Bauhaus-Universität Weimar

Titel:
Handbook for the Physiological Laboratory. Text
Person:
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit18583/407/
398 
INDEPENDENT MUSCULAR IRRITABILITY. 
of the poison, however much the rest may have been subjected to 
the action of the poison, the muscle may be thrown into con¬ 
tractions by stimuli applied to any part of the course of the nerve. 
The presumption is, that urari acts on the extreme ends only of the 
nerve, possibly on the end-plates. 
Yet, as we have seen, however much the muscles themselves be 
exposed to the action of the poison, they do not lose their irrita¬ 
bility. These two facts (1), that urari poisons the extreme peri¬ 
pheral ends of the nerves, and (2), that the muscles themselves do 
not under urari lose their irritability, form together a very strong 
argument for the view that muscles possess an independent irrita¬ 
bility of their own. 
Ohs. V. Get ready a nerve-muscle preparation. Place one 
pair of electrodes (A) (as far apart as practicable) on the muscle 
itself, another (B) on the nerve near the muscle, and a third (non- 
polarizable) pair (C) on the nerve also, a little higher up than B. 
Connect A and B with induction coils, and determine the mini¬ 
mum stimulus required to be sent through each pair of electrodes 
in order to produce a contraction in the muscle. It will be as 
well to record the contraction by means of the lever, &c. The 
irritability of the nerve (electrodes B) and of the muscle and 
nerve together (electrodes A) will thus .be respectively deter¬ 
mined. 
Now pass through C a strong ascending constant current ; and 
while the current is passing, determine as before the minimum 
stimulus for A and B. By the ascending constant current the 
portion of nerve between the electrodes C and the muscle has 
been thrown into a state of anelectrotonus ; and it will be found 
that the irritability of the nerve in this region has been very con¬ 
siderably lowered ; or, if the polarizing current be strong enough, 
and the pair of polarizing electrodes far enough apart, has been 
suspended altogether. Contractions in the muscle are either en¬ 
tirely absent when a shock is sent through B, or only appear when 
the shock is very strong. At the same time it will be found that 
the minimum stimulus of A is not very different from what it 
was before. A rather stronger stimulus is required to produce a 
contraction, but the difference is strikingly less than that in the 
case of the electrodes B, and even this difference may be accounted 
for by considering that the electrodes A stimulate both the muscu¬ 
lar fibres and the intra-muscular nerve fibres, and that the com¬ 
bined effect is therefore greater when the intra-muscular nerves 
are intact than when they are paralyzed by the ascending cur¬ 
rent. 
Thus the ascending current will, if strong enongh, suspend 
the irritability of the nerve fibres supplying a muscle, and yet 
will leave the muscle but little altered in its susceptibility to
        

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