The process of muscle contraction involves a series of biochemical and mechanical events. It starts with an electrical impulse from the nervous system that triggers an action potential in the muscle cell membrane. This action potential travels along the sarcolemma and into the muscle fiber via the transverse tubules. This leads to the release of calcium ions from the sarcoplasmic reticulum into the cytoplasm of the muscle cell.
Calcium ions bind to the protein troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on the actin filaments. This allows the myosin heads to attach to the actin filaments, forming cross-bridges. The myosin heads then pivot, pulling the actin filaments toward the center of the sarcomere, which shortens the muscle fiber. This process is powered by ATP, which is hydrolyzed by the enzyme myosin ATPase.
