What are the various stimuli to which our body reacts by initiating a yawn?

Asked by somyap | 24th May, 2010, 10:45: AM

Expert Answer:

It is not exactly known why people, or animals for that matter, yawn. It’s widely assumed that yawning occurs because we are tired, sleepy or bored or sitting in a stuffy room or because we see someone else doing it, but there isn’t any hard evidence to support these beliefs.

One of the explanation given is that we yawn because oxygen levels in our lungs are low. Studies have shown that during normal, at-rest breathing (or when we are bored or tired) we don’t use anywhere near our lung capacity; for the most part, we just use the air sacs at the bottom of the lungs. If the air sacs, called alveoli, don’t get fresh air, they partially collapse and the lungs stiffen a bit. Also carbon dioxide builds up in the blood. As a result, it’s believed, our brain prompts the body to either sigh or take a yawn to get more air into the lungs.



Yet another theory suggests that perhaps yawning is like stretching. Yawning and stretching increase blood pressure and heart rate and also flex muscles and joints.

Answered by  | 25th May, 2010, 07:12: AM

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