@Mytran - excellent spotting that opaque ceiling in WNMHGB!
@Cary L. Brown - Even though Roddenberry might have intended it to be a windowed ceiling dome it doesn't appear to be that on screen in the interior shot. There does appear to be a small opening near the very center, so it could be some type of framework in the opaque ceiling that just happens to be covered up by ceiling panels as per your suggestion (ala TMP). The small opening could lead upward to some kind of glowy-light machinery that's part of the sensor dome above. I'll give that a go to model at some point when I make it up to the bridge
To be entirely fair... we never saw the ceiling of the bridge at all, did we? And what little portion of the "above the lighting cove" region we saw was simply black. And, of course, from a brightly lit room, most of the time all you'd be able to see would be blackness.
The only STRONG argument for an entirely enclosed ceiling would be "Balance of Terror," I suppose... but then again, if the nuke going off just a few hundred meters ahead of the Enterprise didn't blast it to vapor, obviously the shields blocked most of that. Still, you'd think that more radiation would go through a transparent dome than through hull material, as a rule...