THE NEUROMUSCULAR JUNCTION

Formation of Neurotransmitter at Motor Nerve Endings

The axon of the motor nerve carries electrical signals from the spinal cord to the muscles and has all of the biochemical apparatus needed to transform the electrical signal into a chemical one. All the ion channels, enzymes, other proteins, macromolecules, and membrane components needed by the nerve ending to synthesize, store, and release acetylcholine and other trophic factors are made in the cell body and are transmitted to the nerve ending by axonal transport^{[10] [25]} ( Fig. 22-2 ). The simple molecules choline and acetate are obtained from the environment of the nerve ending, the former by a special system that transports it from the extracellular fluid to the cytoplasm and the latter in the form of acetyl coenzyme A from mitochondria. The enzyme choline acetyltransferase brings about the reaction of choline and acetate to form acetylcholine, which is stored in cytoplasm until it is transported into vesicles, which are in a better position for release.