ULTRASTRUCTURE OF NEUROMUSCULAR JUNCTIONS OF HUMAN RED, WHITE AND INTERMEDIATE STRIATED MUSCLE FIBERS

An electron microscopic study was made on the fine structural differences in the motor endplates among the red, white and intermediate muscle fibers of the human intercostal muscles and the following results were obtained: 1) In the motor endplate of the red fiber, the junctional folds appear on the whole as simple comparatively unbranched folds, while in that of the white one they are branched and anastomosed in a complicated manner. In the motor endplate of the intermediate fiber, the character of the folds is intermediate between those of the red and white fibers. 2) The sarcoplasmic area where the axonbranchlet is situated is apparently narrower in the red fiber than in the white or intermediate fibers. 3) The terminal branchlet in the red fiber is oval in shape but in the white one it has a concavity oriented towards the underlying muscle fiber. In the intermediate fiber the branchlet is intermediate between those of the red and white fibers. © 1969, Tohoku University Medical Press. All rights reserved.