Fine Structure of Striated Muscle
نویسنده
چکیده
Much of the recent work on muscle fine structure has been discussed in a recent review by Bennett (1), who also covered the structure of various sarcoplasmic components and the sarcolemma. The present paper will be limited to myofibrillar fine structure. In the main, the current controversy in relation to muscle structure centers around two models, (a) what might be termed the "classical" model, in which a continuous skeletal framework of myofilaments traverses all bands of the sarcomere, the band pattern arising from interstitial materials, and (b) the interdigitating model advocated by Huxley and Hanson in various forms (13, 19, 27). In the latter model, the primary array of filaments in the A band of vertebrate muscle is identified as myosin I and the secondary array seen in transverse sections as actin filaments. The bulk of evidence appears to favour the classical type of model. The results to be discussed here support the concept that striated muscles from various sources have a similar basic structure, with variations adapted to the diversity of function found in nature. This structure appears to be of the classical type in that thin filaments (probably of actin) are found to traverse all bands in continuous array. Myosin is localized in the A bands proper, and there is a good deal of evidence to support the presence in the A bands of another protein of low molecular weight and viscosity, which appears to be involved in the formation of contraction bands. In addition, the myofilaments are apparently linked together by a system of transverse filamentous bridges which are spaced 250 to 400 A apart along the fiber axis, the magnitude of the spacing depending on the state of contraction of the myofibrih
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