And because of the existence of this electrochemical gradient, the calcium ions can quickly and effectively move into the cytoplasm where they are needed to basically contract that muscle. So let's take a look at the following diagram. This is basically the generalization of how the ptype ATPases actually work. 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.