GENERAL HISTOLOGY

Detailed explanation-1: –The dark band is known as ‘A’ or Anisotropic band which carries Myosin whereas the light bands which carry actin and are called I-band or Isotropic band. Hence called striped muscles thanks to the presence of striations.-Hence Myofibrils show dark and lightweight bands in Cardiac muscles and striated muscles.

Detailed explanation-2: -Myofibrils are composed of overlapping thick and thin myofilaments organized into distinct, repeating units called sarcomeres.

Detailed explanation-3: -Z-lines mark the boundaries of the sarcomeres. The dark staining region in the centre of the sarcomere is called the A (anisotropic) band. The lighter staining band, through which the Z-line passes is called the I (isotropic) band. A diagram of a muscle sarcomere is shown below.

Detailed explanation-4: -The myofibrils have alternating bands that appear lighter and darker, which gives them a striped appearance. These bands are due to the two protein myofilaments called actin and myosin. As actin is a thin filament, made up of two strands twisted around each other, it has a lighter appearance.