Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/778/
722 D 
PHYSIOLOGY OF THE NERVOUS SYSTEM. 
of fibres in each muscle, which, to be effective, 
must have the same relation to the component 
elements of the muscle. It is impossible to 
imagine how each order of fibre should comport 
itself with reference to the other two, so that 
their actions may not interfere. Nor can any 
one fail to perceive that the emotional fibres 
must be infinitely less frequently employed 
than the others, and in some individuals so 
seldom called into action as to be greatly ex¬ 
posed to the risk of atrophy for want of use. 
Another phenomenon, which this hypothesis 
fails to explain, is the paralysis of the sphincter 
ani muscle which accompanies certain lesions 
of the brain, generally of grave import. Such le¬ 
sions are almost always accompanied by para¬ 
lysis, chiefly of the hemiplegic kind, but not ne¬ 
cessarily complete. On the contrary, in several 
such cases distinct reflex actions exist, indicating 
that, although the brain’s influence is withheld 
from the limbs, that of the cord is not. If, 
then, the cord be sufficiently free from morbid 
depression to allow of reflex movements taking 
place in the inferior limbs, why is the sphincter 
ani (the actions of which according to Dr. 
Hall are eminently reflex) so completely para¬ 
lysed that it offers not the slightest resistance 
to the introduction of the finger into the anus ? 
So long as the cord is free from lesion and so 
capable of performing its functions that the 
lower limbs exhibit reflex movements, the 
sphincter ani muscle ought not to be paralysed, 
if the excito-motor hypothesis be true. For, 
admitting that this muscle has sensori-volitional 
fibres which are paralysed by the cerebral le¬ 
sion, it should have excito-motor fibres likewise 
which ought to enable the muscle to resist the 
entrance of the finger into the rectum. Such 
resistance, however, it certainly does not make, 
for the muscle is completely paralysed in 
the cases referred to. And it is plain that, ac¬ 
cording to the excito-motory hypothesis, a cere¬ 
bral lesion ought not to affect the sphincter ani 
further than to destroy the control of the will 
over it, unless the depressing influence of the 
lesion extend to the whole cord, and in such a 
case there ought to be complete paralysis of the 
limbs likewise. 
In fine, it cannot be denied that the excito- 
motor hypothesis takes a narrow and confined 
view of that power of the nervous centres which 
it professes to elucidate. As I have before 
remarked, it limits this power to the excitation 
of motion, and it confines the exciting agency 
to nerves which naturally propagate centrad, 
and which only propagate such impressions as 
may excite movements. 
Now it admits of unquestionable proof that 
impressions on sensitive nerves may, by a pro¬ 
cess of reflexion, excite other sensitive nerves. 
Are we to suppose the existence of a special 
series of fibres for such phenomena? Such 
a supposition would involve the most palpable 
contradictions, and is wholly inadmissible. 
The second hypothesis, which accords with 
the views of Müller, is just as competent to 
explain the phenomena of decapitated animals, 
and of limbs paralysed to cerebral influence, 
as that of Dr. Hall. It receives considerable 
support from the universal concurrence of sen¬ 
sation or mental perception with those normal 
actions which Dr. Hall would attribute to excito- 
motory fibres. If it be supposed that these 
fibres have a certain relation to the vesicular 
matter of the cord, there are as good grounds 
for the further supposition that they may con¬ 
tinue to be affected by it after the brain has 
been separated from the cord. This hypothesis, 
however, is as inadequate as that of excito- 
motory fibres to explain the influence of emotion 
on paralysed limbs; and it likewise fails to 
explain the paralysis of the sphincter, which, 
under this hypothesis, ought to occur in every 
case of cerebral disease. The chief objection, 
however, to this hypothesis is anatomical ; for 
it is far from being proved that the fibres of the 
spinal nerves are continued upwards through 
the cord into the brain. For instance, what 
evidence have we that the fibres of the lumbar 
region of the cord pass into the brain? The 
fibres of the anterior pyramids, no doubt, are 
true cerebro-spinal fibres, because they com¬ 
municate equally with brain and cord, and 
distinctly pass from the one to the other; but it 
cannot be shown that they have any continuity 
with the fibres of any of the spinal nerves. 
Much less can it be shown that they contain 
the fibres which are continued up from, to say 
the least, the anterior roots of all the spinal 
nerves, which ought to be the case if this 
hypothesis be correct. The bulk of the pyra¬ 
mids is very much opposed to this view. It is 
most probable that the pyramids are cerebro¬ 
spinal commissures. The apparent longitudinal 
course of the fibres in the spinal cord affords no 
indication that they pass into the brain, for 
it is well known that many of the fibres forming 
the roots of spinal nerves take a very oblique 
course from their point of separation from the 
cord to their emergence from the spinal canal ; 
and it is probable that this obliquity is con¬ 
tinued in the cord itself, so that their real 
origin would be much higher up than their appa¬ 
rent one. This great length of oblique course 
gives to the fibre the appearance of being strictly 
longitudinal, whereas it may be implanted in 
the vesicular matter of the cord. 
The third hypothesis is more consonant than 
either of the others with what appears to be the 
true anatomy of the spinal cord—namely, that 
each segment has its proper nerves implanted 
in it, that it is connected with adjacent seg¬ 
ments by commissural fibres, and that the 
whole cord is connected with the cerebrum 
and cerebellum by commissural fibres ; by the 
anterior pyramids and olivary columns with 
the former, and by the restiform bodies with 
the latter. 
This hypothesis, the reader will bear in mind, 
assumes that mental and physical actions are 
performed through the same fibres—affected by 
a mental stimulus in the one case, and a physical 
stimulus in the other—the change produced by 
the physical stimulus being, in the case of 
reflex actions, reflected at the centre. The 
same afferent and efferent fibres are excited in 
the one case as in the other, the former acting 
as sensitive or excitor, or both; the latter as
        

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