Table of Organization of an Emergency Department?

[penta]

OK, this is an odd question, but worth asking.

For the same universe as my last post: My character's mom, ICly, I have decided is some sort of ER person. Not sure if Nurse or Doctor just yet. (Dad is a cop who just made it onto the SWAT team.)

To help me decide, I'm looking for position descriptions (and how many there are at each position, particularly per-shift....Also, how many shifts are there per day in an ER usually?) for the Emergency Department of a major metro area hospital - ICly, the character's from Boston, so I figure one of the major trauma centers up there like Mass General, but I'll take source info from anywhere in the US.

Sources searched:

Google (though I'm not sure how to structure the query)
Wikipedia (looking through links from the ER article)