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Sliding filament theory: A sarcomere in relaxed (above) and contracted (below) positions. The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. [1]
A sarcomere (Greek σάρξ sarx "flesh", μέρος meros "part") is the smallest functional unit of striated muscle tissue. [1] It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called muscle fibers or myofibers) which are formed during embryonic myogenesis .
Sliding filament theory: A sarcomere in relaxed (above) and contracted (below) positions. The sliding filament theory describes a process used by muscles to contract. It is a cycle of repetitive events that cause a thin filament to slide over a thick filament and generate tension in the muscle. [22]
The calcium drives the movement of myosin and actin filaments. The sarcomere then shortens which causes the muscle to contract. [3] In the skeletal muscles connected to tendons that pull on bones, the mysia fuses to the periosteum that coats the bone. Contraction of the muscle will transfer to the mysia, then the tendon and the periosteum ...
Energy is released and stored in the myosin head to utilize for later movement. The myosin heads now return to their upright relaxed position. If calcium is present, the process is repeated. 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 sarcomere is attached to other organelles such as the mitochondria by intermediate filaments in the cytoskeleton. The costamere attaches the sarcomere to the sarcolemma. [5] Every single organelle and macromolecule of a muscle fiber is arranged to ensure that it meets desired functions.
ATP is required to reuptake calcium into the sarcomere's sarcoplasmic reticulum (SR). When a muscle is relaxed, the myosin heads are returned to their "high energy" position, ready and waiting for a binding site on the actin filament to become available. Because there is no ATP available, previously released calcium ions cannot return to the SR.
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]