Membrane Potential

Membrane Potential

(Vm) is the electrical potential difference

between the intracellular and extracellular environments of a cell.

Resting Membrane Potential

in non-excitable/excitable cells when they are at rest, typically between -50 and -100mV; RMV → determined primarily by its leak channels and gradients of ion(s) that are permeable through those leak channels.

Nerst Equation

Used to calculate the membrane potential Ex (Equilibrium Potential) or Nernst Potential for specific ions based on their intracellular and extracellular concentrations.

Nernst Potential

at which an ion is at electrochemical equilibrium at a given ion concentration gradient

Electromotive Force (EMF) or Net Electrochemical Driving Force

EMF is the difference between Vm and an ion’s equilibrium potential (EMF = Vm − EX), determining the direction of ion movement.

What Happens if EMF is Positive/Negative?

current is out/in, positive ions will move out/into the cell or negative ions will move into/out of the cell

Reversal Potential

(Vrev) for an ion is the membrane potential at which there is no net ion flux, equivalent to the ion’s Nernst potential (EX).

Electrical Relations to Lipid Bilayer, EMF, Conductance, and Vm

Capacitor, Battery, Variable Resistor, Sum of Equilibrium Potential and Conductance

Unitary Current

Current across a single channel when it is open

Electrically Polarized Membranes

Most cells maintain a membrane potential greater than zero,

resulting in electrical polarization.

Ohm’s Law in Membrane Transport

Ion current (IX) across the membrane is governed by Ohm’s law, expressed as IX = GX ⋅ EMF_X, where GX is the ion’s conductance.

Goldman-Hodgkin-Katz (GHK) Voltage Equation

determines Vm based on the permeabilities and concentrations of multiple ions, reflecting their combined contributions to the membrane potential.

Single Channel Conductance and Activity

The conductance and open probability of individual ion channels influence the overall ionic current and membrane potential dynamics.

Fractional Conductance and Vm Relationship

Vm is the weighted sum of each ion’s equilibrium potential, with weights determined by their fractional conductances (GX/Gm).

Hypothetical Cell Situation that would read 0mV on a voltmeter

ICF and ECF are nearly identical (electrolytes are =ly distributed), so there’s no charge difference ie not voltage difference ie no electrical or potential energy across membrane

Water moves from

areas of low solute concentration (high water concentration) to areas of high solute concentration (low water concentration).

The Na/K pump is

electrogenic, meaning it contributes directly to the membrane voltage by moving more positive charges out of the cell than into the cell.

No net movement of ions across concentration gradient

When the chemical force is balanced by an electrical force.