36. What is the role of calcium in muscle contractions?
(A) to break the cross-bridges as a cofactor in the hydrolysis of ATP
(B)to spread the action potential through the T-tubules
(C)to transmit the action potential across the neuromuscular junction
(D)to bind with troponin, changing its shape so that binding sites on the actin filament are exposed
(E) to re-establish the polarization of the plasma's membrane following an action potential