9 s Figure 9.3: Cross Bridge Cycle View Available Hint(s) ATP actin binding sites blocked energized/cocked myosin head extracellular fluid Submit cytoplasm ADP and Pi low-energy myosin head actin-binding sites exposed 1. Location of higher concentration of Ca+ needed for cross bridge formation and cycling: 2. Actin status to begin cross bridge formation: 3. Molecule(s) bound to the myosin head at the start of the cross bridge cycle: 4. Energy state of myosin for beginning cross bridge formation: Reset Help The Power Stroke When the bond between myosin and actin forms, ADP and Pi are released. In the power, or working, stroke, the release of ADP and Pi triggers the myosin head to pivot into its low-energy conformation as the myosin neck extends. Since the two filaments are still bound, the movement of the myosin head causes the actin filament to be pulled along with it. This action ratchets the actin myofilaments toward the M line, changing the lateral boundaries of the sarcomere (i.e., the Z discs