MCAT Question A Day - 7/15/13 - Answer!
What would be the expected result if cholinesterase were not released at the neuromuscular junction?
A. The muscle would fully contract and relax once.
B. The muscle would relax only.
C. The muscle would continue to contract without being able to relax normally.
D. The muscle would fully contract and relax repeatedly.
The correct answer is (C). Cholinesterase is released at the neuromuscular junction in order to break down acetylcholine and prevent this neurotransmitter from restimulating the muscle cell. The enzyme thus allows the muscle cell to relax. If ACh were not broken down, it would continue to allow Na+ ions across the sarcolemma, and repolarization would not be possible.
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