Professor of Medicine
(Retd.), TN Medical College, Hon. Physician,
Bhatia Hospital, Mumbai, Maharashtra
Yawning is a reflex of long deep inspiration
with mouth wide open and followed by slow
expiration. Yawns are often accompanied by urge
to stretch one's muscles. Stretching of the
hands is often accompanied or followed by
yawning. Act of yawning and stretching
simultaneously is called Pandiculation.
Yawning as a form of human and animal
behavior has defied all attempts to explain it.
However it is likely to be functionally basic in
serving very real organic need. In man yawning
occurs at all ages and in both sexes. Act of
yawning lasts about 6 seconds. Following are the
conditions under which yawning occurs:
Immediately before sleep, awakening from
un-refreshed sleep, weariness, lack of
stimulation, boredom or any monotonous task.
Medical conditions like multiple brain stem
ischemic strokes, frontal lobe tumors etc. may
cause excessive yawning. Psilocybin mushrooms
users often describe a marked stimulation of
yawning while intoxicated.
All these conditions have in common
&endash;lowered state of critical
consciousness-meaning state of normal, active
awareness of being related to environment. Any
significant decline may lead to yawning. Reduced
critical consciousness is often associated with
an increased CO2 saturation of blood. Yawning by
its massive inspiration of oxygen and exhalation
of CO2 serves to restore depleted oxygen content
of blood. The wide opening of mouth is
associated at the same time by stretching of ear
drums and movements of the mandible. The tongue
and the throat are some of the most overused
muscles of the body, used for speech, breathing
and swallowing. These muscles are stretched and
refreshed. Branches of internal and external
carotids and the veins emptying into jugulars
are compressed. Carotid bodies also probably get
compressed and contribute to alteration of
circulation. Tearing from the lachrymal glands
is often associated with yawning. This could be
due to pressure on the lachrymal glands or of
nervous origin or both. Possibly one of the
functions of lacrimation in yawning is to keep
the eyes well lubricated during changes in
pressure to which it is exposed. The flow of
tears through naso-lachrymal duct is enough to
lead to nose blowing. Higher levels of stress
hormones particularly cortisol, have been found
in the saliva of human subjects following
yawning. This has provided support for the
Thompson's Cortisol hypothesis which proposes
elevations of cortisol during yawning
episodes.
Yawning has long been observed to be
contagious. The social and biological function
of 'contagious' yawning would be to heighten the
consciousness of one's fellow by inducing
yawning in them. A study by the University of
London found that the "contagiousness" of yawn
by humans can pass on to dogs. Yawning warns one
of the reductions in critical consciousness and,
as in sleepiness or weariness, suggests that one
ought to sleep or rest; particularly while
driving. Yawning is often perceived as implying
boredom, and yawning conspicuously in an other's
presence has historically been considered
impolite; loud yawn in a courtroom has even lead
to penalty for contempt of the court !
This article was first published in
Meditheme (British Journal of Medical
philately)-May, 2014 issue; reprinted here in
abridged form with kind permission of the
Editor: Dr. S. W. Menzie
