In the squid giant axon, Sjodin and Mullins (1958), using 1 msec duration pulses, found a decrease of threshold with increasing temperature, while Guttman (1962), using 100 msec pulses, found an increase. Both results are qualitatively predicted by the Hodgkin-Huxley model. The threshold vs. temperature curve varies so much with the assumptions made regarding the temperature-dependence of the membrane ionic conductances that quantitative comparison between theory and experiment is not yet possible. For very short pulses, increasing temperature has two effects. (1) At lower temperatures the decrease of relaxation time of Na activation (m) relative to the electrical (RC) relaxation time favors excitation and decreases threshold. (2) For higher temperatures, effect (1) saturates, but the decreasing relaxation times of Na inactivation (h) and K activation (n) factor accommodation and increased threshold. The result is a U-shaped threshold temperature curve. R. Guttman has obtained such U-shaped curves for 50 µsec pulses. Assuming higher ionic conductances decreases the electrical relaxation time and shifts the curve to the right along the temperature axis. Making the conductances increase with temperature flattens the curve. Using very long pulses favors effect (2) over (1) and makes threshold increase monotonically with temperature.
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1 May 1966
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May 01 1966
Theoretical Effect of Temperature on Threshold in the Hodgkin-Huxley Nerve Model
Richard Fitzhugh
Richard Fitzhugh
From the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Bethesda
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Richard Fitzhugh
From the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Bethesda
Received:
September 09 1965
Online ISSN: 1540-7748
Print ISSN: 0022-1295
Copyright © 1966 by The Rockefeller University Press
1966
J Gen Physiol (1966) 49 (5): 989–1005.
Article history
Received:
September 09 1965
Citation
Richard Fitzhugh; Theoretical Effect of Temperature on Threshold in the Hodgkin-Huxley Nerve Model . J Gen Physiol 1 May 1966; 49 (5): 989–1005. doi: https://doi.org/10.1085/jgp.49.5.989
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