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MCAT Question A Day - 4/27/14 - Answer!

If a muscle cell is stimulated a second time before it has time to relax completely, a stronger contraction results. What is this phenomenon called?

A.  Tetany
B.  Partial (incomplete) tetany
C.  Summation
D.  Threshold stimulation

The correct answer is (C). Knowledge of basic concepts in muscle physiology is helpful. Since the described phenomenon involves only a second contraction, summation is the appropriate answer. If the situation involved multiple stimuli (20–30) in rapid succession, partial tetany would be correct. Tetany occurs when multiple stimuli occur so rapidly that there is no time to relax at all. Threshold refers to the level of stimulation required to initiate any response by the muscle cell.

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