Acetylcholine

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Contents

Definition

Low molecular weight transmitter substance, the only one that is not an amino acid or directly derived from one. The biosynthetic pathway has only one enzymatic reaction catalyzed by choline acetyltransferase. The reactants or acetyl CoA and choline.

Choline cannot be synthesized by nervous tissue, and therefore must be derived from the diet and delivered to neurons.

Abbreviated as ACh.

Distribution

Used by motor neurons of the spinal cord, and is found at all neuromuscular junctions in vertebrates. In the ANS it is released by all preganglionic neurons, as well as postganglionic parasympathetic neurons and some postganglionic sympathetic neurons.

In the CNS, ACh it is used at many synapses. In particular, it is synthesized in the nucleus basalis, and the neurons have widespread projections to the cerebral cortex. In most regions of the CNS, the effects of ACh appear to be generated by interaction with a mixture of nicotinic and muscarinic receptors.

Inactivation

Mostly by enzymatic conversion to acetate and choline, catalyzed by acetylcholinesterase

Receptors

  • Nicotinic (neuromuscular junctions and autonomic ganglia)
  • Muscarinic (mostly in smooth muscle and glands)
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