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Sliding filament model
Process of movement
Myosin is a molecular motor that acts like an active ratchet. Chains of actin proteins form high tensile passive 'thin' filaments that transmit the force generated by myosin to the ends of the muscle. Myosin also forms 'thick' filaments. Each myosin 'paddles' along an actin filament repeatedly binding, ratcheting and letting go, sliding the thick filament over thin filament.
All real muscle cells are composed of a number of actin and myosin filaments in series. The basic unit is called the sarcomere. It consists of a central bidirectional thick filament flanked by two actin filaments, orientated in opposite directions. When each end of the myosin thick filament ratchets along the actin filament with which it overlaps, the two actin filaments are drawn closer together. Thus, the ends of the sarcomere are drawn in and the sarcomere shortens. Sarcomeres are connected together by so-called 'Z lines', which anchor the ends of actin filaments in such a way that the filaments on each side of the Z line point in opposite directions. By this means, sarcomeres are arranged in series. When a muscle fiber contracts, all sarcomeres contract simultaneously so that force is transmitted to the fiber ends.
Pre-process of movement
If the process of movement were to continue constantly, all muscles would constantly be contracted. Therefore, the body needs a way to control the ability of myosin to bind to the actin. This is accomplished by the introduction of calcium into the cytoplasm of the muscle cell.
Nerve impulses affect the way in which calcium bonds to the troponin.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sliding_filament_model". A list of authors is available in Wikipedia.|