I think nodding is naturally connected to accepting because you're somehow putting your head below the other person in front of you. And being down is connected to less power, up for more power, more energy, as laws of gravity say. The Wolf that is up is the powerful one, because he has gravity on his side.
As for the case of "no" it seems that comes as a contrast to the previous explanation, a counterpart to nodding. You're deviating your face from the person in front of you like directing it towards other people or places, meaning that you agree with other realities, not the one expressed by that person. Or creating some kind of barrier of air before him/her.