MOTOR NERVE ENDINGS OF TWITCH MUSCLE FIBERS IN HIPPOCAMPUS HUDSONIUS

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Abstract
The motor nerve endings of the twitch muscle fibers of Hippocampus hudsonius were studied by light and electron microscopy. The postsynaptic membrane was without the folds or invaginations which are characteristic of the sole plate of other twitch muscle fibers. The postsynaptic membrane was, however, similar to that found heretofore on many slow tonic muscle fibers in other species. The nerve endings were found in a shallow depression in the long axis of the muscle fiber and are approximately 0.75-1. 5 [mu] in diameter. The pre- and postsynaptic membranes were separated by a 750A space within which a basement membrane was found. The physiological significance of the extensive distribution of en grappe type motor nerve endings found in the Hippocampus dorsal fin musculature was discussed. The presence of multiple nerve endings appears to be the morphological basis for the observed mechanical activity of the dorsal fin musculature which is the sole means of propulsion of this unusual teleost which swims slowly in a vertical position.

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