Biographies de neurologues
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 L'histoire des neurosciences à La Pitié et à La Salpêtrière J Poirier
The history of neurosciences at La Pitié and La Salpêtrière J Poirier 

mise à jour du
23 mars 2008
J Hered
An apology for yawning
Prof. F. H. Pike
College of Physicians and Surgeons, Columbia University, New York


YAWNING is commonly said to be a means of ventilating the lungs when they need it. Everyone knows that it is an involuntary act, and often excited by seeing some one else yawn; the real purpose of the act, however, has been very little studied. Prof. F. H. Pike, of the College of Physicians and Surgeons, Columbia University, New York, was asked for his opinion in regard to the evolutionary origin of yawning, and has sent the following remarks, with a warning that they are partly fact and partly hypothesis.
"Luciani in his Human Physiology, vol. 1, p. 438, speaks of a deep inspiration as a part of the general process of yawning. He regards it as the external expression of ennui, drowsiness, hunger, and the like, but it does not seem to me that the ventilation of the thorax is the primary object of yawning. On our present views of the nature of the stimulus to respiration, the ventilation of the thorax keeps pace with the changing hydrogen ion content of the blood. An increase in the concentration of the hydrogen ions is accompanied by an immediate increase in the depth or rate of the respiratory movements. There is normally a deeper inspiration than usual occurring every few breaths, and it does not seem probable that there is a sufficient accumulation of carbon dioxide in the blood under any ordinary conditions to require any extreme effort such as yawning would indicate if its main purpose were to ventilate the lungs. A little vigorous exercise will remove the immediate cause of yawning, but it will also result in a greater ventilation of the thorax and lungs than occurred during yawning.
Muscular movements
"Yawning, in a state of nature, involves certain attendant movements and sounds that are absent in the human subject, after a course in a young ladies' finishing school or any similar institution. The dog gives a sort of whine and stretches his other muscles, particularly those of the fore legs, as well as those of the head and jaws. I am more and more inclined to regard yawning as an expression of a state of approaching fatigue, very much analogous to the other stretching movements of muscles in general. It may be a sort of involuntary exercise to keep one awake until a safe place for sleeping may be found. There is always a little quickening of the faculties after a deep yawn, and this is more pronounced if there is an attendant stretching of the muscles. One might imagine that the impulse to sleep might begin to come upon an animal while still out in the open, and that, if no warning sign were present, he might lie down in the open and go to sleep in a place exposed to attack from enemies. The continued yawning may be sufficient to keep him awake until he can reach a place of safety. This particular kind of utility may be lacking in civilized man, but the whole mechanism persists unchanged. To a certain limited extent, yawning might be regarded as a vestigal function if regarded from this point of view alone. But I am not sure that yawning has ceased to be useful to civilized man. The onset of yawning may interrupt a process which might otherwise be carried to a harmful degree. A student begins to yawn in the evening, and, unless he resorts to some measures to overcome his drowsiness, the interruption to his work is likely to become so great that he seeks relief in sleep. If he employ measures to drive away his drowsiness, such as the use of strong coffee, a walk around the block, or other similar things, he may be able to go on working, but he is pretty certain later on to feel, more severely than ever, the effects of fatigue, and he may suffer great injury if he persists too long in disregarding these warning signs of nature.
"I think Luciani is right in regarding yawning as an expression of drowsiness, but I believe also that too much emphasis has been placed on the factor of ventilation of the lungs. As a matter of fact, if one yawns widely, there is a total cessation of the movements of the thorax and diaphragm during the period when the mouth is most widely open. This I attribute to the stimulation of the endings of the glossopharyngeal nerve in the pharynx and uvula by the stretching of these portions of the alimentary tract at that time. It is well known that stimulation of the glossopharyngeal nerve will stop all respiratory movements immediately. Such a cessation normally occurs during swallowing. At the moment anything touches the uvula, respiration ceases immediately. One can feel the stretching of the pillars of the fauces and of the pharynx and uvula, or, more correctly, the part of the soft palate immediately to each side of the uvula, when the mouth is widely open in yawning."
Not only is yawning a very primitive adaption (if, indeed, it be an adaptation) but it appears to go back to a remote stage of evolution, perhaps far below the age of mammals. On this point Dr. Pike remarks:
"In thinking over the matter superficially it appears that the primitive respiratory neuro-muscular mechanism is the part particularly concerned. In fishes, the respiratory system involves the musculature of the mouth and possibly of the pharynx, and the nerves concerned are the fifth, seventh, ninth, tenth and twelfth cranial. The diaphragm and the phrenic nerve have not yet made their appearance, and the intercostal nerves and muscles are not concerned in the respiratory movements. That is what I mean by the primitive neuro-muscular respiratory mechanism. The muscles of the face and pharynx are involved in yawning, and the fifth, ninth, tenth and twelfth cranial nerves are also involved. I do not know where in the animal scale yawning first appears, but I should imagine that we might expect it in all the mammals, and possibly in some of the poikilothermal forms. It seems to be present in birds. In some respects, it approaches the type of respiration that is seen in cases of approaching death. In such circumstances, we have again the participation of the primitive neuro-muscular respiratory mechanism. The mouth is opened widely, often with a quivering or unsteady movement, and the thorax does not participate to the same extent as in normal respiration. The movements of the thorax may persist, altered in rhythm, to be sure, but nevertheless present, during yawning. I think that this is further evidence of the fact that yawning is related to the primitive mechanism."
apology for yawning