Electrodiffusion of Ions across a Neural Cell Membrane
Electrodiffusion of Ions across a Neural Cell Membrane
The Nernst–Planck equation describes the diffusion of ions under the influence of an electric field. Here, it is applied to describe the movement of ions across a neural cell membrane. The top half of the Demonstration sets up the simulation, while the bottom displays the results.
You can select the ions ,,,, which play key roles in neural dynamics, and vary their interior and exterior concentrations using the sliders (shown in dotted and dashed green). The electric field across the membrane is assumed constant so that the potential is linear, as shown in the left plot. You can choose from three different initial concentration distributions, shown by a dashed blue line in the right plot. The total simulation time can be set to either a relatively short or a longer time (slight delay to update).
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Na
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Κ
2+
Ca
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Cl
Once the parameters are set, click the "run simulation" button to generate the time development of the ion concentration, shown in solid blue. Move the simulation time slider to view the evolution of the distribution in time. If the parameters are changed, the curve turns to a dashed gray to indicate that the simulation should be run again. Equilibrium for the concentration of a single ion occurs when the potential is set to the Nernst reversal potential and the initial distribution is set such that there is zero ionic current, each shown in brown in the left and right plots.