Myosin III is a poorly understood member of the myosin family. ATP causes the binding between actin and myosin filaments to break. ATP binds to the cross bridges between myosin heads and actin filaments. The calcium drives the movement of myosin and actin filaments. The filaments of actin and myosin then form linkages. Myofilaments are the filaments of myofibrils, constructed from proteins, principally myosin or actin. The interaction of myosin and actin is responsible for muscle contraction. Dynein complexes are much larger and more complex than kinesin and myosin motors. These proteins are associated with actin and cooperate to prevent its interaction with myosin. These are mostly associated with muscle contraction, and bind with actin, myosin, tropomyosin, and troponin. Muscle fibers have myofibrils, which are able to contract due to actin and myosin. Muscles contract by sliding the thick (myosin) and thin (actin) filaments along each other. S1 fragments&colon; they themselves are subunits of the larger myosin II protein complex. The myosin and kinesin, respectively, are attached to the bottom of the network channels. Thick filaments are made of the elongated protein myosin.