I think it's worth mentioning (although probably ultimately not relevant to Dr. McCoy's Laboratory set), that when we see the lab panel in "Dagger of the Mind," "The Menagerie, Part 1," and "The Alternative Factor," it had a "microphone" extension.
This "microphone" (at least it was used as a microphone in "Dagger...;" who knows what its function was in its other two appearances) was actually a high-intensity lamp that was built into a telescoping antenna for an old Westinghouse radio/lamp combination. The base part of the device was used as a "recorder" in a number of episodes--starting with "The Man Trap." The telescoping light was removed and salvaged, and used as part of the above three sets. Once the panel became part of the lab, this microphone-deal was removed altogether, being replaced with a simple red "ice cube" indicator--which is funny, because that's pretty much what they did to the prop from which it was originally removed.
Here's a "before and after" picture: