# Does the Nernst equilibrium in a neuron for a specific ion represent the potential voltage that would be needed to bring the net to 0?

I am learning about the Nernst equilibrium in a neuron (along with the Goldman equation), and while I understand certain concepts individually, I struggle to bring it all together. The Nernst equilibrium is defined in terms of the reversal potential. That is, the membrane potential value needed to bring the net to 0. So, if there is a concentration gradient which generates the potential of 80mV, the Nernst equilibrium (reversal potential) would have a value of -80mV. Is this correct?

Now, the deviation from this equilibrium results in the electrochemical driving force. that is the difference between the membrane potential (which is the actual electrical potential) and the reversal potential. how is the membrane potential interrelated to the concentration gradient? Is the concentration gradient facilitated by the permeability of ions creating the membrane potential as a result?

Lastly, is the conductance of ions simply the degree to which the permeability to particular ion is allowed, and is modulated by the state of the membrane potential - Hyperpolarisation causes one particular ion to enter, depolarisation another.

I know there are several points and questions made here. I hope that it is relatively structured. As I have said, I myself struggle to put it all together in a coherent manner and make it more intuitive.

The Nernst equation gives the reversal potential/equilibrium potential, which is the voltage for which net flow for that specific ion equals zero. Net flow of zero for some ion means that the number of those ions moving out of a cell is equal to the number of those ions moving in.

The further the voltage is from the Nernst potential, the larger the 'effective' voltage is for that ion; that's the electrochemical driving force.

There is likely to be net current for other ions at the Nernst potential for a single ion; the purpose of the Goldman equation is to determine the voltage at which overall net current is zero. You can think of it like a weighted average of all the Nernst potentials, where each type of ion contributes more to the Goldman equation when there is more conductance across the membrane for that ion.

At any given moment of time, there is both the actual voltage, determined by the positions of charges and history, and the equilibrium potential, which you can calculate from the Goldman equation, the concentrations of all permeable ions, and the permeability of each ion. The actual voltage will get closer and closer to the equilibrium potential unless conductances change; the reason for this change in voltage is a net movement of ions (current), so the rate of change of voltage is given by the current.

if there is a concentration gradient which generates the potential of 80mV, the Nernst equilibrium (reversal potential) would have a value of -80mV. Is this correct?