NEUROMUSCULAR JUNCTION

also called Myoneural Junction, site of chemical communication between a nerve fibre and a muscle cell. It is analogous to the synapse between two neurons. A nerve fibre divides into many terminal branches, each terminal ending on a region of muscle fibre called the end-plate. Embedded in the end-plate are thousands of receptors, which are long protein molecules that form channels through the membrane. Upon stimulation by a nerve impulse, the terminal releases a chemical neurotransmitter (acetylcholine) from spheres called synaptic vesicles. The neurotransmitter then binds to the receptors, the channels open, and sodium ions flow into the end-plate. This initiates the end-plate potential (q.v.), the electric event that leads to contraction of the muscle fibre.