You are a scientist performing an experiment on some isolated skeletal muscle fibers. You observe that when you observe the muscle fibers under a microscope and apply a small amount of calcium, the fibers contract, but then after a short time they relax back to their original length. Which of the following is (are) possible explanation(s) for this observation? A) The applied Ca²⁺ activates the muscle, but following the refractory period the Ca²⁺ loses its effect and the muscle relaxes. B) The applied Ca²⁺ activates the muscle, but the muscle soon dephosphorylates its myosin and relaxes. C) The applied Ca²⁺ at first activates the muscle, but then is pumped into the sarcoplasmic reticulum and is stored. D) All of the choices are possible.

Question

Quizplus · Accepted Answer

Calcium initially causes muscle contraction by binding to troponin, but is then actively pumped back into the sarcoplasmic reticulum, leading to muscle relaxation.

You Are a Scientist Performing an Experiment on Some Isolated