Bauhaus-Universität Weimar

668 
MOVEMENTS 
2. What regulates the rhythm of the respiratory movements? 
In the muscles of the extremities the power of continued action is evidently much 
greater than in the muscles engaged in respiration; thus we can continue standing or 
bear a weight for a long period, but can prolong the movement of inspiration or That 
of expiration only for a very limited time. Any muscular motion, however, may be 
persisted in for a very long period, if made to alternate with other motions. It is not, 
therefore, the nervous principle that is deficient in these cases, for there is nervous in¬ 
fluence sufficient for other muscular actions: the defect mfist be either in the con¬ 
ducting power of the nerves, or in the contractility of the muscles; one or the other 
of which, or perhaps both, are exhausted by the movement performed. The regular 
alternation of inspiration and expiration, and the regular succession of the three acts 
in the respiration of frogs, show pretty distinctly that neither of the preceding modes 
of explanation is sufficient to account for them; but that some unknown influence is 
in operation in the medulla oblongata, which causes each movement of the nervous 
principle towards the inspiratory muscles to be followed by a motion of the same 
principle towards the muscles of expiration, and vice versa; so that, as in a pendulum 
or balance, the movement in one direction necessitates the movement in the opposite 
direction. 
The respiratory movements are not the only periodic automatic muscular actions of 
daily occurrence which are due to the influence of the central organs of the nervous 
system. The motions of the muscles of the eye and of the iris during sleep present 
us with another example of these automatic muscular actions. During sleep the eye 
is turned somewhat inwards and upwards, and the iris is much contracted, although 
light is quite excluded. The eye takes this position even before sleep has come on; 
and the position of the double images which a person sees when he finds himself on 
the point of falling asleep, proves that the eyes are turned inwards. 
Automatic movements of the animal system with a persistent type. The sphincters of 
the animal system.—Although we have voluntary power over these muscles to 
strengthen their contraction, yet their action continues independently of volition 
during sleep as well as in the waking state, and it cannot be voluntarily interrupted, 
except by exerting a counter pressure against them by their antagonist muscles. The 
principal sphincters of the animal system are the sphincter ani and the sphincter 
vesicae, which is to a certain extent subject to the animal system of nerves. The 
force and impulse to contraction of these muscles are derived from the spinal cord. 
Injuries of the spinal cord cause their permanent relaxation, and the consequent in¬ 
voluntary escape of the faeces and urine; this relaxation of the sphincters sometimes 
also occurs under the influence of depressing passions, which have the effect of 
weakening the power of the cord. Dr. Hall has shown that the sphincter ani of the 
turtle remains contracted as long, but only so long, as the lowest portion of the spinal 
cord is left uninjured. 
The action of the sphincters must be owing to an incessant motor excitement of 
their nerves. In considering the antagonistic muscular action, however, we shall 
become acquainted with facts which prove that not the sphincters alone, but indeed 
all the muscles of the animal system, are subject to this constant motor excitement. 
We have thus seen involuntary movements partly of periodic character, partly per¬ 
sistent, which are dependent on the influence of the brain and spinal cord. The same 
phenomena are observed as symptoms of disease of the central organs of the nervous 
system; persistent as well as intermittent muscular spasms, muscular contractions 
often occurring at very regular intervals, involuntary motion of the head to and fro, 
trembling of the limbs and the tonic cramps returning at regular periods, are ex¬ 
pressions of morbid states of those organs. It is not known why the motions assume 
these characters; it has been observed merely that the enduring contractions more 
generally attend the diseases of a completely local and fixed nature, although every 
kind of disease of these organs is capable of giving rise to periodic convulsTve affec¬ 
tions. As a general rule, indeed, nearly all affections of the nervous system which 
are attended with muscular contractions come on in paroxysms; and even inflammation 
and For. Med. Rev. April. 1838.) The theory of Professor Müller, that the cause of the first 
respiration is the impression made on the medulla oblongata by the arterial blood, is clearly 
open to the objection that the blood could not be rendered arterial, and therefore could not 
excite the medulla oblongata, until respiration had been at least once performed.
        

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