Electrostatic pressure relates to the tendency for sides with two different electric potentials to become equal. At the resting potential of around -70mV, the inside of the neuron is much more negative than the extracellular space. This is largely due to large negatively-charged proteins inside the cell that cannot leave the cell. The net outflow of positive charge from the sodium-potassium pump is also a factor. To make the intracellular space more positive, there will be electrostatic pressure trying to push positively-charged ions into the cell.
Meanwhile at resting potential, the cell is using ATP to bring in 2 potassium ions and push out 3 sodium ions. So we get something like this:
[Na]outside cell > [Na] inside cell
[K]outside cell < [K] inside cell
Diffusion force will make the ions want to have the same concentrations inside and outside the cell. So the force will try to push potassium out and sodium in.
Here is a summary of what we have so far:
Diffusion force: bring Na in ->
Diffusion force: take K out <-
Electrostatic pressure: bring both Na and K in ->
In conclusion, the electrostatic pressure and diffusion force contribute forces that balance to create the -70mV resting potential.
