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  • ACh: acetylcholine

  • AChE: acetylcholinesterase

  • BuChE: butyrylcholinesterase

  • CaM: calmodulin

  • CGRP: calcitonin gene-related peptide

  • CHT1: choline transporter

  • COMT: catechol-O-methyltransferase

  • DA: dopamine

  • DAT: DA transporter

  • DβH: dopamine β-hydroxylase

  • DOMA: 3,4-dihydroxymandelic acid

  • DOPEG: 3,4-dihydroxyphenyl glycol

  • DOPGAL: dihydroxyphenylglycolaldehyde

  • ENS: enteric nervous system

  • ENT: extraneuronal transporter

  • EPI: epinephrine

  • EPSP: excitatory postsynaptic potential

  • ICC: interstitial cells of Cajal

  • GABA: γ-aminobutyric acid

  • GI: gastrointestinal

  • GPCR: G protein-coupled receptor

  • 5HT: serotonin (5-hydroxytryptamine)

  • ICC: interstitial cells of Cajal

  • IP3: inositol 1,4,5-trisphosphate

  • IPSP: inhibitory postsynaptic potential

  • KO: knockout

  • mAChR: muscarinic acetylcholine receptor

  • MAO: monoamine oxidase

  • MAPK: mitogen-activated protein kinase

  • MOPEG: 3-methyl,4-hydroxyphenylglycol

  • MOPGAL: monohydroxyphenylglycolaldehyde

  • nAChR: nicotinic ACh receptor

  • NE: norepinephrine (noradrenaline)

  • NET: norepinephrine transporter

  • NMJ: neuromuscular junction (of skeletal muscle)

  • NO: nitric oxide

  • NOS: nitric oxide synthase

  • NPY: neuropeptide Y

  • NSF: N-ethylmaleamide sensitive factor

  • PACAP: pituitary adenylyl cyclase–activating peptide

  • PK_: protein kinase _, as in PKA

  • PL_: phospholipase _, as in PLA2, PLC, etc.

  • PNMT: phenylethanolamine-N-methyltransferase

  • SA: sinoatrial

  • SLC: solute carrier

  • SNAP: soluble NSF attachment protein, synaptosome-associated protein

  • SNARE: SNAP receptor

  • SST: somatostatin

  • STN: solitary tract nucleus

  • TH: tyrosine hydroxylase

  • VIP: vasoactive intestinal polypeptide

  • VMA: vanillyl mandelic acid

  • VMAT2: vesicular uptake transporter


The autonomic nervous system, also called the visceral, vegetative, or involuntary nervous system, is distributed widely throughout the body and regulates autonomic functions that occur without conscious control. In the periphery, it consists of nerves, ganglia, and plexuses that innervate the heart, blood vessels, glands, other visceral organs, and smooth muscle in various tissues. This system enables the body to constantly monitor, analyze, and anticipate needs, and control the response to the organ systems, in order to maintain homeostasis.

Differences Between Autonomic and Somatic Nerves

  • The efferent nerves of the autonomic nervous system supply all innervated structures of the body except skeletal muscles, which are served by somatic nerves.

  • The most distal synaptic junctions in the autonomic reflex arc occur in ganglia that are entirely outside the cerebrospinal axis. Somatic nerves contain no peripheral ganglia, and the synapses are located entirely within the cerebrospinal axis.

  • Many autonomic nerves form extensive peripheral plexuses; such networks are absent from the somatic system.

  • Postganglionic autonomic nerves generally are nonmyelinated; motor nerves to skeletal muscles are myelinated.

  • When the spinal efferent nerves are interrupted, smooth muscles and glands generally retain some level of spontaneous activity, whereas the denervated skeletal muscles are paralyzed.

Sensory Information: Afferent Fibers and Reflex Arcs

Afferent fibers from visceral structures are the first link in the reflex arcs of the autonomic system. With certain exceptions, such as local axon reflexes, most visceral reflexes are mediated through the CNS.

Visceral Afferent Fibers

Information on the status of the visceral organs is transmitted to the CNS through two main sensory systems: ...

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