Calcium is important in skeletal muscle contraction because it
• Signal for contraction increase Ca++ level many folds in the sarcoplasm.
• Ca++ now binds with sub-unit of troponin (troponin "C") which is masking the active site on actin filament and displaces the sub-unit of troponin.
• Once the active site is exposed, head of the myosin attaches and initiate contraction by sliding the actin over myosin.