So let's begin with the general diagram. And then let's look at the specifics. So, this is the lumen of the sarcoplasma ticulum, this is the membrane of the sarcoplasmarticulum and this is the cytoplasm of the muscle cell. So we have a high concentration on the lumen side, a low concentration of calcium on the cytoplasmic side. So this is our ptype Atpas. In this case it's the calcium Atpas.