This September, like many other people, I joined a gym. From the first day I noticed that, despite my attempts to suppress it, I spent the bodypump class yawning. I wasn’t sleepy and I certainly wasn’t bored, but then what was happening to me?
He yawn It is a stereotyped movement that consists of a deep inhalation with the mouth open, a climax phase in which a maximum stretch of the muscles of the neck and pharynx occurs, and a short exhalation.
We perform this act since we are fetuses. Mammals, amphibians, birds, reptiles and even fish yawn. We yawn more in the interval between dream and vigil, in moments of stress (like some athletes before a competition) and with hunger.
Highly contagious
And of course, there are contagious yawns, which occur when we see someone yawn or even read about it. How many times has your mouth opened involuntarily since you started reading this article?
This is a common way of ecophenomenon (automatic imitation of another person), and is believed to be related to mirror neurons and hyperexcitability of the motor areas of the brain. We yawn more if the person who infects us is a family member and it happens to a greater extent to pregnant women. However, the scientific community does not agree on whether it is a phenomenon related to empathy, as is often thought.
In any case, 90% of the time we yawn spontaneously. So that?
It is not to oxygenate the brain
Let’s start by dismantling a false myth: we don’t do it to bring more oxygen to the brain. This theory was refuted more than 30 years ago, when it was shown that breathing high levels of oxygen or carbon dioxide or performing physical exercise did not influence yawning. Furthermore, the oxygenation hypothesis would not explain why the fetus does it.
It is true that the maximum stretching or lengthening of the muscles of the neck and pharynx that occurs during yawning would help tone these muscles. This seems to make them more efficient at opening the airways, therefore providing a greater amount of oxygen. However, this increase would be a long-term result, not an immediate effect.
So, if yawning does not serve a respiratory function, what is it for?
A cooling mechanism
Homeothermic animals like us regulate body temperature by establishing a balance between heat losses by convection (contact with fluids or air), evaporation (sweat) or conduction (due to contact with other objects). Temperature gains are mainly due to the cellular metabolism itself.
In the brain, temperature is regulated by the balance between blood circulation and heat generation by cells, and is usually at least 0.2°C above arterial temperature. Changes in brain activity, blood flow or inflammatory processes could alter this temperature.
Analyzing 1,291 yawns from 101 different species of mammals and birds, it was observed that the larger the brain size and number of neurons, the greater the number of times they yawned. That is to say, Larger brains, by generating more heat, would need to yawn more frequently.
Indeed, the exaggerated movement of the muscles of the neck and pharynx that occurs during yawning causes a significant increase in arterial blood flow to the face, neck and head, as well as a decrease in cerebrospinal fluid and venous blood from the head. This way we would be bringing a greater amount of blood at a lower temperature to the brain and removing, above all, warmer venous blood from it, which would help cool the organ and prevent damage from hyperthermia.
Furthermore, since the environment is normally at a lower temperature than our interior, that greater breath of air that occurs during yawning would cool the nasal passages, the paranasal sinuses and the area of the neck through which the carotid arteries that carry blood to the head pass. .
Interestingly, nasal breathing of cold air and cooling the forehead or neck reduce the frequency of contagious yawning. It has even been used as therapy in patients who suffer from excessive yawning due to thermoregulatory dysfunction.
Yawns to chase away sleep
Humans yawn more at night, when brain temperature is at its highest, and upon waking, when brain temperature begins to rise from its lowest point. By doing so we contribute to reducing brain temperature to maintain concentration and attention, thus counteracting sleep.
However, despite what we might think, we yawn more in winter than in summer. An experiment conducted with pedestrians in Tucson, Arizona, showed that the frequency of contagious yawning decreased with summer heat. When the ambient temperature is high, at first there is an increase in yawning to try to cool the brain, but these will soon be inhibited, so that they do not cause the opposite effect.
All this makes us predict that boredom heats up our brain. I’m hoping someone will investigate how it happens, because to cool it we already know what we have to do.
This article was originally published in The Conversation.
#reason #yawn #sleep
