And during contraction, calcium flows into the cytoplasm of the cell from the sarcoplas reticulum lumen down into its concentration, down its concentration gradient. And once the contraction is over, to actually relax that muscle, these calcium ions must be sequestered back into the lumen of the sarcoplas reticulum. And this is done by these pumps because this actually requires energy to move these calcium ions against their electrochemical gradient. And this is exactly where the calcium Atpas actually comes into play. Calcium Atpas uses ATP molecules to move these calcium ions against the electrochemical gradient. And calcium Atpas is also sometimes called circa, where the S and E stands for sarcoplas reticulum, slash, endoplasm, reticulum.