Ans. D. Actina. In both smooth and striated muscle, contraction is produced by the cross- bridge cycle in which the cross-bridge on the thick filament binds to the actin molecule on the thin filament.b. In excitation-contraction coupling in striated muscle, calcium initiates contraction by binding to troponin.c. The calcium-activated troponin then acts to remove the tropomyosin-mediated inhibition of the actin-myosin interaction. In excitation-contraction coupling in smooth muscle, calcium initiates contraction by binding to calmodulin. The calcium-activated calmodulin then activates the myosin light chain protein kinase (MLCK) enzyme, which phosphorylates the myosin light chains. Actin-myosin interaction follows light-chain phosphorylation.