In a relaxed muscle, the myosin heads of the sarcomeres' thick filaments are extended and ready to bind to the actin strands of the thin filaments. But this binding does not occur until an action potential is triggered in the muscle cell. An action potential results in the release of Ca2+ ions from the sarcoplasmic reticulum into the cytosol of the muscle cell.

As the concentration of Ca2+ rises in the cytosol, so does the concentration of Ca2+ in the sarcomeres. In response to changes in the Ca2+ concentration in the sarcomeres, two protein components of the thin filaments, troponin and tropomyosin, control access to actin's myosin-binding sites. In this way, Ca2+ concentration in the cytosol and sarcomeres regulates muscle contraction.

Which of the following statements correctly describe(s) the relationship between Ca2+ concentration in the cytosol and the response in the sarcomere? Select all that apply.

A. Decreasing Ca2+ concentration promotes interactions between actin and myosin.

B. Increasing Ca2+ concentration causes troponin to bind to tropomyosin.

C. Decreasing Ca2+ concentration causes dissociation of Ca2+ from troponin.

D. Increasing Ca2+ concentration causes movement of tropomyosin, exposing myosin-binding sites on actin.

E. Increasing Ca2+ concentration causes troponin and tropomyosin to bind to actin.