Muscle Contraction · Histology

During muscle relaxation, how are calcium levels in the sarcoplasm reduced?

  1. Calcium diffuses out of the cell into the extracellular fluid.
  2. Calcium is neutralized by phosphate ions.
  3. Calcium is returned to the sarcoplasmic reticulum by SERCA.
  4. Calcium is broken down by cytoplasmic enzymes.
Show answer and explanation

Correct answer: Calcium is returned to the sarcoplasmic reticulum by SERCA.

The SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase) pump uses ATP to move calcium against its concentration gradient back into the SR. This drop in cytoplasmic calcium causes it to dissociate from troponin.

Difficulty: Medium Question 12 of 19

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