Describe the process of muscle contraction and relaxation

Describe the process of muscle contraction and relaxation in detail, including the role of calcium ions, ATP, and the sliding filament theory. Begin by explaining how a nerve impulse triggers muscle contraction at the neuromuscular junction, leading to the release of calcium ions from the sarcoplasmic reticulum. Then, elaborate on how calcium ions bind to troponin, causing tropomyosin to move aside and expose the myosin-binding sites on actin. Subsequently, delve into the mechanism of cross-bridge formation between myosin and actin, powered by ATP hydrolysis, leading to the sliding of filaments and muscle contraction. Finally, discuss the role of ATP in detaching the myosin heads from actin during muscle relaxation, as well as the active transport of calcium ions back into the sarcoplasmic reticulum, restoring the muscle’s resting state.