Describing one of the two main classes of acetylcholine receptors, so called because the effect of acetylcholine on them can be mimicked by muscarine, a toxic alkaloid produced by Amanita muscaria and certain other gill fungi. Muscarinic receptors occur on target cells innervated by fibres of the vertebrate parasympathetic nervous system, for example in smooth muscle, cardiac muscle, and glands. They are G protein-coupled receptors, which activate ion channels via intracellular second messengers. Compare nicotinic.