endplate, end-plate

The ending of a motor nerve fiber in relation to a skeletal muscle fiber.

- motor e. the large and complex end-formation by which the axon of a motor neuron establishes synaptic contact with a striated muscle fiber (cell); several terminal branches of a motor axon end in irregular, club-shaped synaptic end-formations that are bedded in a single troughlike depression of the muscle fiber's surface; the postsynaptic membrane, the sarcolemma that forms the bottom of the trough, is greatly increased in surface area by deep infoldings protruding into the underlying cytoplasm of the muscle fiber; the subsynaptic interval between the plasma membrane of the axon terminals and the sarcolemma is filled with an amorphous substance; the trough is closed off toward the surface by the Schwann sheath, which peels away from the axons as the latter enter the trough and thus forms a lid over the trough; the slight bulge of this closure plate corresponds to Doyère eminence. SYN: sole-plate ending.