MCAT Question A Day - 3/25/14 - Answer!

Rigor mortis, a condition in which skeletal muscles temporarily remain in a rigid state of partial contraction due to the absence of ATP, occurs a few hours after death. Which of the following steps is not necessary for muscle relaxation?

A. Repolarization of the sarcolemma

B. The return of calcium to the sarcoplasmic reticulum

C. The detachment of the troponintropomyosin complex from actin

D. The decomposition of acetylcholine by cholinesterase

The correct answer is (C). A basic understanding of the events involved with muscle contraction is required. Choices (A), (B), and (D) are all necessary for a muscle cell to return to its resting state. The troponin–tropomyosin complex must return to its original position on the actin (the position it occupied before calcium was released from the sarcoplasmic reticulum). When the complex detaches, muscle contraction occurs.

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