Editing Sympathetic nervous system (section)

==Structure==
There are two kinds of [[neurons]] involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter [[preganglionic neurons]] originate in the [[thoracolumbar division]] of the [[spinal cord]] specifically at [[thoracic vertebrae|T1]] to [[lumbar vertebrae|L2~L3]], and travel to a [[ganglion]], often one of the [[paravertebral ganglia]], where they synapse with a postganglionic neuron. From there, the long [[postganglionic fibers|postganglionic neurons]] extend across most of the body.<ref name="drake">{{cite book |vauthors = Drake RL, Vogl W, Mitchell AM, Gray H |title=Gray's Anatomy for Students  |url=https://books.google.com/books?id=SJBqAAAAMAAJ |edition=1 |publisher=Elsevier |year=2005 |pages=76–84 |isbn=0-443-06612-4}}</ref>

At the synapses within the ganglia, preganglionic neurons release [[acetylcholine]], a [[neurotransmitter]] that activates [[nicotinic acetylcholine receptors]] on postganglionic neurons. In response to this stimulus, the postganglionic neurons release [[norepinephrine]], which activates [[adrenergic receptors]] that are present on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system. However, there are three important exceptions:<ref name="pharma">{{cite book |vauthors = Rang HP, Dale MM, Ritter JM, Flower RJ |title=Rang and Dale's Pharmacology |url=https://books.google.com/books?id=mtNy9DgYCIgC&q=0443069115 |edition=6 |publisher=Elsevier |year=2007 |pages=135 |isbn=978-0-443-06911-6}}</ref>

# Postganglionic neurons of [[sweat gland]]s release acetylcholine for the activation of [[muscarinic receptors]], except for areas of thick skin, the palms and the plantar surfaces of the feet, where norepinephrine is released and acts on adrenergic receptors. This leads to the activation of [[sudomotor]] function, which is assessed by [[electrochemical skin conductance]].
# [[Chromaffin cells]] of the [[adrenal medulla]] are analogous to post-ganglionic neurons; the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion. Within this [[endocrine gland]], pre-ganglionic neurons synapse with chromaffin cells, triggering the release of two transmitters: a small proportion of [[norepinephrine]], and more substantially, [[epinephrine]]. The synthesis and release of epinephrine as opposed to norepinephrine is another distinguishing feature of chromaffin cells compared to postganglionic sympathetic neurons.<ref name="silverthorn">{{cite book |first=Dee Unglaub |last=Silverthorn |title=Human Physiology: An Integrated Approach |url=https://books.google.com/books?id=32dHPgAACAAJ&q=0321541308 |edition=4 |publisher=Pearson/Benjamin Cummings |year=2009 |pages=379–386 |isbn=978-0-321-54130-7}}</ref>
# Postganglionic sympathetic nerves terminating in the [[kidney]] release [[dopamine]], which acts on [[dopamine D1 receptor]]s of blood vessels to control how much blood the kidney filters. [[Dopamine]] is the immediate metabolic precursor to [[norepinephrine]], but is nonetheless a distinct signaling molecule.<ref name="cuevas">{{cite journal | vauthors = Cuevas S, Villar VA, Jose PA, Armando I | title = Renal dopamine receptors, oxidative stress, and hypertension | journal = Int J Mol Sci | volume = 14 | issue = 9 | pages = 17553–72 | date = August 2013 | pmid = 23985827 | pmc = 3794741 | doi = 10.3390/ijms140917553 | doi-access=free  }}</ref>

===Organization===
[[File:Gray838.png|thumb|The sympathetic nervous system extends from the thoracic to lumbar [[vertebra]]e and has connections with the thoracic, abdominal, and pelvic plexuses.]]

Sympathetic nerves arise from near the middle of the [[spinal cord]] in the [[intermediolateral nucleus]] of the [[lateral grey column]], beginning at the first [[thoracic]] [[vertebra (anatomy)|vertebra]] of the [[vertebral column]] and are thought to extend to the second or third [[lumbar]] vertebra. Because its cells begin in the thoracolumbar division – the thoracic and lumbar regions of the spinal cord – the sympathetic nervous system is said to have a ''thoracolumbar outflow''. [[Axon]]s of these nerves leave the spinal cord through the [[anterior root of spinal nerve|anterior root]].  They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through [[white rami]] connectors (so called from the shiny white sheaths of [[myelin]] around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) [[ganglion|ganglia]] extending alongside the spinal column.

To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through [[synaptic transmission]]. The ends of the axons link across a space, the [[synapse]], to the [[dendrites]] of the second cell.  The first cell (the presynaptic cell) sends a [[neurotransmitter]] across the synaptic cleft, where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.

[[File:Gray799.svg|thumb|Scheme showing structure of a typical [[spinal nerve]]. 1. Somatic efferent. 2. Somatic afferent. 3,4,5. Sympathetic efferent. 6,7. Sympathetic afferent.]]
Presynaptic nerves' axons terminate in either the [[paravertebral ganglia]] or [[prevertebral ganglia]]. There are four different paths an axon can take before reaching its terminal. In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve. After this, it can then either synapse in this ganglion, ascend to a more superior or descend to a more inferior paravertebral ganglion and synapse there, or it can descend to a prevertebral ganglion and synapse there with the postsynaptic cell.<ref>{{cite web |title=Divisions of the autonomic nervous system - sympathetic division pathways |url=https://content.byui.edu/file/a236934c-3c60-4fe9-90aa-d343b3e3a640/1/module10/readings/divisions_nerve_system.html#:~:text=The%20cell%20bodies%20of%20the,and%20enter%20a%20spinal%20nerve. |publisher=[[Brigham Young University–Idaho]] |access-date=31 March 2023 |archive-url=https://web.archive.org/web/20230218104009/https://content.byui.edu/file/a236934c-3c60-4fe9-90aa-d343b3e3a640/1/module10/readings/divisions_nerve_system.html |archive-date=18 February 2023}}</ref>

The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.).  Because paravertebral and prevertebral ganglia are close to the spinal cord, presynaptic neurons are much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.

A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) medulla.  In this case, presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the bloodstream.

In the sympathetic nervous system and other peripheral nervous system components, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a [[postganglionic]] cell. As mentioned previously, the preganglionic cells of the sympathetic nervous system are located between the first thoracic segment and the third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.

The ganglia include not just the sympathetic trunks but also the [[cervical ganglia]] ([[superior cervical ganglion|superior]], [[middle cervical ganglion|middle]] and [[inferior cervical ganglion|inferior]]), which send sympathetic nerve fibers to the head and thorax organs, and the [[celiac ganglion|celiac]] and [[mesenteric ganglion (disambiguation)|mesenteric ganglia]]<!--intentional link to DAB page-->, which send sympathetic fibers to the gut.

{{Table of autonomic innervation of organs}}

===Information transmission===
[[File:Sympathetic Nervous System.jpg|thumb|223x223px|Sympathetic nervous system – Information transmits through it affecting various organs.]]
[[Messages]] travel through the sympathetic nervous system in a bi-directional flow. [[efferent nerve fiber|Efferent]] messages can simultaneously trigger changes in different body parts. For example, the sympathetic nervous system can accelerate [[heart rate]]; widen [[bronchial]] passages; decrease [[motility]] (movement) of the [[large intestine]]; constrict blood vessels; increase [[peristalsis]] in the [[oesophagus]]; cause [[pupillary dilation]], piloerection ([[goose bumps]]) and perspiration ([[sweating]]); and raise blood pressure. One exception is with certain blood vessels, such as those in the cerebral and coronary arteries, which dilate (rather than constrict) with increased sympathetic tone. This is because of a proportional increase in the presence of β<sub>2</sub> adrenergic receptors rather than α<sub>1</sub> receptors. β<sub>2</sub> receptors promote vessel dilation instead of constriction like α1 receptors. An alternative explanation is that the primary (and direct) effect of sympathetic stimulation on coronary arteries is vasoconstriction followed by a secondary vasodilation caused by the release of vasodilatory metabolites due to the sympathetically increased cardiac inotropy and heart rate. This secondary vasodilation caused by the primary vasoconstriction is termed functional sympatholysis, the overall effect of which on coronary arteries is dilation.<ref name="Klabunde">{{cite book | vauthors=Klabunde RE | title=Cardiovascular physiology concepts | publisher=Lippincott Williams & Wilkins/Wolters Kluwer | publication-place=Philadelphia, PA | date=2012 | isbn=978-1-4511-1384-6 | oclc=712765593 | language=hu | page=160}}</ref>
The target synapse of the postganglionic neuron is mediated by [[adrenergic receptors]] and is activated by either [[norepinephrine]] (noradrenaline) or [[epinephrine]] (adrenaline).