MUSCLE PHYSIOLOGY

Detailed explanation-1: -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-2: -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).

Detailed explanation-3: -In vertebrate striated muscles, the assembly of myosin molecules is arranged in such a way as to form bipolar filaments, with a central bare zone or M-region, where there are no myosin heads, corresponding to the centre of the sarcomere (Figure 5a).