MICROANATOMY

Detailed explanation-1: -Smooth muscle cell contraction squeezes the cell from every direction since the myofibrils are not arranged in a pattern as in other muscles. Hence, light and dark bands are absent in smooth muscles.

Detailed explanation-2: -The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. Hence called striped muscles due to the presence of striations. Hence Myofibrils show dark and light bands in Cardiac muscles and striped muscles.

Detailed explanation-3: -The regular organization of myofibrils into sarcomeres gives cardiac muscle cells a striped or striated appearance when looked at through a microscope, similar to skeletal muscle. These striations are caused by lighter I bands composed mainly of actin, and darker A bands composed mainly of myosin.

Detailed explanation-4: -Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (bands or stripes).

Detailed explanation-5: -The light bands are called I bands and contain only thin filaments. The dark bands are called A bands and contain thick and thin filaments, with the thick filaments running the entire length of the A band. Thus the length of the thick filament determines the length of the A band.