The role of calcium in muscle contraction is

A

To break the cross bridges as a cofactor in the hydrolysis of ATP

B

To bind with troponin, changing its shape so that the actin filament is exposed

C

To transmit the action potential across the neuromuscular junction

D

To re-establish the polarization of the plasmas membrane following an action potential

The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.So, the correct option is 'to bind with troponin, changing its shape so that the actin filament is exposed'.