ANATOMY

Detailed explanation-1: -A thin filament of myofibril contains 2 ‘F’ actins and two other proteins, namely troponin and tropomyosin. Tropomyosin and troponin regulate muscle contraction. Troponin binds to the calcium ions and removes the tropomyosin from the actin myosin binding site which allows the muscle contraction.

Detailed explanation-2: -Thin filaments are composed primarily of the contractile protein actin. As illustrated in Figures 2-8, A and B, actin is composed of small globular subunits (G actin) that form long strands called fibrous actin (F actin).

Detailed explanation-3: -The myofibrils are made up of thick and thin myofilaments, which give the muscle its striped appearance. The thick filaments are composed strands of the protein myosin, and the thin filaments are strands of the protein actin, along with two other muscle regulatory proteins, tropomyosin and troponin.

Detailed explanation-4: -Most of the cytoplasm consists of myofibrils, which are cylindrical bundles of two types of filaments: thick filaments of myosin (about 15 nm in diameter) and thin filaments of actin (about 7 nm in diameter).