So we have the cell membrane, this is our nucleus, the nuclear envelope that contains those nuclear pores, as well as our DNA that is found inside the nucleus. And this is our region known as the nucleolus. Now let's move on to region number four and region number five. Together, these two regions are known as the endoplasmic reticulum. Now, just outside the nucleus are a series of mazelike membranes called the endoplasmic reticulum, or simply the Er. And we have two types.