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Abbreviations
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
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ANATOMY AND GENERAL FUNCTIONS
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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.
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Differences Between Autonomic and Somatic Nerves
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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.
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Sensory Information: Afferent Fibers and Reflex Arcs
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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.
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Visceral Afferent Fibers
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Information on the status of the visceral organs is transmitted to the CNS through two main sensory systems: ...