Membrane Electrophysiology: Resting Membrane Potential

Vocabulary flashcards summarizing essential terms and definitions from Dr. Reynolds’ lecture on membrane electrophysiology and resting membrane potential.

Resting Membrane Potential (RMP)

The voltage difference (≈ –70 mV in motor neurons) between the inside and outside of an excitable cell when the cell is not actively firing.

Sodium-Potassium Pump (Na⁺/K⁺-ATPase)

An ATP-dependent transporter that expels 3 Na⁺ ions and imports 2 K⁺ ions per cycle, creating and maintaining Na⁺ and K⁺ concentration gradients.

Concentration Gradient

Difference in the amount of a specific ion on either side of the membrane that drives passive diffusion from high to low concentration.

Electrical Gradient

Attractive or repulsive force created by separated charges across the membrane; like charges repel and opposite charges attract.

Electrochemical Gradient

The combined influence of an ion’s concentration gradient and electrical gradient that determines its net direction of movement.

Equilibrium Potential (Eₓ)

The membrane voltage at which the net flux of a specific ion is zero because its electrical and concentration gradients are equal and opposite.

Nernst Equation

Equation that calculates an individual ion’s equilibrium potential from its inside and outside concentrations: Eₓ = (61 mV/z) log([ion]ₒ/[ion]ᵢ).

Membrane Permeability

The ease with which ions cross the membrane; dictated by the number and state of open ion channels.

Leak Channel

Ion channel that is always open at rest, allowing passive ion movement (e.g., K⁺ leak channels greatly influence RMP).

Voltage-Gated Ion Channel

Membrane protein that opens or closes in response to changes in membrane voltage, central to action potential generation.

Ligand-Gated Ion Channel

Channel that opens when a chemical messenger (ligand) binds, altering membrane permeability to specific ions.

Action Potential (AP)

Rapid, transient reversal of membrane potential that travels along excitable cells, enabling electrical signaling and muscle contraction.

Depolarization

A positive shift in membrane potential (toward or above 0 mV) usually caused by inward Na⁺ or Ca²⁺ currents.

Repolarization

Return of the membrane potential toward the resting level after depolarization, typically via K⁺ efflux.

Hyperpolarization

A negative shift in membrane potential below the resting level, often produced by continued K⁺ efflux or Cl⁻ influx.

Motor Neuron

A nerve cell that innervates skeletal muscle and exhibits a resting membrane potential of about –70 mV.

Excitable Cell

Cell type (e.g., neuron, skeletal or cardiac muscle) capable of generating action potentials due to voltage-gated channels.

Steady State

Condition in which ion fluxes driven by pumps and leaks are balanced, keeping membrane potential constant over time.

Net Driving Force

The difference between the membrane potential and an ion’s equilibrium potential, determining the direction and strength of ion movement.

Hyperkalemia

Abnormally high extracellular K⁺ that partially depolarizes cells and can impair cardiac and neuromuscular function.

Hypokalemia

Abnormally low extracellular K⁺ that hyperpolarizes cells, making them harder to excite.

Hypernatremia

Elevated extracellular Na⁺ concentration; can influence cell volume and contribute to neurological symptoms.

Hypercalcemia

Excess extracellular Ca²⁺ that can reduce neuronal excitability and disrupt cardiac and skeletal muscle contraction.

Hyperchloremia

Increased extracellular Cl⁻ that can contribute to acidosis and alter resting membrane potential via Cl⁻ permeability changes.

Single Ion Equilibrium Potential

The membrane voltage predicted by the Nernst equation for one ion species at which its net movement is zero.