@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