MUSCLE PHYSIOLOGY

Detailed explanation-1: -The light bands are called I bands and contain only thin filament s. 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.

Detailed explanation-2: -In physiology, isotropic bands (better known as I bands) are the lighter bands of skeletal muscle cells (a.k.a. muscle fibers). Isotropic bands contain only actin-containing thin filaments. The darker bands are called anisotropic bands (A bands).

Detailed explanation-3: -Alone, thin filaments form light bands, called I bands, and are made from actin. The spacing between Z-lines decreases and the width of the H and I-bands decreases also during muscle contraction. The unit of muscle contraction is delimited by two Z-lines and is called the sarcomere.