The calcium ions are attached with the troponin which helps in the action of actin and myosin.
Step-by-step explanation:
Actin and myosin are the two proteins that are associated with the function of muscle i.e contraction and relaxation. The contraction of muscles are associated with the actions of sliding movements of these proteins. But before the impulse is recieved by the muscle cell, the actin filaments remain inactivated by the troponin which block the active sites of troponin. As the impulse is recieved by the muscle cell, the calcium is released by the sarcoplasmic reticulum which then combines with the troponin of the actin molecules and the rest of the contraction process can progress further to achieve contraction.