Smooth muscle contraction is slow and prolonged

Contraction of smooth muscle is significantly slower than that of skeletal muscle. Furthermore, smooth muscle contraction is quite prolonged (3000 msec) compared to that in skeletal muscle (100 msec). The slow onset of contraction as well as its sustained nature is due to the slowness of attachment and detachment of the myosin crossbridges with the actin. Two factors are involved  

In smooth muscle, myosin crossbridges have less myosin ATPase activity than those of skeletal muscle. As a result, the splitting of ATP that provides energy to prime the crossbridges, preparing them to interact with actin, is markedly reduced. Consequently, the rates of crossbridge cycling and tension development are slower. Furthermore, a slower rate of calcium removal causes the muscle to relax more slowly. 

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Explain why smooth muscle contraction is slow and prolonged... 

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