The act of yawning begins
during fetal life. The complex biochemistry
involved in this action includes many enzymes
and neurotransmitters, including: dopamine,
acetylcholine, muscarine, histamine, adenosine,
serotonin, nitric oxid, adrenocorticotropic
hormine, oxytocin, alpha-melanocyte hormone,
opioids and gammaaminobutyric acid.
An early research into
the physiology of yawning was conducted by
Charcot. His famous case was a woman with
relentless yawning who was hospitalized for
months in Salpetriere hospital. This patient
presented with a yawning frequency of 8 yawns
per minute, and Charcot noted that although her
breathing pattern was severely disturbed her
ventilation was not reduced.
Charcot then realized
that the patient's yawning was functioning as
deep inspirations replacing normal breathing
movements (breathing through yawning). A single
yawn can therefore be viewed as an isolated act
of hyperventilation in which the oxygen
saturation is increased and the PCO2
reduced.
etc...
Yawning is a signal
initiated by the reticular system and brough to
our consciousness, that a change in the
functional state of the nervous system occurs
and need help.
Any change in the steady
state as perceived by the brain provokes a
reaction by the reticular formation. Therefore a
yawn may be triggered by a diverse array of
states which represent a change in situation:
boredom, sadness, surprise, suffering, fatigue,
stress, somnolence...
The reticular system's
anatomy of intense proximity (under 2 inches) of
both activating and inhibitory neuronal networks
may explain why yawning appears in situation
which are seemingley paradoxal such as boredom
and excitation.
Inaccuracies in the
harmonic regulation function occurs on
pathologic basis, at different levels of the
central nervous system, such as the cortical,
limbic, hypothalamic and autonomic nervous
system, but always involving the essential
regulator "the reticular network".
