Ultrastructure of Myotendinous Junction for Muscle Tension in Mouse Gastrocnemius

We examined the ultrastructure of myotendinous junction in the tendon bundle and aponeurosis areas of mouse gastrocnemius. In the tendon bundle area, a finger-shape invaginated junction was observed myofibril and collagenous fiber. Basement membrane and sacroplasm membrane were found in collagenous fiber and myofibril, respectively, and actin filament of the end of the myotome (Z Iine) connected with sacroplasm membrane. In the aponeurosis area, protruding tendon bundles appeared in the acute angle from the aponeurosis, with a similar connection structure to the tendon bundle area. Muscle fibers run obliquely at various angles to the long axis of the muscle, making a connection of tendon bundles. Gastrocnemius lacks in changes of contraction as an antigravity muscle, but has an effective muscle design for producing the maxi-mum muscle tension.