nAChRs (nicotinic acetylcholine receptors) are neuron receptor proteins that signal for muscular contraction upon a chemical stimulus. They are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the presynaptic and postsynaptic sides of theneuromuscular junction. Nicotinic acetylcholine receptors are the best-studied of the ionotropic receptors. Like the other type of acetylcholine receptor-the muscarinic acetylcholine receptor (mAChR)-the nAChR is triggered by the binding of the neurotransmitter acetylcholine (ACh). Just as muscarinic receptors are named such because they are also activated by muscarine, nicotinic receptors can be opened not only by acetylcholine but also by nicotine —hence the name "nicotinic".