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H-band is the zone of the thick filaments that has no actin. Within the H-zone is a thin M-line (from the German "mittel" meaning middle), appears in the middle of the sarcomere formed of cross-connecting elements of the cytoskeleton. Molecular model of the Sarcomere in the A-band. Organization of the central region of the A-band (C-zone).
When a muscle contracts, the actin is pulled along myosin toward the center of the sarcomere until the actin and myosin filaments are completely overlapped. The H zone becomes smaller and smaller due to the increasing overlap of actin and myosin filaments, and the muscle shortens.
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during contraction, actin filaments move into the A bands and the H zone is filled up reducing its stretch, the I bands shorten, the Z line comes in contact with the A bands; and the possible driving force of contraction is the actin-myosin linkages which depend on ATP hydrolysis by the myosin.
Sarcomere diagram2.svg; Sarcomere es.svg; ... changed H band to H zone, so it is lesser confusing. 09:18, 19 June 2007: 1,350 × 1,044 (347 KB) Nainscription~commonswiki
The protein complex composed of actin and myosin, contractile proteins, is sometimes referred to as actomyosin.In striated skeletal and cardiac muscle, the actin and myosin filaments each have a specific and constant length in the order of a few micrometers, far less than the length of the elongated muscle cell (up to several centimeters in some skeletal muscle cells). [5]
The darker bands within skeletal muscle, known as anisotropic bands (A bands), encompass both thick and thin filaments and constitute the central region of the sarcomere, extending across the H-zone. Collectively, the A bands and the I bands create the distinctive striped appearance of skeletal muscle tissue. [ 3 ]
Sarcomere and M-band structure. [3] (a) electron micrograph of mouse heart muscle sarcomere. (b) diagram of sarcomere layout from (a). Myosin thick filaments are blue, thin actin filaments are orange, Z-discs are black, and the M-band is grey/white. (c) schematic of M-band composition of M-lines.