Physiology of Muscle Contraction

Muscle contraction occurs when signals from the nervous system trigger muscle fibers to slide their tiny protein filaments—called actin and myosin—past each other. This process requires energy from ATP and involves the release of calcium ions, which enable myosin to attach to actin. When myosin pulls on actin, the muscle shortens or contracts. This coordinated action across many fibers results in movement or force. Once the signal stops, calcium levels decrease, and the muscle fibers return to their relaxed state, ending the contraction.