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It is a signal, caused by an involuntary reflex, that the body needs sleep. Once yawning starts, it’s nearly impossible to stop. The person may close the mouth, but the muscles triggered by the reflex continue to contract. Humans and many other animals yawn when oxygen starts to run low in their environment and when their muscles are completely relaxed. A person who yawns frequently is probably not getting enough oxygen for their needs. She may need a more ventilated environment or exercise. In general, such a person will stop yawning if he drinks something or bathes his face in cold water.
“Yawning is still not well known in medicine”, says Arnaldo Lichtenstein, a general practitioner at the Hospital das Clínicas in São Paulo. It remains to be clarified which part of the nervous system controls the reflex, possibly the midbrain (in the center of the brain). One purpose of yawning may be to wake you up by stretching your muscles and helping your blood flow.
“There are many people who believe that it is very useful in our day-to-day lives. When a person is drowsy, the distension of the pulmonary alveoli is a little smaller and yawning, as well as sighing, would then serve to undo these small lung collapses”, says Arnaldo.
The reflex can also be triggered by the sight of another yawn – that is, it is contagious: when we see someone yawning, we immediately feel like doing the same.
Yawning opens the airways to give more oxygen to the body
1. The contraction of the pulmonary alveoli is one of the reactions that trigger the yawning reflex
2. The brain triggers this reflex by making the muscles in the face twitch and the mouth open, increasing the intake of air.