M1 was expressed in the CNS such as cerebral cortex, basal ganglia, limbic areas, vestibular system and esophageal smooth muscle. Synaptic transmission by muscarinic acetylcholine receptors (mAChRs) is employed throughout the central and peripheral nervous systems to elicit a large and diverse array of neurophysiological actions. An important aspect of mAChR functional diversity is reflected by the multitude of biochemical and electrophysiological actions evoked by acetylcholine binding to mAChRs, which include the regulation of intracellular levels of cAMP, cGMP and inositol phospholipids, and the opening or closing of the potassium, calcium, and chloride ion channels found in certain tissues.