Question

Which of the following does not occur when a sarcomere contracts?

a. the thin filaments are pulled toward the center of the sarcomere

b. the lengths of the thin and thick filaments are unchanged

c. the thin and thick filaments increasingly overlap

d. the distance between the ends of the sarcomeres (Z discs) increases

e. the width of the A band is unchanged

f. the H zone and I band become narrower

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Which of the following would not help a muscle cell to relax?

a. breakdown of acetylcholine by acetylcholinesterase

b. pumping calcium ions from the sarcoplasm into the sarcoplasmic reticulum

c. covering or blocking the myosin-binding sites

d. increasing the flow of sodium ions from the outside (interstitial fluid) to the inside of

     the sarcolemma

e. repolarization of the sarcolemma

Answer 1

Answer: distance between the ends of the sarcomeres (z discs) increases

Explanation:thin and thick filaments are present within the Z lines,when the contraction occurs in the sarcomere ,both end of z lines move towards the center of sarcomere,so distance between the z lines decrease.option d is incorrect whereas other options are correct in the sarcomere contractions.thick and thin filaments get overlap,thin filaments move towards the centre,width of A band is not changed.

Answer:(B) pumping calcium ions from the sarcoplasm to sarcoplasmic reticulum.

Explanation: normally calcium get released from the sarcoplasmic reticulum for the muscle contraction and it make interactions between the myosin and actin filaments get overlap.main function of calcium in muscle cell is contraction of muscles.so by this above process not helps in muscle relax.

Whereas other option are correct for the muscle relaxation.