Interesting!
I've never considered it being anything other than a 'brain rocking / concussion' thing.
So my understanding is that if a fighter has a 'weak chin' this sort of means he has a 'weak neck' that cannot stop his head from rocking this way or that to 'absorb' the force of a punch....leading his head/brain to rock instead aka knockout.
I was never good at biology! When you say 'nervous system rather than respiratory', what do you mean?
What I meant is that I think it's the brain banging against the skull rather than it losing oxygen, so closer to your idea than your friends. You're right about the 'weak chin' though.
There's different types of KO though and I don't know if they're all caused by the same thing. Sometimes the lights go out and they go to sleep, like Pacquiao when he got KOd by JMM. Then you get the chicken dance where they're awake but the legs have gone from under them. And you get the ones on the ear where they lose balance, like Price the first time he got KOd.
Not to mention KOs to the body which probably are respiratory most of the time.
