They are fundamental components of the autonomic nervous system and are involved in multiple aspects of cognition and physiology.

There are five subtypes of muscarinic receptors (M1 through M5), each distributed in different tissues and serving different functions.

M1 receptors are found in the cerebral cortex and hippocampus and are involved in cognitive functions including learning and memory.

M2 receptors are in the heart and brainstem and regulate heart rate and breathing.

M3 receptors are in smooth muscle and glands, regulating salivation, digestion, and bronchial constriction.

M4 and M5 have more specialized distributions.