[yebyen]

Ayn is a voiced pharyngeal fricative, ghayn is a voiced velar fricative. My intuitive answer was wrong, I thought the difference was one is fricative and the other is not... at any rate, those are points of articulation, not muscles.

An articulation point is simply supposed to be the place where you put your tongue. In this case it's so far back in your throat, I'm not sure you actually can put your tongue there.

But the muscles are in your tongue, the articulation points are just places in your mouth. Like the palate, for palatal consonants, or lips for labial, in some more familiar examples.