Answer:
Calcium is an essential ion as it required in the contraction of both cardiac and skeletal muscles. The sarcoplasmic reticulum stores these ions that are pumped by calcium pumps and released when contraction and functioning of these muscles. It binds to troponin and altered the change of shape and prevents tropomyosin from the site of the binding.
In case of cardiac muscle, the coupling Ca2+ is from its contact with extracellular concentration of Ca2+. When the calcium is released in the skeletal muscle it leads to the interaction between the actin and myosin. The binding sites of the myosin is exposed that bind and forms cross bridges with actin and hence helps in the contraction of the muscle. With the calcium induced calcium release, it helps in the contraction of the cardiac muscle. As the calcium is released it leads to initiation of the smooth muscle contraction in the cardiac muscle through binding of calmodulin and leads to activation of the myosin light chain kinase enzyme. There are receptors for the Calcium induced calcium release within the cardiac cells called as cardiomyocyte that binds to the calcium during depolarization and hence releases more calcium ions within the cells.