This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
The site where myosin heads to action in skeletal muscles are covered by 
Select and explain. 
A. Tropomyosin, B. Troponin o, C. Calcium, D. None of the above
A: Tropomyosin
Answer: A: Tropomyosin 
Explanation: In resting muscle, troponin I is bound to actin and tropomyosin covers the site where myosin head interacts with actin. Ref: Ganong&;s Review of medical physiology;25th edition; pg: 104.