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What Causes Yawning: What Is Its Function?
13.02.2024 02:30
Updated: 12.05.2024 23:40
The phenomenon of yawning is popularly associated only with fatigue or boredom. Is this correct? What are the physiological bases of yawning?
It is worth noting that yawning and stretching often accompany us in the morning, immediately after waking up, which already calls into question the popular belief that yawning is just a sign of fatigue.
What if we viewed yawning not as a symptom that prompts us to go to sleep, but as a mechanism that wakes us up? It turns out there’s some truth to this assertion.
Why do we yawn? What are the mechanisms of yawning?
A study was conducted in which participants were observed from 75 seconds before and 75 seconds after yawning. The measurements were compared between baseline (on average, 70 to 40 seconds before), the peak moment, and 5, 10, and 15 seconds after. After 15 seconds, there were no significant differences, everything returned to the baseline level, so the subsequent measurements were not included in the summary.
The main observation was a short-term but significant change in heart rate during yawning. An increase in heart rate may lead to improved blood flow (as indicated by an increase in facial skin temperature) and more efficient blood flow to the brain. This is due to activation of the sympathetic nervous system.
An increase in its activity is indicated by changes in skin conductivity, a parameter that determines the electrical resistance of the skin under the influence of the activity of the sweat glands, which is influenced by the sympathetic nervous system.
This effect is associated with a response to emotional stimuli, and similar measurements are made using lie detectors or biofeedback devices.
There is also a theory that yawning mechanically stimulates the carotid artery, promoting increased cortical arousal by applying pressure to the neck during yawning. The neck is highly vascular, and pressure may stimulate blood flow, causing stimulation by hormones such as adenosine or catecholamines.
A slowing of breathing was also noted shortly after yawning, which is counter to the hypothesis that yawning improves oxygenation. The effect of slowing breathing maintains oxygen balance more or less at the same level, despite the increase in lung capacity at the peak.
In another study, yawning observation was further directed at recording the phenomenon with a video camera in order to expand the volume of data for analysis and improve the accuracy of the conclusions drawn. Yawning is a long, deep inhalation, a short pause, and a quick exhalation.
It is important to distinguish which effects are specific to yawning and which are simply related to taking a deeper breath, so this study compared the effects with those caused by simply taking a deep breath, not associated with yawning. It was noted that the increase in heart rate also occurred during inhalation without yawning.
The study's conclusion shows that both yawning and deep inhalation increase facial temperature, heart rate, and lung capacity. The effect of yawning, but not inhalation itself, was to activate the sympathetic nervous system.
Based on the observations of these studies, the authors of the publication consider yawning to be the brain's cooling mechanism as the most likely hypothesis, since yawning makes blood circulate more efficiently, and faster blood flow to the brain is a factor that lowers its temperature. This corresponds to the circadian rhythm - we yawn the most in the evening, and just before sleep the brain reaches its highest temperature.
With regard to the thermoregulatory effect of yawning, experiments were also conducted on rats, where it was found that brain temperature rises shortly before yawning and then quickly falls after it.
Why do we yawn in the morning?
Let's go back to the morning yawn for a moment. Where does it come from? Time to get some biochemistry! The melanocortin system, specifically the MC4 receptors, are involved in yawn initiation. These receptors are activated by melanocortin compounds, as well as ACTH, which is activated sharply in the morning, increasing cortisol levels.
It is possible that this is an additional effect, which, in addition to the activating action of cortisol, consists of increasing the blood supply to the brain and stimulating it to start the new day at full strength faster.
You probably know this effect when someone yawns and you do the same right after? This is also of interest to scientists, as one hypothesis concerns the development of social and empathetic communication as a function of yawning. This is the effect of mirror neurons.
It was previously reported why you should eat parsley root .
