This 3D animation shows the contraction of skeletal muscle fibers and the molecular events involved.
Striated muscle is made up of bundles of multinucleated muscle cells called myofibers. A myofiber is packed with myofibrils that extend the length of the cell.
A sarcomere, the functional and structural unit of muscle consists of thick myosin filaments and thin actin filaments.
Titin keeps thick filament centered during contraction. In muscle contraction actin filaments slide past myosin filaments. Neither filaments change in length yet the sarcomere becomes shorter.
The force required for this movement is generated by myosin heads which may cross bridge attachments to actin. Myosin heads walk along an actin filament using ATP for energy. Tropomyosin is part of the complex that prevents myosin from sliding along the thin filaments.
A myosin head binds ATP and as a result detaches from the actin filament. It rebinds in a new position.
Phosphate release triggers a power stroke that moves the actin filament. ADP disassociates and the process is repeated.
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