This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Contractility of cardiac muscle depends on \nSelect and explain. \nA. On T tubules, B. On T tubules and extracellular Ca2+, C. On extracellular Ca2+, D. On intracellular Ca2+', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Excitation and contraction coupling is there in cardiac muscle. When an action potential reaches the T tubules there is activation of Dihydropyridine channels. This causes influx of extracellular calcium into sarcoplasm. Ref: Textbook of medical physiology by N Geetha, 2nd edition, page no. 53', 'role': 'assistant'}]