The interaction between which protein and ion initiates contraction of skeletal muscle?

Calcium ions attach to calmodulin which then activate protein kinase. This occurs in the neuromuscular junction, specifically in the synaptic cleft, which is the space between the axon bulb and the sarcolemma. The protein kinase allows the fusion of synaptic vesicles. Acetylcholine reaches the muscle fibers and activates Sodium ions which innervate the muscles.

Giga is the second highest prefix on the normal scale, the first is terra.