Final answer:
Each myosin head has binding sites for both actin and ATP, enabling the myosin to attach to actin for muscle contraction and then detach when ATP is bound and hydrolyzed.
Step-by-step explanation:
The question asks which substances each myosin head has a binding site for. Based on the information provided, we understand that a part of the myosin head has a binding site for actin, which allows it to form a cross-bridge during muscle contraction. Furthermore, the myosin head also binds to ATP, which is essential for the detachment of the myosin head from actin and for providing the energy needed for the subsequent power stroke. Therefore, the correct answer to the question is E) actin and ATP. It's worth noting that calcium ions do bind to troponin, which leads to the exposure of the binding sites on actin; however, calcium does not bind directly to the myosin head.