Acetylcholine receptor anatomy
The acetylcholine receptor (AChR) is a membrane protein that binds to the neurotransmitter acetylcholine (Ach). These receptors can be divided into two main types of distinct receptors, nicotinic and muscarinic. Nicotinic acetylcholine receptors (nAChR) are pentameric ligand-gated ion channels, whereas muscarinic acetylcholine receptors (mAChR) are seven-helix G-protein coupled membrane proteins.
The fetal or immature receptor is also referred to as “extrajunctional” because it can be located anywhere in the muscle membrane, inside or outside the neuromuscular junction. It consists of α, β, δ, and γ subunits; there are two subunits of α and one each of the others.
Finally, the ganglion type nicotinic receptor is a type of nicotinic acetylcholine receptor that is located in the autonomic ganglia.
Muscarinic acetylcholine receptors (mAChR) These receptors are seven transmembrane G-protein coupled receptors. The structure of the receptors varies between tissues and different times in development. There are five described subtypes of muscarinic receptors (M1-M5). mAChR play major role in the parasympathetic nervous system for diverse functions, including regulation of smooth muscle activity, wakefulness, hormone secretion, heart rate.