Neuromuscular junction
In the body skeletal muscles undergo contraction only when they are stimulated through somatic efferent nerves. The nerve impulse is conducted along the nerve to the termination at the muscle fiber in the area of the highly developed neuromuscular junction. There is no direct connection between the nerve fiber ending and muscle, and the transmission of excitation is brought about through a chemical action. The chemical transmitter is acetylcholine (ACh). The events occur in the following sequence: when a nerve impulse reaches the neuromuscular junction, ACh is liberated from small storage areas in the nerve endings, called vesicles. The ACh then crosses the space between the nerve ending and the membrane of the muscle fiber (sarcolemma), causing an excitation of the muscle fiber, which results in contraction.