I subscribe to the Voiceovers group on the Yahoo newsgroups and this link came during a discussion on care for the voice. If you have never seen your vocal folds in action, then you might want to check this page out. While it is aimed at singers, voiceover folk use the same equipment.
http://web.me.com/bdietzler1701/Mr._Dietzlers_MusicPage/VocalCords.html
And then scroll down the page a bit and see how the diaphragm works.
This is by far my favorite site about vocal health:
http://www.uiowa.edu/~shcvoice/index.html
It’s a self-directed virtual school for the vocal health of US teachers….. well, for any professional speaker, really.