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the acetic acid ester of choline, normally present in many parts of the body and having important physiologic functions. It is a neurotransmitter at cholinergic synapses in the central, sympathetic, and parasympathetic nervous systems. Used in medicine as a miotic.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
a·ce·tyl·cho·line (ACH, Ach),(a-sē'til-kō'lēn),
The acetic ester of choline, the neurotransmitter substance at cholinergic synapses. It is hydrolyzed rapidly into choline and acetic acid by acetylcholinesterase in the tissues and by pseudocholinesterase in the blood.
Farlex Partner Medical Dictionary © Farlex 2012
A substance, C7H17NO3, that is derived from choline and is released at the ends of nerve fibers in the somatic and parasympathetic nervous systems, where it mediates the transmission of nerve impulses.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
AcetylcholineAn acetic acid ester which is a major cholinergic neurotransmitter released from neurones into the synaptic space after peripheral nervous system stimulation, mediating neuromuscular activity.
Action Vasodilation, cardiac inhibition, peristalsis, cognition, mood changes.
Reference value 0.02–0.20 mmol/L
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
acetylcholineNeurophysiology An acetic acid ester of choline-a substance that functions as a major cholinergic neurotransmitter released from vertebrate neurons into the synaptic spaces after stimulation from the PNS Action Vasodilation, cardiac inhibition, GI peristalsis; it is involved in the control of thought, mood, sleep, muscles, bladder, sweat glands
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
A neurotransmitter that stimulates nicotinic receptors in autonomic ganglia, at the motor endplates of skeletal muscle, and in the central nervous system as well as muscarinic receptors in smooth muscle, in exocrine glands, and in the central nervous system.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
acetylcholineThe acetic acid ester of choline, an important NEUROTRANSMITTER acting at cholinergic synapses to propagate nerve impulses. It occurs in both the brain and the peripheral nervous system and is the neurotransmitter at neuromuscular junctions. Acetylcholine is inactivated by the enzyme ACETYLCHOLINESTERASE, and drugs, such as physostigmine (Eserine) and edrophonium (Tensilon), that inhibit this enzyme, prolong the action of the neurotransmitter.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
acetylcholine (ACh)a TRANSMITTER SUBSTANCE that is secreted at the ends of CHOLINERGIC nerve fibres on the arrival of a NERVE IMPULSE. ACh then passes the impulse across a SYNAPSE and immediately ACh has depolarized the postsynaptic membrane it is destroyed by the enzyme CHOLINESTERASE. Compare ADRENERGIC.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
a molecule released by neurons at the neuromuscular junction that causes muscle contraction.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
A neurotransmitter substance with special excitatory properties of all preganglionic autonomic neurons, all parasympathetic postganglionic neurons and a few postganglionic sympathetic neurons. Acetylcholine is synthesized and liberated by the action of the enzyme choline acetyltranferase from the compounds choline and acetyl coenzyme A (acetyl CoA) which occurs in all cholinergic neurons. ACh exists only momentarily after its formation, being hydrolysed by the enzyme acetylcholinesterase which is present in the neurons of cholinergic nerves throughout their entire lengths and at neuromuscular junctions: this process is essential for proper muscle function as otherwise the accumulation of ACh would result in continuous stimulation of the muscles, glands and central nervous system. Alternatively a shortage of ACh has devastating effect (e.g. myasthenia gravis). ACh binds to acetylcholine receptors on skeletal muscle fibres. Sodium enters the muscle fibre membrane, which leads to a depolarization of the membrane and muscle contraction. There are two main types of acetylcholine receptors (cholinergic receptors): muscarinic receptors, which are stimulated by muscarine and ACh, belong to a family of G proteins coupled receptors and are situated in parasympathetically innervated structures (e.g. the iris and ciliary body); and nicotine receptors, which are stimulated by nicotine and ACh, are ligand-gated receptors and are situated in striated muscles (e.g. the extraocular muscles). Cholinergic receptors are found in the sympathetic and parasympathetic nervous systems, in the brain and spinal cord. The action of ACh can be either blocked or stimulated by drugs: Anticholinesterase drugs (e.g. neostigmine) inhibit acetylcholinesterase and prolong the action of acetylcholine whereas antimuscarinic drugs (also referred to as anticholinergics or parasympatholytics) such as atropine, cyclopentolate, homatropine, hyoscine and tropicamide inhibit the action of acetylcholine at muscarinic receptors. Other drugs mimic the action of ACh, they are known as parasympathomimetics (e.g. pilocarpine). See cholinergic; cycloplegia; miotics; mydriatic; neurotransmitter; nicotine; synapse; autonomic nervous system.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
Acetic ester of choline, the neurotransmitter substance at cholinergic synapses.
Medical Dictionary for the Dental Professions © Farlex 2012