Friday, 3 July 2015

What is the Scientific Reason of Yawning?

Yawning!  one of the most under-appreciated behaviors. Yawning is one of the first things we learn to do. Or in fact we do not even need to ‘learn’. The human fetus yawns during its first trimester in the womb and continues to do it after birth throughout his life. As we yawn unconsciously and spontaneously, we at times can’t stop ourselves from yawning even at the most inappropriate moments. Animals do it, too. But why, exactly, do people and animals yawn? No one knows for sure. But there are many ideas about why people yawn.

People report to yawn more frequently when they are bored or tired. This shows that boredom, fatigue and hunger do reliably elicit yawns. One idea is that, when we are bored we just don’t breathe as deeply as we usually do. This causes a deficit of oxygen which is required for our metabolism. Therefore yawning actually helps us bring more oxygen into the blood and remove more carbon dioxide from the blood. Thus, yawning does seem to grow more intense when we’re feeling subjectively sleepy. This idea would imply that yawn is an involuntary reflex to help us maintain our blood oxygen (prevent hypoxia) and carbon dioxide levels. But studies suggest no direct relation between blood oxygen / carbon dioxide and yawning.

A study, published online in April in the journal Physiology & Behavior, found a greater number of participants yawned more in the summer than in winter. Does yawning have to do with temperature? Actually yes! A leading hypothesis is that yawning plays an important role in keeping the brain at its cool, optimal working temperature. Stress or anxiety can therefore stimulate yawning as it causes the temperature of brain to rise and yawning helps to correct it in order to maintain the working efficiency of brain. As boredom and sleep stimulate yawning, it may serve to revive our body and keep us ‘alert’. In fact it was found that yawning actually enhances the physiological activity which suggests that some sort of waking up has been done.

As yawn is a coordinated movement of the thoracic muscles in the chest, diaphragm, larynx in the throat, and palate in the mouth, a theory suggests that yawning is actually a protective reflex to improve the lung compliance, as it redistributes the oil-like substance called surfactant that keeps the lungs lubricated and prevents alveoli from collapsing, by reducing the surface tension. Yawning stretches the lungs and lung tissue and therefore brings about a more even distribution of the surfactant.

Another mystery about yawning is that is seems to be contagious. Even reading about yawning can make you do it. While all animals yawn, contagious yawning has been found to occur in only humans, chimpanzees and possibly dogs. Scientists have explained contagious yawning primarily as an expression of empathy, and theorized that contagious yawning is a shared experience that promotes social bonding; it also ensures that in a group every one’s brain is alert.

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