Each nicotinic acetylcholine receptor is a pentameric glycoprotein complex composed of five subunits, alpha, beta, delta and epsilon in a ratio of 2:1:1:1. These subunits are integral membrane proteins, spannning the cell membrane. Each of the two alpha subunits acts as a high-affinity acetylcholine-binding site. When stimulated, the channel undergoes conformational change and opens for one millisecond, allowing non-selective passage of small positively charged ions, mainly sodium, potassium and calcium. The Na+ influx depolarises nearby muscle membrane, triggering local voltage-gated Na+ channels, thereby creating a self-propagating depolarisation.
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