"Transduction of graded synaptic input into trains of all-or-none action potentials (spikes) is a crucial step in neural coding.
Hodgkin identified three classes of neurons with qualitatively different analog-to-digital transduction properties.
Despite widespread use of this classification scheme, a generalizable explanation of its biophysical basis has not been described.
We recorded from spinal sensory neurons representing each class and reproduced their transduction properties in a minimal
model. With phase plane and bifurcation analysis, each class of excitability was shown to derive from distinct spike initiating dynamics.
Excitability could be converted between all three classes by varying single parameters; moreover, several
parameters, when varied one at a time, had functionally equivalent effects on excitability. From this, we conclude that the
spike-initiating dynamics associated with each of Hodgkin’s classes represent different outcomes in a nonlinear competition
between oppositely directed, kinetically mismatched currents. ..."
Prescott SA, De Koninck Y, Sejnowski TJ (2008) Biophysical basis for three distinct dynamical mechanisms of action potential initiation. PLoS Comput Biol 4:e1000198 [PubMed]