]].  While the unconscious [[reflex arcs]] normally are undetectable, in certain instances they may send [[pain]] sensations to the CNS masked as [[referred pain]]. If the [[peritoneal cavity]] becomes inflamed or if the [[intestine]] is suddenly distended, the body will interpret the afferent pain stimulus as [[Somatic nervous system|somatic]] in origin. This pain is usually non-localized. The pain is also usually referred to [[Dermatome (anatomy)|dermatomes]] that are at the same spinal nerve level as the visceral afferent [[synapse]].{{citation needed|date=June 2013}}<!-- Likely the same source as previously (Moore's Essential Clinical Anatomy) but as I have no access to this source, I cannot check it.-->

===Relationship with the parasympathetic nervous system===
Together with the other component of the [[autonomic nervous system]], the parasympathetic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. Reaction to [[Stress (biology)|stress]]—as in the flight-or-fight response—is thought to be elicited by the sympathetic nervous system and to counteract the [[parasympathetic nervous system|parasympathetic system]], which works to promote maintenance of the body at rest. The comprehensive functions of both the parasympathetic and sympathetic nervous systems are not so straightforward, but this is a useful rule of thumb.<ref name="brodal" /><ref name="sherwood">{{cite book |vauthors =Sherwood L|title=Human Physiology: From Cells to Systems |url=https://books.google.com/books?id=gOmpysGBC90C&pg=PT268 |edition=7 |publisher=Cengage Learning |year=2008 |pages=240 |isbn=978-0-495-39184-5}}</ref>

=== Origins ===
It was originally believed that the sympathetic nervous system arose with [[Gnathostomata|jawed vertebrates]].<ref name="Nicol 1952 pp. 1–48">{{cite journal |last=Nicol |first=J. A. Colin |date=1952 |title=AUTONOMIC NERVOUS SYSTEMS IN LOWER CHORDATES |journal=Biological Reviews |volume=27 |issue=1 |pages=1–48 |doi=10.1111/j.1469-185X.1952.tb01361.x |issn=1464-7931}}</ref> However, the sea lamprey ([[Sea lamprey|Petromyzon marinus]]), a [[Agnatha|jawless vertebrate]], has been found to contain the key building blocks and developmental controls of a sympathetic nervous system.<ref name="Edens Stundl Urrutia Bronner 2024 pp. 121–126">{{cite journal |last1=Edens |first1=Brittany M. |last2=Stundl |first2=Jan |last3=Urrutia |first3=Hugo A. |last4=Bronner |first4=Marianne E. |date=2024 |title=Neural crest origin of sympathetic neurons at the dawn of vertebrates |journal=Nature |volume=629 |issue=8010 |pages=121–126 |doi=10.1038/s41586-024-07297-0 |pmid=38632395 |bibcode=2024Natur.629..121E |issn=0028-0836|pmc=11391089 }}</ref> [[Nature (journal)|Nature]] described this research as a "landmark study" that "point to a remarkable diversification of sympathetic neuron populations among vertebrate classes and species".<ref name="Ernsberger Rohrer 2024 pp. 46–48">{{cite journal |last1=Ernsberger |first1=Uwe |last2=Rohrer |first2=Hermann |date=2024 |title=The sympathetic nervous system arose in the earliest vertebrates |journal=Nature |volume=629 |issue=8010 |pages=46–48 |doi=10.1038/d41586-024-01017-4 |pmid=38632426 |bibcode=2024Natur.629...46E |issn=0028-0836}}</ref>