Sites Of Action

• Autonomic nervous system

(1) Parasympathetic division: ganglia; postganglionic endings (all)

(2) Sympathetic division: ganglia; a minority of postganglionic endings, e.g. sweat glands

• Neuromuscular junction

• Central nervous system

• Noninnervated sites: blood vessels, chiefly arterioles.

Acetylcholine is the neurotransmitter at all these sites, acting on a postsynaptic receptor, except on most blood vessels in which the action of cholinergic drugs is unrelated to cholinergic 'vasodilator' nerves. It is also produced in tissues unrelated to nerve endings, e.g. placenta and ciliated epithelial cells, where it acts as a local hormone (autacoid) on local receptors.

A list of principal effects is given below. Not all occur with every drug and not all are noticeable at therapeutic doses. For example, central nervous system effects of cholinergic drugs are best seen in cases of anticholinesterase poisoning. Atropine antagonises all the effects of cholinergic drugs except nicotinic actions on autonomic ganglia and the neuromuscular junction; i.e. it has antimuscarinic but not antinicotinic effects (see below).

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