Is there any possibility that it has to do at least in part with physical/mechanical fluid flows, in addition to cell-level activity? I remember reading about h

Is there any possibility that it has to do at least in part with physical/mechanical fluid flows, in addition to cell-level activity? I remember reading about how we are discovering complicated fluid systems within the brain, and we already know about things like the lymphatic system. I also wonder about yawning as a kind of "stretching" for the head/neck muscles, respiratory system, mouth, and brain. And general about the purpose of stretching as a way to somehow reset, awaken, or moderate nerve connections between the brain and various parts of the body.