An Electro-Diffusion Model for Computing Membrane Potentials
and Ionic Concentrations in Branching Dendrites, Spines and Axons
Ning Qian and Terrence J. Sejnowski, Biol. Cybern. 1989,
62:1-15. Download the
full paper (PDF file)
Abstract
The Nernst-Planck equation for electro-diffusion was applied to axons,
dendrites and spines. For thick processes (1 um) the results of computer
simulation agreed accurately with the cable model for passive conduction and
for propagating action potentials. For thin processes (0.1 um) and spines,
however, this cable model may fail during transient events such as synaptic
potentials. First, ionic concentrations can rapidly change in small
compartments, altering ionic equilibrium potentials and the driving forces for
movement of ions across the membrane. Second, longitudinal diffusion may
dominate over electrical forces when ionic concentration gradients become
large. We compare predictions of the cable model and the electro-diffusion
model for excitatory postsynaptic potentials on spines and show that there are
significant discrepancies for large conductance changes. The electro-diffusion
model also predicts that inhibition on small structures such as spines and
thin processes is ineffective. We suggest a modified cable model that gives
better agreement with the electro-diffusion model.
Back to Qian Lab Home Page