Excitation Contraction Coupling
The arrival of an Action Potential at Sarcoplasmic Reticulum causes release of Ca2+ down the concentration gradient to sarcoplasmic reticulum. Released Ca2+ causes conformational changes to effect contraction. As action potential passes, Ca2+ are pumped again to sarcoplasmic reticulum and relaxation happens. This cycle is known as Excitation Contraction Coupling.