In the “energizing stage” of the sliding filament theory of muscle contraction, atp breaks down and releases energy to cause the myosin head to tilt about 45 degrees. describe what happens stages occur next. theorize what might happen if there were not atp present.

Calcium ions presents Ca+ binds to troponin which makes tropomyosin move out of way for myosin to attach. Cross-bridge attaches. ATP breakdown provides energy to ready the myosin head for a power stroke. Myosin head attaches to exposed binding site on actin and the power stroke is accomplished. Cross-bridge (Myosin head) springs from raised position and pulls on the actin filament. Cross bridges break, ATP binds to Cross-bridge (but is not yet broken down) Myosin heads are released from actin. As long as calcium ions and ATP are present, this walking continues until the musle fiber is fully contracted. Hope this helps!