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Yawning is a reflexive and often repetitive physical action characterised by opening the mouth wide, taking in a deep breath, experiencing a brief peak, and then exhaling shortly. When stretching and yawning happen at the same time, it's called 'pandiculation'. This isn't just a simple mouth opening; it involves a coordinated movement where the neck flexes and then extends, the pharyngolarynx (throat) widens, and the diaphragm and postural muscles stretch. Yawning is an involuntary action, and only humans seem able to change how often it happens for cultural or social reasons. It's highly stereotyped because the sequence of movements remains the same, regardless of environmental factors. Yawning is observed in both cold and warm-blooded animals, ranging from reptiles with basic brains to human primates, and it occurs in various environments (water, air, and land). 


  1. The Universal Yawn: the most common in vertebrates and is linked to things like sleep, waking up, feeling hungry, or being satisfied.

  2. The Emotional Yawn: found in certain mammals, especially those with a more developed brain. This type of yawn seems to help calm our nervous system after a stressful situation. For example, dogs might yawn more at the vet, and captive chimpanzees might do it when feeling uneasy. In humans, athletes, skydivers, and actors tend to yawn before intense moments, possibly because yawning helps reduce stress.

  3. The Contagious Yawn: occurs in apes and humans with a good understanding of other people's thoughts. This ability is absent in some autistic individuals. When we yawn after seeing someone else yawn, it activates parts of our brain associated with empathy. So, in a way, contagious yawning is a sign of involuntary empathy.


Despite the progress made in understanding how the brain controls yawning, there's still a lot research to be done. More studies are required to figure out how different chemicals in the brain work together, and which specific parts of the brain and receptors are responsible for making us yawn or stopping it. If we can fully understand this, it not only helps in developing medication that can target specific receptors for different effects but also enhances our knowledge of how things like diet or long-term medication might affect yawning. In simpler terms, we're still exploring the details of how yawning is controlled in our brains.


In ancient times, Hippocrates believed yawning helped release accumulated air in the body, similar to steam escaping from boiling water. This idea persisted until the 17th century. Shortly after, Santorio Santorio, proposed a theory linking yawning to abundant perspiration. He associated yawning and limb stretching after sleep with increased sweating, suggesting that these actions help the body release excess sweat. Johannes de Gorter, in the 18th century, contributed to the understanding of yawning by suggesting it improved brain oxygenation. This idea persisted for two centuries, with many attributing yawning to the body's need for better blood circulation and increased oxygen to the brain.


However, more recent studies have challenged this notion. Research by Provine et al. in 1987 showed that exposing healthy individuals to high levels of carbon dioxide or engaging in physical exercise did not increase yawning. Similarly, high levels of oxygen had no impact on yawning rates. Contrary to the belief that yawning improves brain oxygenation, evidence suggests that yawning does not increase during periods of low blood oxygenation.

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