ABSTRACT
The axon of a motor neuron divides into a number of branches at the surface of the muscle fiber. Each branch ends in a bouton which forms a synapse with the muscle fiber, called a neuromuscular junction (nmj). The cleft of the nmj (Figure 1) is about 50 nm across. The postjunctional membrane, the endplate, which is thrown into folds, has a high density of nicotinic acetylcholine receptors under the active zones where acetylcholine (ACh) is released. The cleft contains a collagenous basement membrane (basal lamina) to which is bound acetylcholinesterase (AChE). Soluble forms of the same enzyme are also secreted into the cleft.
