This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Charecteristic of smooth muscle cells in intestineMarch 2005 
Select and explain. 
A. Does not have actin and myosin, B. Cannot do sustained contraction, C. It contracts when stretched in the absence of any extrinsic innervation, D. Does not require calcium for contraction
C: It contracts when stretched in the absence of any extrinsic innervation
Answer: C: It contracts when stretched in the absence of any extrinsic innervation 
Explanation: Ans. C: It contracts when stretched in the absence of any extrinsic innervationUnitary smooth muscle (as present in a walls of a hollow viscus) is characterized by the instability of its membrane potential and by the fact that it shows continuous, irregular contractions that are independent of its nerve supply. This maintained state of contraction is called tonus/ toneIt does have actin and myosin-II but they are not arranged in regular arrays to give striations as in skeletal and cardiac muscle.They require calcium for initiation of contraction like skeletal and cardiac muscle.