<prompt> True regarding excitation contraction coupling in smooth muscles isPresence of troponin is essentialSustained contraction occurs with high calcium concentrationPhosphorylation of actin is required for contractionPresence of cellular calcium is essential to cause muscle contraction  <response>: Troponin is needed for skeletal muscle contraction, not smooth muscle. Sustained contraction occurs due to latch. Myosin needs to be phosphorylated rather than actin for smooth muscle contraction. 