Editing Acetylcholine (section)

===Autonomic nervous system===

[[File:1503 Connections of the Parasympathetic Nervous System.jpg|thumb|right|Components and connections of the [[parasympathetic nervous system]].]]
The [[autonomic nervous system]] controls a wide range of involuntary and unconscious body functions. Its main branches are the [[sympathetic nervous system]] and [[parasympathetic nervous system]]. Broadly speaking, the function of the sympathetic nervous system is to mobilize the body for action; the phrase often invoked to describe it is [[fight-or-flight response|fight-or-flight]]. The function of the parasympathetic nervous system is to put the body in a state conducive to rest, regeneration, digestion, and reproduction; the phrase often invoked to describe it is "rest and digest" or "feed and breed". Both of these aforementioned systems use acetylcholine, but in different ways.

At a schematic level, the sympathetic and parasympathetic nervous systems are both organized in essentially the same way: preganglionic neurons in the central nervous system send projections to neurons located in autonomic ganglia, which send output projections to virtually every tissue of the body. In both branches the internal connections, the projections from the central nervous system to the autonomic ganglia, use acetylcholine as a neurotransmitter to innervate (or excite) ganglia neurons. In the parasympathetic nervous system the output connections, the projections from ganglion neurons to tissues that do not belong to the nervous system, also release acetylcholine but act on muscarinic receptors. In the sympathetic nervous system the output connections mainly release [[noradrenaline]], although acetylcholine is released at a few points, such as the [[sudomotor]] innervation of the sweat glands.

==== Direct vascular effects ====
Acetylcholine in the [[Serum (blood)|serum]] exerts a direct effect on [[vascular tone]] by binding to [[Muscarinic acetylcholine receptor|muscarinic receptor]]s present on vascular [[endothelium]]. These cells respond by increasing production of [[nitric oxide]], which signals the surrounding smooth muscle to relax, leading to [[vasodilation]].<ref name="pmid15649880">{{cite journal | vauthors = Kellogg DL, Zhao JL, Coey U, Green JV | title = Acetylcholine-induced vasodilation is mediated by nitric oxide and prostaglandins in human skin | journal = J. Appl. Physiol. | volume = 98 | issue = 2 | pages = 629–32 | date = February 2005 | pmid = 15649880 | doi = 10.1152/japplphysiol.00728.2004 | s2cid = 293055 }}</ref>