The heads of myosin molecules contact the actin filaments when a muscle is relaxed. The heads of myosin molecules contact the actin filaments when a muscle is relaxed. True False

The above statement is "false".

Explanation:

The following events take place during contraction-relaxation of a muscle:

•Action potential in T tubule activates voltage-sensitive receptors,which in turn trigger Ca ions release from terminal cisternae of sacroplasmic reticulum(SR) into cystol.

•Ca ions bind to troponin;troponin changes shape,removing the blocking action of tropomyosin;actin active sites is exposed.

•CONTRACTION; myosin heads alternatively attach to actin and detach,pulling the actin filaments toward the center of the sarcomere;using ATP in this process.

•removal of Ca ions by active transport into the SR after the action potential ends.

•RELAXATION occurs.Actin and myosin return back to its unbound state.

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