The yawn is a behavior Réflexe, phylogenetically old, stereotyped but flexible and physiologically contemporary of the muscular stretchings during the awakening. It is insulated at the time of the need for sleep, the anguish, the hunger or the trouble and is present at the human and the animal , of the reptiles to the birds, in particular all the Mammifère S. The yawn is a banal physiological behavior, described as of the Antiquité by Hippocrates which thought that the yawn allowed the evacuation of the fever, as a chimney evacuates smoke. Forgotten after the publications of Jean-Martin Charcot, the Médecine of the 20th century did not attach there much interest until the Années 1980, marked by progress of the Neurophysiologie and the Neuropharmacologie which give again direction to him.

Physiological description

The cycle of the yawn proceeds in three phases followed by a feeling of wellbeing and relaxation: a long inspiration, a Apnea of approximately a second, during which the auditive acuteness decreases, and a fast expiry, sometimes accompanied by a stimulation of the lachrymal Glandes and associated or not with stretchings. Without improving the cerebral oxygenation , as that was repeated during centuries, the yawn seems a stimulation of our vigilance; he plays a part in the not-verbal communication in particular at the Primate S, at which he is related to the rate of Testostérone.

Whereas the yawn disappears in the extra-pyramidal syndromes (Parkinson's disease), the salvos of repeated yawns are pathological and can reveal multiple neurological or neuropsychological cerebral pathologies . The iatrogenic causes of yawns are frequent.

The cerebral trunk associated with the Diencéphale is the seat of this reflex but the curious phenomenon of the contagion of the yawn, specific to the man and the primates closest to the man (chimpanzee), implies the setting concerned of the frontal lobes (capacities of imitation and empathy). The Embryology and the Ontogénèse show parallelism between suction and yawn.

The course of the yawn utilizes many neuro-transmitters; the Dopamine plays a central role, by activating the production of Oxytocine by the core paraventriculaire of the Hypothalamus. The oxytocine activates the cholinergic secretion of the hippocampus and the Acétylcholine start the yawn by effect on the receivers muscarinic of the muscles of the Larynx, the Visage and the Mâchoire implied in its unfolding. Multiple projections of the core paraventriculaire on the locus coeruleus and réticulé of the cerebral trunk are the determinants of the effect of the yawn on vigilance. This too simplifying diagram omits others Molécule S also implied such NO, Glutamate, GABA, Sérotonine, ACTH, MSH, sex hormones, Hypocrétine and other neuro-peptides. This neurophysiological richness explains the interest of the observation of the yawn for pharmacological tests of new the Psychotrope S.

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