MUSCLE PHYSIOLOGY

Detailed explanation-1: -The I bands contain only thin (actin) filaments, whereas the A bands contain thick (myosin) filaments. The myosin and actin filaments overlap in peripheral regions of the A band, whereas a middle region (called the H zone) contains only myosin.

Detailed explanation-2: -Two threadlike strands of filamentous actin twist together to make an actin filament, also known as a microfilament. Actin-binding proteins are important for the function of actin inside cells. Some actin-binding proteins promote actin bundling which can provide support or change the shape of cells.

Detailed explanation-3: -A sarcomere is composed of two main protein filaments (thin actin and thick myosin filaments) which are the active structures responsible for muscular contraction.

Detailed explanation-4: -A filament of actin is formed by two strands of F actin coiled about each other to form a double helical structure; it resembles two strands of pearls wound around each other and may be referred to as a coiled coil (Figure 2-8, C).