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
The mechanisms of speech and deglutition
in progressive bulbar palsy
McDonald Crithley, Charles S. Kubik


The disturbances of function of the larynx and pharynx met with in disorders of the central nervous system are notoriously difficult to analyse; investigation into the morbid physiology entails a knowledge of many points in the normal working of these functions, which are still difficult of comprehension. The analysis of pathological cases, combined with investigations along the lines of comparative morphology and embryology, may contribute to our knowledge of the normal physiology. For this purpose, cases of bulbar palsy, arising in the course of amyotrophic lateral sclerosis, have been chosen. The choice was determined more by opportunity than by deliberation, as there are especial difficulties peculiar to Charcot's disease which arise when investigating these phenomena.
References to the relative affection of the bulbar muscles in this disease are scanty, and there are even fewer observations upon the morbid physiology of the larynx and pharynx. Hallopeau, in his thesis of 1875 on bulbar palsy, cited several cases in which paralysis of the laryngeal musculature occurred in the course of progressive muscular atrophy. Fatty changes were met with in the affected muscles. In his own words: "Les troubles de la phonation consistent dans une altération de la voix causée par un état parétique des muscles intrinsèques du larynx; rarement la voix est complètement éteinte, elle est seulement aaffaiblie... M. Duchenne a pu constater au laryngoscope le relâchement des cordes vocales".
This act can be brought about either by voluntary effort or by reflex action. In the latter case the receptive mechanism is represented by the mucous membrane of the nasopharynx, pharynx, larynx and trachea, and possibly also of some of the larger bronchi, as well as the mucous membrane of the external auditory meatus. These areas obtain their sensory innervation from the glossopharyngeal and vagal nerves.
The motor mechanism underlying coughing comprises a sudden forceful expiration of air through the opened mouth. The intrathoracic pressure is raised by contraction of the abdominal and thoracic musculature, particularly the latissimi dorsi and the recti abdominis, associated with a sphincteric closure of the glottis. When sufficient intrathoracic pressure has arisen, the sphincter abruptly relaxes, giving the typical explosive character to a cough. If the glottic sphincters are not made to participate in the act, a toneless and less forceful cough results.
Under certain pathological circumstances, as we shall see, the two phenomena of reflex and voluntary coughing may become dissociated, so that one is possible although the other cannot function.
This is a mechanism designed to clear out the dead space in the lungs and renew the residual air of the furthest alveoli. It can be brought about voluntarily, but it occurs more readily independently of the will under such well-known conditions as mental and physical fatigue, boredom and suggestion aroused by watching other individuals yawn. It frequently occurs shortly before the act of vomiting. In pathological cases it is sometimes met with in the form of uncontrollable bouts, such as occur after epidemic encephalitis.
The act is slow and deliberate in execution. It commences with a tautening of the elevators of the soft palate, the levator palat in particular. The jaws are widely opened and a prolonged inspiration occurs through a widely separated glottis; the inspiratory phase is succeeded by a prolonged expiration, often phonatory in character; this is followed by a period of expiratory apnoea. Other subconscious movements are frequently associated with yawning, though playing no essential part in the mechanism, as screwing up of the eyes, a bracing back of the shoulder-girdles, with abduction and extension of the arms. There is also a dilatation of the pharyngeal orifice of the Eustachian tube.
As already stated, the act may be initiated voluntarily by deliberate hardening and elevation of the palate. The reflex act, though occurring independently of the will, is not altogether beyond its control, as a yawn can frequently be inhibited, in part at least. As with coughing, the two nervous mechanisms are occasionally dissociated under pathological conditions.
This is produced in the same way as toneful phonation, except that the expiratory blast is directed through the nose instead of mouth. Escape through the buccal cavity is prevented either by compressing the lips or by elevating the back of the tongue against the soft palate. Variations in pitch are produced by alterations in position and tension of the vocal cords, together with elevation or depression of the larynx.
Laughter is a complex phenomenon arising normally as a physical concomitant of definite emotional states. As demonstrated by Graham Brown [1] and others, it is effected through definite psycho-faciorespiratory paths, passing from the cortex to the medullary nuclei. These pathways are completely independent of the pyramidal tract. Pyramidal activity is capable of partially inhibiting emotional laughter; it may also initiate a variety of laughter which, at the best, however. is only an imitation of the genuine act. The phenomenon is effected by expiratory blasts of air passing between vocal cords which are alternately adducted and abducted. The degree of adduction, however, does not equal that occurring during coughing. The movements of the vocal cords are accompanied by opening of the mouth and characteristic facial movements.