While the majority of the human population uses their muscles on a daily basis, few realize what a complicated process the body goes through simply to lift a finger. Each skeletal muscle is composed of many individual muscle cells, or muscle fibers.
Muscle fibers contain myofibrils, which in turn contain myofilaments.
These microscopic myofilaments are the unit that performs the actual contraction. The process of muscle excitation and contraction is extremely detailed. This causes the channels to open and allow sodium and potassium ions to diffuse, creating a change in polarity which in turn creates an action potential. The action potential stimulates the release of calcium. The calcium binds to the troponin on the thin filaments and causes the troponin to move, exposing a site for the myosin on the thick filaments to bind to the actin on the thin filaments.