ANATOMY

Detailed explanation-1: -Muscle contraction is brought about by sliding movement of actin filaments over myosin filaments. When a muscle fibril contracts, it’s A band remains constant and I band shortens. H – Zone disappears.

Detailed explanation-2: -During muscle contraction, the I band reduces in size as the overlap between the thick filaments and the thin filaments increases. The H zone also decreases in length because of the same reason.

Detailed explanation-3: -As the ends of the actin filaments get closer to the M band, the I band appears denser and the H zone becomes narrower.

Detailed explanation-4: -The H zone-the central region of the A zone-contains only thick filaments (myosin) and is shortened during contraction. The H zone becomes smaller and smaller due to the increasing overlap of actin and myosin filaments, and the muscle shortens. Thus when the muscle is fully contracted, the H zone is no longer visible.

Detailed explanation-5: -H zone. Definition: The H zone is in the center of the A band where there is no overlap between the thick and the thin filaments. Therefore, in the H zone, the filaments consist only of the thick filament. The H zone becomes smaller as the muscle contracts and the sarcomere shortens.