Apr 26, 2017

The basis of sharp spike onset in standard biophysical models

PloS One
Maria TelenczukRomain Brette

Abstract

In most vertebrate neurons, spikes initiate in the axonal initial segment (AIS). When recorded in the soma, they have a surprisingly sharp onset, as if sodium (Na) channels opened abruptly. The main view stipulates that spikes initiate in a conventional manner at the distal end of the AIS, then progressively sharpen as they backpropagate to the soma. We examined the biophysical models used to substantiate this view, and we found that spikes do not initiate through a local axonal current loop that propagates along the axon, but through a global current loop encompassing the AIS and soma, which forms an electrical dipole. Therefore, the phenomenon is not adequately modeled as the backpropagation of an electrical wave along the axon, since the wavelength would be as large as the entire system. Instead, in these models, we found that spike initiation rather follows the critical resistive coupling model proposed recently, where the Na current entering the AIS is matched by the axial resistive current flowing to the soma. Besides demonstrating it by examining the balance of currents at spike initiation, we show that the observed increase in spike sharpness along the axon is artifactual and disappears when an appropriate measure of ra...Continue Reading

  • References43
  • Citations6
  • References43
  • Citations6

Mentioned in this Paper

Vertebrates
Initial Segment of Axon
Extracellular
Bulla
Science of Morphology
Protoplasm
Resting Potentials
Neurons
Extracellular Space
Action Potentials

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