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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 explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. [1]
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 before causing the bone to move.
When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap. Contraction in more detail. Contraction is achieved by the muscle's structural unit, the muscle fiber, and by its functional unit, the motor unit. [4]
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]
A diagram of the structure of a myofibril (consisting of many myofilaments in parallel, and sarcomeres in series) Sliding filament model of muscle contraction. The myosin heads form cross bridges with the actin myofilaments; this is where they carry out a 'rowing' action along the actin. When the muscle fibre is relaxed (before contraction ...
Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Within the sarcomere, actin and myosin fibers overlap in a
The sarcoplasmic reticulum is a network of the tubules that extend throughout muscle cells, wrapping around (but not in direct contact with) the myofibrils (contractile units of the cell).