Bauhaus-Universität Weimar

Titel:
The all-or-nothing response of sensory nerve fibres
Person:
Adrian, E. D. Alexander Forbes
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit27729/3/
ALL-OR-NOTHING RESPONSE. 
303 
If this evidence can be accepted it is clear that we have a possible 
explanation of grading in the sensory nerve fibres. 
As the experiments bearing on this point did not seem to us altogether 
conclusive we have tried to determine how far the size of the impulse 
can be made to vary with that of the stimulus in a fibre which conducts 
with a decrement, and we have then examined various mammalian nerve 
trunks and reflex preparations to see how far this will account for the 
grading in a reflex arc. 
Response to stimuli in a region of decrement. It has been shown in the 
frog’s nerve-muscle preparation that when an impulse set up on the 
proximal side of a narcotised region fails to reach the muscle, it fails 
for all strengths of stimulus, i.e. an increase in the stimulus does not 
increase the capacity of the impulse to pass through the region of 
decrement. Thus the size of impulse which can be set up in a normal nerve 
is independent of the strength of stimulus. But Lodholtz(4) and 
Rehorn(5) have shown that if the stimuli are applied within the décré¬ 
mentai region there is a stage of narcosis in which the strength of stimulus 
required to set up an impulse which will pass to the muscle is greater 
and greater the longer the distance which the impulse must travel in 
the region. Since the local excitability must be the same throughout, 
it appears to follow that the impulse set up by a weak stimulus can only 
travel a short distance without extinction, whereas that set up by a 
strong stimulus can travel further. Thus if an impulse is set up in a 
region of decrement the initial size seems to depend on the strength of 
the stimulus. Whether this conclusion is valid or not depends on whether 
the stronger stimuli are accurately localised. A strong stimulus might 
succeed where a weak one fails, because it could spread down the nerve 
and start the impulse from a point nearer the muscle. As the evidence 
on this point did not seem to be conclusive, we have repeated the ex¬ 
periment, with certain modifications, taking special precautions against 
current spread. 
The frog’s sciatic gastrocnemius preparation was set up in a chamber 
shown diagrammatically in Fig. 1, so that the nerve passed through 
three chambers 9-5 mm. in diameter, through which an alcohol solution 
could be passed. The nerve could be stimulated at the slots A or B by 
sending a current through the fluid from one chamber to the next; in 
the later experiments a third partition at A' gave a third point of 
stimulation. With electrodes of this form the danger of current spread 
is very slight. The stimuli used were single break shocks from a coreless 
induction coil. The primary circuit could be made or broken by the 
20—2
        

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