The idea that yawning and stretching can be related stems from the fact that it can be somewhat unsatisfactory if we try to stifle or prevent yawning by squeezing our jaws. It, therefore, seems to depend on various mechanisms that control yawning and breathing. Yawning is not caused by lack of sleep, but by a combination of factors such as stress, stressors and fatigue.
Hippocrates thought that yawning removed bad air from the lungs, like a fever, and Hippocrates himself thought it removed “bad air” from our lungs. It has been shown that people yawn more when they press a cold towel against their head than when they press a warm, room-temperature towel against their head.
In the 17th and 18th centuries, doctors believed that they yawned when environmental conditions, such as the temperature of the brain itself, increased. More recently, the consensus has shifted to the idea that yawning cools our brain by increasing oxygen, so that the amount of oxygen in our lungs increases during a “yawning” episode.
But despite these theories, the truth is that scientists do not know the true biological function of yawning. Although the reason has been elusive for thousands of years, recent research has revealed some truth about why we yawn, though not all well.
When a person yawns, stretching the strong jaw muscles increases blood flow to the head, neck and face and directs cerebrospinal fluid into the sinuses. In combination with the large opening of a gaping stomach, large amounts of air can be sucked in through the walls of our sinuses.
Many people assume that yawning serves to absorb more oxygen and exhale CO2, and assume that we yawn because our body tries to get rid of the extra carbon dioxide and absorb some of it. However, these principles of conventional wisdom have absolutely no objective evidence to support them. When people are bored or tired, they breathe in too much air and exhale too little oxygen, according to the American Heart Association.
The most popular answer is that yawning helps manage the build-up of carbon dioxide by increasing the flow of oxygen to the brain. A decade ago, it was shown that inhaling air polluted with high levels of CO2, such as high-pressure air, does not cause yawning and does not suppress pure oxygen. Yawn produces a signal that says, “Take a deep breath,” and this signals your body to exhale oxygen, which in turn leads to more oxygen in the lungs and less carbon dioxide in the blood, according to researchers at the University of California, Berkeley.
Gallup’s favourite explanation is that yawning is like sweating – a way to keep cool. The physical basis of yawning could explain why people yawn more often when they are anxious or stressed.
Gallup and his research also suggest that yawning can help cool the brain, because the cold air inhaled cools the blood, causing the blood to flow through the yawn. Gallup’s team found that people yawn more at cooler temperatures, and yawn is more likely to have a cooling effect when the air is hot than when it is cool.
Critics point out, however, that yawning seems to fail precisely when an organism needs it most: after eating, a snake reorients its jaw and yawns to encourage breathing.
Psychologists Andrew Gallup and Gordon Gallup believe yawning helps improve blood flow to the brain. If cortisol levels rise during yawning, this can increase alertness and indicate the need for action.
The premise is that stretching the jaw increases blood flow to the face, head and neck, with blood and spinal fluid flowing down. It seems that the brain heats up more than any other organ, so yawning sends large amounts of cool air into the nasal and oral cavity, increasing the speed of blood flow through the skull and changing the temperature of the blood – blood flow – of the cooling brain.
Moreover, the reason we feel better after a hearty yawn maybe because we yawn more when it’s cooler. We could also find that yawning increases blood flow to the brain in some climates, which in turn lowers the temperature of our brain.
Yawning is said to stimulate arousal and increase alertness when we are sleepy, and this effect is stimulated by a combination of the body’s natural reflexes, such as teeth grinding and inhalation. When we feel a yawn, we clench our teeth when inhaling, but others block yawning in the form of yawns while squinting eyes are a potential trigger for yawning, as facial features are associated with it.
There are receptors in the neck called carotid arteries, which in turn trigger yawns, as well as a number of other body parts such as the heart and lungs.
Yawning causes a deep inhalation that draws cold air into the mouth and then cools the blood that reaches the brain. Supporters of the theory claim that during yawning, an increase in brain temperature is observed, while during yawning, a decrease in temperature is observed. Research reports that led to this theory have only shown that excessive yawning can occur due to an increase in brain and body temperature.