4? I count 8.
Anyway, to know anything about the nodes, you'd have to know how they work. i.e. you'd have to make something up. And once you've started making stuff up, there's no better next step than to continue to do so. And so on. You think Volition consulted the Great Book of Immutable Science Fiction Truth before they went ahead? No. They winged it, and it worked. We wing it, and it works. Some people wing it, and they suck at it, and it shows, but asking someone else about it really won't get you any more information than you have at hand already, generally speaking. It's fiction, and thus imaginary to a large degree. The imagination it comes from is largely irrelvant.