- YAWNING is one of those curiously modified
respiratory acts which has important
physiological and psychological relations, not
the least remarkable of the latter being what
might almost be called its "infectious " nature,
associated with imitation on the part of the
beholder, and which in some people may be
excited by thinking intensely of the act itself.
- C. Mayer in
Zeitschrifl f. Biologie (vol. Iv., 1921)
gives the results of his investigations in man
by inspection, laryngoscopy, and X rays.
- The act itself he divides into three phases:
- The initial phase, beginning with
inspiration, widening of the chest, descent of
the diaphragm and larynx until a certain depth
of descent of both is reached, elevation of the
wings of the nostrils, of the soft palate,
drawing of the tongue upwards and backwards,
dilatation of the rima glottidis.
- The acme stage, full dilatation of the
thorax to its greatest extent by means of the
intercostal and accessory muscles, and descent
of the diaphragm and larynx to their lowest
position, accompanied by maximum depression of
the lower jaw, further retraction of the tongue,
and elevation of the soft palate. Tonic
contraction of a varying number of individual
muscles of the neck, shoulder, and region of the
trunk. Wide lateral expansion of the mouth,
closing of the eyelids, noise in the ears due to
contraction of the tensor tympani, and a
subjective feeling of pleasure and satisfaction.
- Final ihase, a short expiration, relaxation
of the contracted muscles, ascent of the
diaphragm and larynx, and elevation of the lower
jaw, secretion of tears, and deglutition.
- The duration of the tonic contraction of the
individual muscles is about 246 seconds, that of
the whole inspiratory phase (phases 1 and 2)
about 55 seconds.
- The biological significance of the acts
seems to lie in the energetic ventilation of the
lungs. The tonic phenomena accompanying the act
can only in part be explained by the irradiation
of the inspiratory impulses. This circumstance,
along with the accompanying stretching of the
arms and extension of the trunk, seem to
indicate that the act of yawning and the
participation therein of the pronounced
contraction of certain muscles is of importance
for aiding both the circulation and metabolism.
- The act itself would seem to be sub-cortical
in origin, though it may be excited or
discharged by psychical impulses. Spontaneous
yawning is an expression of cerebral fatigue and
the processes leading up to it stands in
intimate relation to the function of sleep. If
the optic thalamus is the part of the brain
intimately concerned with sleep, then at a
certain stage of fatigue the motor impulses for
the act of yawning may proceed from it.
- In certain cases of encephalitis
lethargica the execution of the act of
yawning may be disturbed and modified.
- Yawning the
- Yawning Lancet
- Yawning: its
physiology and psychology Lancet