Begin by considering a relaxed muscle. in this state, the myosin molecules of the thick filaments are not in contact with the actin of the thin filaments, and adp and pi are bound to the myosin heads. an action potential on the muscle cell plasma membrane initiates contraction of the sarcomeres from this relaxed state.

Three different types of muscles are cardiac muscle, smooth muscle and skeletal muscle. The movement of muscle require the protein like actin, myosin and troponin.

The contraction and relaxation of muscle occurs in the sequential events.The cross bridge formation occurs by the myosin head with actin. The inorganic phosphate is released by myosin. The actin is pulled by myosin towards the sarcomere center. The binding of ATP with myosin occurs. The actin and myosin cross bridge breaks and the hydrolysis of ATP occurs by myosin. Finally, the extension of myosin heads.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.