The Sliding Filament Theory

The Sliding Filament Theory

The sarcomere is the basic unit of the muscle fiber. It is a repeat unit within the myocytes responsible for the contractile action of the skeletal and cardiac muscles. The sarcomere consists of actin and myosin bundles. The myosin bundles contain thick filaments, while the action contains thin filaments. The myosin is flanked and interdigitated with the actin bundles. The interdigitation of the thick and the thin bundles gives the sarcomere, and the muscle at large, its striated appearance. The arrangement of the actin and myosin yields a band-like structure that has traditionally been described as light and dark bands upon visualization through a microscope.

The markings that have been described therein include the A bands, predominantly myosin fibers, and I-bands, which are actin-containing. These bands fuse to form a multinucleated myotube. At the central position of each A-band is a specialized region known as the M-line. It contains a muscle called myomesin, marks the center of the sarcomere, and is thought to be the starting point of a series of connections forming a muscle fiber. The Z disc is an area that transverses the I bands and forms the point of connection between two adjacent actin filaments. The Z disc and the M-band anchors the myosin and actin filaments to an elastic filaments system composed of the titin proteins (Wang et al., 2021).

Muscular contraction is preceded by the contractile changes in the sarcomere. The sliding filament theory attempts to describe the mechanism behind muscle contraction (Powers et al., 2021). Per the theory, sliding of the actin filaments above the myosin filaments generates an active force that causes muscles to contract. During muscle contraction, the sarcomere will shorten as the actin filament slides above the myosin filaments toward its center, then relax as the actin is released. This cycle is then repeated, forming a dance-like movement.

References

Powers, J. D., Malingen, S. A., Regnier, M., & Daniel, T. L. (2021). The sliding filament theory since Andrew Huxley: Multiscale and multidisciplinary muscle research. Annual Review of Biophysics, 50(1), 373–400. https://doi.org/10.1146/annurev-biophys-110320-062613

Wang, Z., Grange, M., Wagner, T., Kho, A. L., Gautel, M., & Raunser, S. (2021). The molecular basis for sarcomere organization in vertebrate skeletal muscle. Cell, 184(8). https://doi.org/10.1016/j.cell.2021.02.047

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Initial Post Instructions
Skeletal and cardiac muscle tissues contract via a process known as the sliding filament theory. To create these contractions, the muscle must be arranged in a specific pattern known as a sarcomere.

The Sliding Filament Theory

Discuss the different components of the sarcomere, how they are arranged, and what changes (if any) happen to them when the muscle is contracted.

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