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
[{'content': 'Sudden decrease in serum calcium is associated with: \nSelect and explain. \nA. Increased thyroxine and PTH secretion, B. Increased phosphate, C. Increased excitability of muscle and nerve, D. Cardiac conduction abnormalities', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Increased excitability of muscle and nerve.A decrease in extracellular Ca2+ concentration increases the excitability of nerve and muscle cellsQ by decreasing the amount of depolarization necessary to initiate the changes in Nat K+ conductance that produces the action potential. An increase in Ca2+ concentration stabilizes the membrane by decreasing the excitability.Decreasing the external Na+ concentration decreases the size of action potentialQ but has little effect on RMP.Increasing the external K+ concentration decreases the RMPQ.', 'role': 'assistant'}]