Motor End Plate

motor end plate [′mōd·ər ′end ‚plāt]

(anatomy)

A specialized area beneath the sarcolemma where functional contact is made between motor nerve fibers and muscle fibers.

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Motor End Plate 

(also called end plate or motor end apparatus), a structural formation in vertebrate animals and humans on transversely striated muscle fiber at the point where the motor nerve ends. The motor end plate is the basic component of a nerve-muscle junction, which functions as a synapse with chemical transmission; a stimulus is transmitted from nerve to muscle by means of a mediator, and it contracts. The motor nerve loses its myelin sheath at the point of departure of its terminal branch, which forms a number of separate contacts with the surface of the muscle fiber. In the region of these contacts the nerve fiber contains so-called synaptic sacs—mitochondria—and is separated from the membrane of the muscle fiber, which has a folded structure, by a gap approximately 500 angstroms wide. The nerve ending in the region of the motor end plate is surrounded by a Schwann’s cell, which in some sections penetrates the gap between the membranes of the nerve and muscle fibers. (See Figure 1.)

Figure 1. Diagram of the structure of a motor end plate: (1) motor nerve, (2) myelin sheath, (3) cytoplasm of the Schwann’s cell, (4) processes of the Schwann’s cell that penetrate the gap between the nerve and muscle fibers, (5) nerve ending, (6) mitochondria, (7) synaptic sac, (8) muscle fiber, (9) folds of the membrane surrounding the muscle fiber, (10) solid band In the gap between the nerve and muscle fibers (the gap is shown by the arrows)

L. N. D’IACHKOVA