Nicotinic acetylcholine receptors (nAChRs) are a diverse group of membrane proteins found in many types of excitable tissue, including brain, autonomic ganglia, and muscle. Acetylcholine (ACh), the endogenous ligand for these receptors, binds to agonist sites on nAChRs, causing opening of an intrinsic transmembrane cation channel and depolarization of neurons or muscle cells. Muscle nAChRs mediate fast neuromuscular transmission. Cholinergic transmission in the autonomic nervous system (ANS) regulates cardiac output, vascular tone, body temperature, blood glucose, osmolality, respiration, and gastrointestinal tract activity. The roles of nAChRs in neurons and glial cells of the CNS are not fully defined, but they appear to play roles in many functions altered by anesthetics, including memory, arousal, and pain.