This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscle, Subject name: Physiology
[{'content': 'The coupling agent between electrical excitation and contraction of a muscle is said to be: \nSelect and explain. \nA. Dihydropyridine receptor (DHPR), B. Ryanodine receptor, C. Ca++, D. Troponin C', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Coupling: electrical excitation travels into muscle, releases calcium & this calcium combines with troponin & causes muscle contraction. Events tills the release of calcium is electrical & after that is mechanical. T tubules contain DHPR & L tubules contain RYR.', 'role': 'assistant'}]