This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
The latch-bridge mechanism in smooth muscle is responsible for: 
Select and explain. 
A. Fast muscle twitch, B. Sustained muscle contraction, C. Excitation-contraction coupling, D. Unstable membrane potential
B: Sustained muscle contraction
Answer: B: Sustained muscle contraction 
Explanation: Ans. B. Sustained muscle contractionThe twitch duration in sphincters and smooth muscle is particularly longer. Latch bridges are actomyosin complexes that detach slowly; this is made possible by a slow myosin ATPase. In turn, this enables maintenance of tension for longer periods without consumption of more ATP.