Muscarinic acetylcholine receptor

Muscarinic acetylcholine receptors are G protein-coupled receptors activated by acetylcholine. Five subtypes, M1 through M5, mediate diverse effects in the nervous system, glands, heart, and smooth muscle.

Acetylcholine: A neurotransmitter and signaling molecule that activates nicotinic and muscarinic receptors. It is the endogenous ligand that activates every muscarinic receptor subtype.
M1 muscarinic receptor: A muscarinic acetylcholine receptor subtype expressed prominently in the brain and also in peripheral tissues. M1 illustrates the excitatory, Gq-linked branch of the receptor family.
Atropine: A naturally occurring tropane alkaloid that competitively blocks muscarinic acetylcholine receptors. Its broad receptor blockade reveals muscarinic contributions to heart rate, secretion, and pupil size.
Nicotinic acetylcholine receptor: A ligand-gated ion channel activated by acetylcholine and nicotine. Unlike muscarinic receptors, it directly conducts ions rather than signaling through G proteins.
Cholinergic system: The network of neurons and processes that use acetylcholine as a signaling molecule. Muscarinic receptors are a major route through which this system affects target cells.
G protein-coupled receptor: A membrane receptor family that converts extracellular signals into intracellular responses through heterotrimeric G proteins. Muscarinic receptors belong to this large receptor superfamily.
M2 muscarinic receptor: A muscarinic acetylcholine receptor subtype found prominently in the heart and nervous system. M2 demonstrates how muscarinic signaling can slow cardiac activity.
Scopolamine: A tropane alkaloid that blocks muscarinic receptors and is used to prevent motion sickness. Its central antimuscarinic action helps prevent nausea caused by motion.
Cholinergic receptor: A receptor activated by acetylcholine, including muscarinic and nicotinic receptor families. Muscarinic receptors form one branch of the broader cholinergic receptor family.
Parasympathetic nervous system: A division of the autonomic nervous system that supports functions such as digestion, secretion, and energy conservation. Muscarinic receptors mediate many parasympathetic effects at target organs.

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