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MCAT Question A Day - 4/20/14 - Answer!

Curare is a chemical used in arrow poisons as well as in pharmaceutical compounds. It competes with acetylcholine for receptor sites along the motor end plate. The immediate physiological effects of high doses of curare can include

A.  decreased ability to relax muscles.
B.  inability to contract muscles and paralysis.
C.  inability to repolarize muscles.
D.  abnormal heat production in the affected muscle cells.

The correct answer is (B). General knowledge of neuromuscular relationships is needed. If curare competes with acetylcholine along the motor end plate (at the neuromuscular junction), ACh cannot perform its function. ACh normally causes skeletal muscles to depolarize and contract. If this is blocked, choice (B) is clearly the correct answer. Choices (A) and (C) refer to events after depolarization has already taken place. Heat production results from contraction (muscle activity), which requires ACh in the first place.

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