In almost every Star Trek series or film,the main cast is usually made up of the officers who serve on the bridge. Whether it's on any of the Enterprises (seize your pick), the Defiant, or Voyager,or Ops on Deep Space Nine, you've usually got each member of the opening credits snug as their station, or with a Chief Engineer in Engineering,a Chief Medical Officer in sickbay, and perhaps a Quark tending bar.
Source: blastr.com