Step-by-step explanation:
I haven't learned about this yet but this is what I found online-
"What is the role of calcium in muscle contraction? Ca ions and proteins bond to actin play a crucial role in both muscle cell contraction and relaxation. ... It binds to the troponin complex, causing tropomyosin bound along the actin strands to shift position and expose the myosin binding sites on the thin filament."
I hope this can help a bit