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Contraction cycle of muscle fibers

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Cycle begins:
1. After the Ca + + binds to troponin, the moves and frees the myosin binding site. Myosin then binds to that site on actin.
2. The binding of ATP decreases the affinity of myosin to actin and release
3. The cebeza of myosin with bound ATP undergoes a hidrlisis ATP to ADP and that changes the protein conformation swerving back.
4. The binding of ADP increases the affinity of myosin for actin and bind.
5. The output of ADP from the myosin creates a conformational movement forward, pulling the actin fiber.
6. This cycle is repeated, making in each cycle the myosin head is attached to post sites to advance successive actin fiber.

In conclusion
1. To get a muscle is required Ca + + and ATP
2. This cycle is repeated many times to produce a muscle contraction
3. Muscle relaxation is caused by lack of calcium, blocking the myosin binding site and the impossibility of that happening this cycle until it reaches a new signal.
4. The cramps are due to the lack of oxygen and the consequent lack of ATP (cellular respiration) in the cell. In the absence ATP, myosin has difficulty letting go of the actin and the muscle tends to remain contracted.