Acetylcholinesterase is type B carboxylesterase enzyme. A smaller concentration of the enzyme is found in the extrajunctional area. The enzyme is secreted from the muscle but remains attached to it by thin stalks of collagen fastened to the basement membrane. Most of the molecules of acetylcholine released from the nerve initially pass between the enzymes to reach the postjunctional receptors; however, as they are released from the receptors, they invariably encounter acetylcholinesterase and are destroyed. Under normal circumstances, a molecule of acetylcholine reacts with only one receptor before it is hydrolyzed. Acetylcholine is a potent messenger, but its actions are very short lived because it is destroyed in less than 1 ms after it is released.
