The compartmentalization of spike initiation
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1
UPMC, Institut de la Vision, France
According to the textbook view, spikes are initiated when the inward sodium current grows more rapidly with membrane potential than the outward potassium current, producing a positive feedback loop. This theory predicts that spike onset is smooth because sodium channels open gradually with voltage. In contrast, in cortical neurons, spikes recorded at the soma look “sharp”: spikes appear to suddenly rise from rest, as if all sodium channels opened at once. It has been proposed that sodium channels do open all at once in cortical neurons because of cooperativity effects. An alternative explanation is that spike initiation follows the textbook account in the axonal initiation site, but spikes are sharpened by active backpropagation to the soma. I will show that both explanations are incompatible with experimental evidence. I will then show that the sharpness of spike initiation can be explained by the compartmentalization hypothesis, which relies on the soma acting as a current sink for the axonal initiation site. The textbook view must then be modified as follows: spikes are initiated when the inward sodium current grows more rapidly with membrane potential than the axial resistive current flowing to the soma, producing a positive feedback loop. An important consequence is that the integrate-and-fire model is phenomenologically more accurate than the single-compartment Hodgkin-Huxley model of spike initiation.
Keywords:
action potential,
onset rapidness,
Biophysics,
spike initiation,
Sodium Channels
Conference:
Spike Initiation: Models & Experiments, Prague, Czechia, 22 Jul - 22 Jul, 2015.
Presentation Type:
Oral Presentation
Topic:
Neuroscience
Citation:
Brette
R
(2015). The compartmentalization of spike initiation.
Front. Neurosci.
Conference Abstract:
Spike Initiation: Models & Experiments.
doi: 10.3389/conf.fnins.2015.90.00003
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Received:
29 Jun 2015;
Published Online:
06 Jul 2015.
*
Correspondence:
Dr. Romain Brette, UPMC, Institut de la Vision, Paris, 75012, France, romain.brette@inserm.fr