Smooth muscles are located around hollow organs such as blood vessels, digestive tract, urinary bladder, urogenital tract, airways. They play very important roles as effectors in homeostasis e.g. regulation of blood pressure via modulating total peripheral resistance; regulation of airflow through the airways. Smooth muscle contractile machinery, the mechanism of contraction and its regulation are more complicated than those of skeletal muscle. This allows for finer control of smooth muscle to fit its varied functions and circumstances. Structurally, smooth muscle is an involuntary muscle that lacks striations, sarcomeres, T-tubules, and troponin. Contraction is of “cockscrew” fashion instead of direct shortening seen in skeletal muscle.