Why do we yawn?
animals for that matter, yawn.
evidence to support these beliefs.
Scientists do not purport to know all of the biological mechanisms of
the yawn, but tend to agree that a yawn is an involuntary respiratory
reflex, which regulates the carbon dioxide and oxygen levels in the
blood.
Technically, a yawn is the reflex opening of the mouth followed by the
deep inhalation and slow exhalation of oxygen.
The very act of yawning is but one of a number of involuntary reflexes
controlled by the spinal and nerve centers.
Scientists speculate that the onset of a yawn is triggered either by
fatigue, or by sheer boredom as, at those times, breathing is shallow,
and little oxygen is carried to the lungs by the oxygen-toting
cardiovascular system.
When one yawns, his or her alertness is heightened, as the sudden
intake of oxygen increases the heart rate, rids the lungs and the
bloodstream of the carbon dioxide buildup, and forces oxygen through
blood vessels in the brain, while restoring normal breathing and
ventilating the lungs.
This quite plausible theory of yawning falls short of explaining many
aspects of yawning. Scientists explain away the "contagious" nature of
yawning, that is when one person's yawn triggers another nearby to
yawn, as due to the power of suggestion, but are at a loss when
attempting to explain why yawning occurs excessively in patients with
lower brainstem damage or with multiple sclerosis.
Other unlocked mysteries include why fetuses in the womb yawn, when it
is a well-known fact that they do not intake oxygen into their lungs
until after live birth, or why individuals with high concentrations of
oxygen in their blood streams yawn.
Until these questions are answered, do not assume that a person who
yawns in your presence is bored with what you are saying, or suffers
from exhaustion. Simply be pleased that he or she is not bored to
death.
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