What are muscle filaments?
the myofibrils in muscle fibers are Actin and Myosin. The two of them slightly over lap while the muscle is resting, when the muscle contracts, after a series of reactions that supply myosin with ATP and Calcium exposes certain receptors on Actin, the Myosin repeatedly attaches small little golf club like heads to the Act in order to pull its self in closer to overlap with the Act even further (this is the contraction). These myofibrils overlap in alternating order creating the functional unit of a muscle fiber called a Sarcomere.
