Rattlesnake shaker muscle: II. Fine structure.
The shaker muscle of the rattlesnake is able to sustain a rate of contraction around 50/sec for at least 3 hr. Most of the muscle is composed of a single, major fiber type which contains large numbers of small myofibrils, abundant sarcomplasmic reticulum, numerous mitochondria, and large deposits of glycogen. The neuromuscsular junction of the major fiber type is extensive with several nerve terminal expansions and junctional folds that are both numerous and deep. The structure of the major fiber type suggests that it must be responsible both for the speed of contraction as well as for the indefatigability of the shaker muscle. The ultrastructure of the much less numerous minor fibers in the shaker muscle suggest that their role may be a tonic one.
D000818:Animals; D003599:Cytoskeleton / Q000648:ultrastructure; D008854:Microscopy, Electron; D008931:Mitochondria, Muscle / Q000648:ultrastructure; D009119:Muscle Contraction; D009132:Muscles / Q000648:ultrastructure*; D009210:Myofibrils / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure; D012911:Snakes / Q000033:anatomy & histology*