The best way to visualize the pelvic diaphragm is to imagine you are peering down into it from the top. The pelvic cradle literally forms a bowl, and that bowl is lined with muscle, making the container we are calling the pelvic diaphragm. It’s like an upward facing bowl. Here are some pictures:

The shoulder diaphragm is less literal, but if you think about the tops of both of your lungs, those are like two little downward facing bowls. Now just imagine that entire expanse — the tops of the lungs and the area between them — as one big downward facing bowl.

The respiratory diaphragm is the only literal diaphragm in this system, and it flexes both ways. On the inhale, it pushes down into the abdomen to form a somewhat upward facing bowl, and on the exhale, it comes up to the lungs and forms a downward facing bowl.