premise: Muscarinic acetylcholine receptors are launch codes.
hypothesis: Muscarinic acetylcholine receptors , or mAChRs , are acetylcholine receptors that form G protein-receptor complexes in the cell membranes of certain neurons and other cells . They play several roles , including acting as the main end-receptor stimulated by acetylcholine released from postganglionic fibers in the parasympathetic nervous system . Their counterparts are nicotinic acetylcholine receptors ( nAChRs ) , receptor ion channels that are also important in the autonomic nervous system . Muscarinic antagonist . Acetylcholine ( often abbreviated ACh ) is a neurotransmitter whose receptor is a protein found in synapses and other cell membranes . Acetylcholine receptors are classified into two groups based on this :