MUSCLE PHYSIOLOGY

Detailed explanation-1: -For a muscle cell to contract, the sarcomere must shorten. However, thick and thin filaments-the components of sarcomeres-do not shorten. Instead, they slide by one another, causing the sarcomere to shorten while the filaments remain the same length.

Detailed explanation-2: -During muscular contraction, the myosin heads pull the actin filaments toward one another resulting in a shortened sarcomere. While the I band and H zone will disappear or shorten, the A band length will remain unchanged.

Detailed explanation-3: -Contractions that involve shortening of the muscle are referred to as isotonic or concentric contractions. This type of contraction occurs when the force generated by the muscle is greater than the constant load acting on the muscle.

Detailed explanation-4: -Once the myosin-binding sites are exposed, and if sufficient ATP is present, myosin binds to actin to begin cross-bridge cycling. Then the sarcomere shortens and the muscle contracts.