acetylcholine (ACh)

acetylcholine (ACh)

a substance made in certain nerve cells and released from their axon terminals at a junction or synapse in the process of cholinergic transmission of impulses (1) from motor nerves to skeletal muscle, (2) from one nerve to another in the nervous system (in the brain, and in autonomic ganglia), (3) at parasympathetic nerve endings (e.g. those that slow down the heart rate, stimulate secretion from glands or activate smooth muscle in the gut). Cholinergic receptors occur in two different pharmacological groups: nicotinic, e.g. at skeletal muscle motor endplates, and muscarinic, e.g. in cardiac and smooth muscles. See also neuromuscular junction, neurotransmitter, parasympathetic nervous system.