What is the H Zone?

Located in the central part of the A band, the H zone is a skeletal muscle fiber composed of thick filaments. These filaments are myosin. During contraction, the H-Zone becomes less visible because of the absence of actin filaments. The area is also marked by a thin M-line.

The H-Zone is part of a larger complex, the sarcomeric H-zone complex. It is the result of a long-term process of remodeling the cytoskeleton in the brain, which is responsible for creating muscle fibers and organizing the cells into tissues. In vertebrates, it is probably a semi-linear structure. In invertebrates, it may be a giant titin-like scaffolding protein.

The H-Zone's'mood' is achieved by modifying the levels of calcium ions in the cell. This alters the structure of the tropomyosin protein, which covers the myosin binding sites on actin. Ca2+ ions force the tropomyosin to reveal a transverse bridge, which binds the actin and myosin proteins together. This changes the positioning of the actin and myosin filaments, which leads to more efficient muscle contraction.

The H-zone isn't as well-known as the I-band, although both contain the same function. The most important function of the H-Zone is to anchor myosin filaments into the A-band. A-bands, on the other hand, do not change their length during muscle contraction. When I-bands are short, they make the Z-lines move closer together.

The H-Zone is a tiny bit more complicated than the A-band, but the A-band has an even greater variety of acts. Unlike the H-Zone, the A-band is a spherical ring with actin and myosin filaments extending outward from each end.