Scanning electron-microscopic study on the three-dimensional structure of motor endplates of the slow (tonic) muscle fibers in the frog, Rana n. nigromaculata

Summary

The three-dimensional organization of the motor endplates of the slow fibers of the rectus abdominis muscle in the Japanese meadow frog (Rana nigromaculata nigromaculata Hallowell) is visualized by use of a field-emission scanning electron microscope after removal of connective tissue components by HCl hydrolysis. Clusters of shallow oval depressions ∼1–3 μm in diameter are seen in the postsynaptic membrane at intervals of about 150 μm. On the surface of these depressions, a few low bulges of postsynaptic membrane are irregularly arranged. Terminal boutons, ∼1–3 μm in diameter, occur along the length of nerve branches and terminals and fit into the shallow oval depressions of the postsynaptic membrane. The Schwann cells covering the terminal branches exhibit a simpler organization than those in twitch fibers.