|MadSci Network: Neuroscience|
I do know that when a room builds up in carbon dioxide, a lot of people in the room, the carbon dioxide causes you to become sleepy and you begin to yawn even if you are not tired. It would seem to me that yawning is the streching of the neck and head muscles in order for the veins to constrict and move blood more rapidly to the brain. So hypoxia of the brain or carbon dioxide would trigger it. For further information, study about the veins and how blood is transported through them. John M. Lewis Mad Scientists
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