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- Introduction.
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- 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.
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- 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".
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- (..................)
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- Coughing.
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- 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.
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- 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.
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- 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.
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- Yawning.
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- 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.
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- 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.
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- 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.
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- Humming.
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- 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.
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- Laughing.
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- 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.
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