Resting Membrane Potential Lecture Notes

A comprehensive set of vocabulary flashcards covering the physiological mechanisms, ion concentrations, mathematical modeling, and clinical significance of the Resting Membrane Potential.

Resting Membrane Potential (RMP)

The electrical potential difference (voltage) across the plasma membrane of an excitable cell when it is in a quiescent or non-excited state.

Extracellular Fluid (ECF) Baseline

By convention, the extracellular environment is designated as a baseline of $0\,mV$, making the intracellular environment relatively negative.

Typical Neuron RMP

Approximately $-70\,mV$.

Skeletal and Cardiac Muscle Fiber RMP

Closer to $-90\,mV$.

$Na^+/K^+$ ATPase pump

An electrogenic antiport system that primary actively transports $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cytoplasm per $1$ molecule of $ATP$ hydrolyzed.

Net Electrogenic Effect of the $Na^+/K^+$ Pump

Contributes about $-4$ to $-5\,mV$ directly to the $RMP$ by transferring three positive charges out for every two it brings in.

Intracellular Concentration of Potassium ($K^+$)

High, approximately $140\,mEq/L$, resulting in an efflux chemical drive.

Extracellular Concentration of Potassium ($K^+$)

Low, approximately $4\,mEq/L$.

Intracellular Concentration of Sodium ($Na^+$)

Low, approximately $14\,mEq/L$, resulting in an influx chemical drive.

Extracellular Concentration of Sodium ($Na^+$)

High, approximately $142\,mEq/L$.

Selective Membrane Permeability Ratio

At rest, the plasma membrane is roughly $20$ to $100$ times more permeable to $K^+$ than to $Na^+$.

$K^+$ leak channels

Specifically inward-rectifier potassium channels that are high in density and remain open at rest, allowing $K^+$ efflux.

Fixed Intracellular Anions

Non-permeable anions such as proteins, $PO_4^{3-}$, and $SO_4^{2-}$ that accumulate on the inner face of the membrane as $K^+$ leaves the cell.

Equilibrium Potential ($E_{ion}$)

The exact voltage where the chemical driving force moving an ion down its concentration gradient is perfectly balanced by the electrical force pulling it back.

Nernst Equation

A formula used to calculate the electrical potential if the membrane were permeable to only a single ion.

Goldman-Hodgkin-Katz (GHK) Equation

A model used to determine the actual $RMP$ as a composite value based on the concentrations and relative permeabilities ($P$) of multiple ions.

Potassium Equilibrium Potential ($E_{K^+}$)

Determined to be $-94\,mV$ at physiological body temperature ($37^\circ C$).

Hyperkalemia

Elevated serum $K^+$ that decreases the concentration gradient, leading to hypopolarization (depolarization) of the $RMP$ and increased initial excitability.

Hypokalemia

Low serum $K^+$ that increases the concentration gradient, forcing more $K^+$ out and hyperpolarizing the membrane, which causes muscle weakness or paralysis.