Excitable cells generate action potentials. An unstimulated excitable cells is at a resting potential (Vm) which is due to the difference in ion concentrations on the inside and outside of the cell.
Nerve cells have a K+ equilibrium potential around -90mV.
Equilibrium potentials can be calculated using the 'Nernst equation' which is E = (RT/zF)LnCe/Ci
Leak channels are protein ion channels that cause the permeability of cell membranes to ions.
Neurons fire action potentials when they have been depolarized above the threshold level.