Yawning is a reflex opening of mouth and simultaneous deep inhalation of air and stretching of the eardrums, followed by slow exhalation of breath. It is an involuntary action that we do without our consciousness, which causes us to open our mouths wide and breathe in deeply. When yawning includes stretching also , it is called pandiculation. We do yawn even when we are still in our mother's womb. Yawning can also be a powerful non-verbal message with different meanings depending on the circumstances. Yawning has an infectious quality (imitation) in humans like observing another person's yawning face, looking at a yawning picture, or just thinking of yawning can trigger a person to yawn, which is a typical example of a positive feedback. Yawning in animals serve as a warning signal, display of anger, aggressive attack, courtship ritual, confusion, and other physiological reasons.
Causes of human yawning
1. Drowsiness or weariness.
2. Excessive tiredness or boredom.
3. Disorder associated with excessive daytime sleepiness.
4. Panic.
5. Imitation.
Reason behind yawning
There are various theories put forward to describe yawning such as a) Physiological theory. b) Cooling of brain theory. c) Evolution theory. d) Boredom theory etc.
According to the brain cooling theory, yawning cools the brain when it is overheated. The brain is able to function at its best when it is cool and humans and other animals have evolved adaptations to accommodate this. Very often, when we are tired or under stress, we keep yawning all the time. It is caused as the deep brain temperature is increased, when the person is exhausted or sleep deprived. Yawning cools and alerts the brain.
Yawning is induced when the level of glucose supplied to the brain decreases such as in the state of hunger. It is also thought to be a mechanism to clear the lymphatic system before and after sleep. Another assumption in this regard is that yawning is caused by some chemicals found in the brain, like, serotonin, dopamine, glutamine, glutamic acid and nitric oxide. These chemicals are also responsible for affecting emotions, mood, appetite and certain other states. Activation of these chemicals in the brain is found to increase the frequency of yawns, while some other chemicals such as opioid neurotransmitters, e.g., endorphins, can reduce yawning.
The cause for contagious yawning (imitative yawning) may lie with mirror neurons that are neurons in the frontal cortex of certain vertebrates, which upon being exposed to a stimulus from the same species and occasionally interspecific organisms, activates the same regions in the brain. Mirror neurons have been proposed as a driving force for imitation which lies at the root of much human learning, e.g., language acquisition. Yawning may be an offshoot of the same imitative impulse.
Yawning in animals
Baboons yawn to threaten their enemies by displaying large canine teeth. A Siamese fighting fish yawn only when they see a their same species or their own mirror-image, and their yawn often accompanies aggressive attack. Guinea pigs also yawn in a display of dominance or anger displaying their impressive incisor teeth.Adelie Penguins yawn as a part of their courtship ritual. Penguin couples face off and the males engage in an ecstatic display. Snakes yawn to realign their jaws after a meal and for respiratory reasons. Dogs often yawn after seeing people yawn, and when they are confused. Fish can also yawn, and they increase this behavior due to lack of oxygen or excessive heat. Infectious yawning has also been noted in chimpanzees especially for psychological reasons and contagious yawning may have developed as a way to keep a group of animals alert.
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