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Why We Yawn

Rather than fatigue or boredom, researchers propose that yawning may cool an overheated brain.

By | November 17, 2011

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Publishing in the recently resurrected journal Medical Hypotheses, researchers from Yale University and the University of Maryland propose that yawning, which opens the sinuses located to the left and right of the nose, acts to cool the brain when it gets too hot.

Excessive yawning, argue the researchers, appears to be a symptom of conditions that increase the brain or core temperature, such as damage to the central nervous. In addition, fits of yawning often precede epileptic seizures and migraines. Therefore, the authors say, understanding the physiological purpose of the reflex could have medical relevance.

Earlier work by the authors showed that the brains of mice increased in temperature just before a yawn and decreased directly after. The authors propose that the mucus within the sinus constantly evaporates and, like a refrigerator, cools the surrounding blood vessels and cerebrospinal fluid. A yawn, they suggest, would amplify this process by stretching the jaw, which flexes the walls of the sinus bringing new air into it rapidly cooling an overheated brain.

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Comments

Avatar of: jhnycmltly

jhnycmltly

Posts: 65

November 17, 2011

One hypothesis is acidosis. Yawning causing a more alkaline environment. Yawning lowers the acidity of the body.

Avatar of: Paul

Paul

Posts: 1457

November 17, 2011

Evaporative cooling from the sinuses of many animals to help lower their body temperature is a known fact.  Dogs almost exclusively use evaporative heat transfer breathing in and out of their noses with an increased respiration rate just prior to switching over to panting when more evaporation is needed.  For humans, however, looking at the thermodynamics, I have a tough time swallowing this hypothesis under normal, non-pathologic circumstances.  With so much blood flow to the brain, any evaporative heat transfer cooling from one or two yawns would be very quickly countered by a convective reheating.  Yes, the brain may be cooled ever so slightly, but that is not the reason for yawning.

Here is another example where researchers inappropriately try to directly translate research from certain animals to humans.  Humans sweat...mice don't.

Avatar of: Helen J Gardiner

Helen J Gardiner

Posts: 1

November 17, 2011

Its a very poorly understood phenomenon - I have always wanted to know what causes my own bouts of yawning as they don't seem to relate to the usually given  reasons such as tiredness or boredom. It will be interesting to see where this study goes.

Avatar of: sgall

sgall

Posts: 1

November 17, 2011

They are suggesting that the brain's temp rises causing the yawn.  I was wondering if the body knows the yawn is coming due to some other reason then warms the brain a little so that when yawning, the brain doesnt go below a certain temp.

Avatar of:

Posts: 0

November 17, 2011

One hypothesis is acidosis. Yawning causing a more alkaline environment. Yawning lowers the acidity of the body.

Avatar of:

Posts: 0

November 17, 2011

Evaporative cooling from the sinuses of many animals to help lower their body temperature is a known fact.  Dogs almost exclusively use evaporative heat transfer breathing in and out of their noses with an increased respiration rate just prior to switching over to panting when more evaporation is needed.  For humans, however, looking at the thermodynamics, I have a tough time swallowing this hypothesis under normal, non-pathologic circumstances.  With so much blood flow to the brain, any evaporative heat transfer cooling from one or two yawns would be very quickly countered by a convective reheating.  Yes, the brain may be cooled ever so slightly, but that is not the reason for yawning.

Here is another example where researchers inappropriately try to directly translate research from certain animals to humans.  Humans sweat...mice don't.

Avatar of:

Posts: 0

November 17, 2011

Its a very poorly understood phenomenon - I have always wanted to know what causes my own bouts of yawning as they don't seem to relate to the usually given  reasons such as tiredness or boredom. It will be interesting to see where this study goes.

Avatar of:

Posts: 0

November 17, 2011

They are suggesting that the brain's temp rises causing the yawn.  I was wondering if the body knows the yawn is coming due to some other reason then warms the brain a little so that when yawning, the brain doesnt go below a certain temp.

Avatar of:

Posts: 0

November 17, 2011

One hypothesis is acidosis. Yawning causing a more alkaline environment. Yawning lowers the acidity of the body.

Avatar of:

Posts: 0

November 17, 2011

Evaporative cooling from the sinuses of many animals to help lower their body temperature is a known fact.  Dogs almost exclusively use evaporative heat transfer breathing in and out of their noses with an increased respiration rate just prior to switching over to panting when more evaporation is needed.  For humans, however, looking at the thermodynamics, I have a tough time swallowing this hypothesis under normal, non-pathologic circumstances.  With so much blood flow to the brain, any evaporative heat transfer cooling from one or two yawns would be very quickly countered by a convective reheating.  Yes, the brain may be cooled ever so slightly, but that is not the reason for yawning.

Here is another example where researchers inappropriately try to directly translate research from certain animals to humans.  Humans sweat...mice don't.

Avatar of:

Posts: 0

November 17, 2011

Its a very poorly understood phenomenon - I have always wanted to know what causes my own bouts of yawning as they don't seem to relate to the usually given  reasons such as tiredness or boredom. It will be interesting to see where this study goes.

Avatar of:

Posts: 0

November 17, 2011

They are suggesting that the brain's temp rises causing the yawn.  I was wondering if the body knows the yawn is coming due to some other reason then warms the brain a little so that when yawning, the brain doesnt go below a certain temp.

Avatar of:

Posts: 0

December 7, 2011

Hmm.  I have fits of yawning whenever I work out with my athletic trainer.  It's always disconcerting because my body is in fight/flight exertion mode during heavy exercise; I thought maybe it was a paradoxical parasympathetic discharge. With exertion, though, I could be overheating AND accumulating metabolic acids, couldn't I? 

Avatar of:

Posts: 0

December 7, 2011

Hmm.  I have fits of yawning whenever I work out with my athletic trainer.  It's always disconcerting because my body is in fight/flight exertion mode during heavy exercise; I thought maybe it was a paradoxical parasympathetic discharge. With exertion, though, I could be overheating AND accumulating metabolic acids, couldn't I? 

Avatar of: Dana Vaughan

Dana Vaughan

Posts: 2

December 7, 2011

Hmm.  I have fits of yawning whenever I work out with my athletic trainer.  It's always disconcerting because my body is in fight/flight exertion mode during heavy exercise; I thought maybe it was a paradoxical parasympathetic discharge. With exertion, though, I could be overheating AND accumulating metabolic acids, couldn't I? 

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