Now, we have inside the cell is the cytosol. Outside the cell is the extracellular liquid, the fluid, which is also polar. So these heads of the phospholipids are polar, so they're hydrophilic, they will point outward. These heads are polar, they will point inward. And these hydrophobic tails, nonpolar tails, will basically aggregate in the middle. So this section here is known as the intermembrane space, the section between the outside and our inside.