Bauhaus-Universität Weimar

The all-or-nothing response of sensory nerve fibres
Adrian, E. D. Alexander Forbes
so closely with, that for contraction that they are not shown in the 
figure, but it is notable that in general the size of action current in 
the case of motor nerve stimulation exceeds that in the case of reflex 
stimulation, more than the corresponding contraction exceeds the reflex 
contraction. This may be explained by the fact that the duration of the 
action current is far briefer than that of the contraction, and conse¬ 
quently the action currents of the individual fibres overlap less when, 
as in the reflex, they fail to occur simultaneously. The diminution of the 
galvanometric excursion, due to lack of synchronism, would be especially 
marked with diphasic action currents, for the second phase in some fibres 
would tend to neutralise the first phase in others, but we found that it 
was still present after the response had been made monophasic. The 
action current of the muscle in maximal response to motor nerve stimu¬ 
lation was so large in some experiments that the shadow of the string 
left the film. In most experiments a second series of records was made 
with the string much tighter and therefore able to record maximal 
responses on the film. Thus, we obtained enough records to show that 
as far as magnitude of response was concerned, the mechanical con¬ 
traction sufficed to yield all necessary data for plotting curves. The chief 
value of the galvanometer record was in showing when double response 
occurred in either afferent nerve or muscle. 
It will be seen that in the case of motor nerve stimulation when the 
break shock has attained a value of from 5 to 15 units1 (see above) the 
size of muscular response ceases to increase, the curve thereafter pre¬ 
senting a well sustained “plateau.” In the case of reflex stimulation 
the curve of muscle response, electrical or mechanical, presents a similar 
plateau, but not beginning till the stimulus is from 10 to 40 units, and 
not so well sustained as with motor nerve stimulation. The bend in the 
curve is not so sharp, and the response continues to increase slightly 
as the stimuli increase, even after the curve has become nearly flat. 
Only in the first of the three preparations did the reflex response of the 
muscle ever become greater than the maximal twitch (Fig. 13), and this 
was so only in the case of the mechanical response; the reflex electrical 
response remained throughout much smaller than that of the maximal 
Turning to the action currents of the afferent nerve subsequently 
obtained in response to a similar series of stimuli (Figs. 13 b, 14 b), they 
1 As nearly as we can judge by comparing our series of experiments with those of 
Forbes and Gregg, the unit here used is about two or two and a half times as large as the 
Z unit: see A. Forbes, Amer. Journ. Physiol. 56, p. 288. 1921. 


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