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. 1970 Apr;65(4):884–891. doi: 10.1073/pnas.65.4.884

Nerve Membrane Excitation without Threshold*

Kenneth S Cole 1,2, Rita Guttman 1,2,†, Francisco Bezanilla 1,2,‡
PMCID: PMC282999  PMID: 5266158

Abstract

Evidence is presented to show that for a squid axon membrane the potential response, V, is a smoothly continuous function of a stimulating current, I. This makes it unlikely that an all-or-none or sharp transition phenomenon is a major factor in the processes by which ions cross the normal squid axon membrane and, probably, other excitable membranes.

Spatially uniform V and I were first produced in the squid axon with internal and external electrode arrangements and later by isolating a short length of axon between external pools of sucrose. Under these simplified conditions, direct experiments and calculations based on the Hodgkin-Huxley empirical conductances agree in showing that the maximum response, R, is a continuous, single-valued function of the effect of the stimulus, S. The maximum value of ΔR/ΔS decreased steadily as the temperatures were increased from 25° to 38°C. Uncontrolled fluctuations prevented direct observations of ΔR/ΔS below 15°C where calculations showed that it rose rapidly as the temperature decreased. Since the conductances are experimental parameters and since ΔR/ΔS as calculated from them remained finite and continuous event at 6.3°C, this is experimental evidence against an all-or-none threshold excitation.

However there is an all-or-none threshold for the initiation and propagation of an impulse along an axon where V and I are functions of both time and distance.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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