The Nicotinic Acetylcholine Receptors are members of a superfamily of ligand gated ion channels that mediate fast signal transmission at synapses. These receptors are thought to be hetero pentamers composed of homologous subunits. The proposed structure for each subunit is a conserved N terminal extracellular domain followed by three conserved transmembrane domains, a variable cytoplasmic loop, a fourth conserved transmembrane domain, and a short C terminal extracellular region. The Nicotinic Acetylcholine Receptor alpha 7 forms a homo oligomeric channel, displays marked permeability to calcium ions and is a major component of brain nicotinic receptors that are blocked by, and highly sensitive to, alpha bungarotoxin. Once this receptor binds acetylcholine, it undergoes an extensive change in conformation that affects all subunits and leads to opening of an ion conducting channel across the plasma membrane.