(week 2 videos) Nernst Potentials and Resting Membrane Potential (Video Notes)

Flashcards covering Nernst equilibrium potentials for major ions (K+, Na+, Cl-, Ca2+), the resting membrane potential, electrochemical gradients, and the functional role of the Na+/K+ pump and membrane permeability in excitable cells.

What does the Nernst equation calculate for a specific ion?

The equilibrium (Nernst) potential Ex for that ion—the membrane voltage at which there is no net flux of that ion across the membrane.

What is the Nernst equilibrium potential for K+ when the membrane is permeable only to K+?

Approximately -90 mV (often around -87 mV); the chemical and electrical gradients balance so there is no net K+ movement.

What is the Nernst equilibrium potential for Na+?

+64 mV.

What is the Nernst equilibrium potential for Cl-?

Approximately -89 mV.

What is the Nernst equilibrium potential for Ca2+?

+129 mV.

What is the resting membrane potential (RMP) as given in the notes?

Approximately -70 mV (often cited as between -70 and -80 mV).

Why is the resting membrane potential closer to EK than ENa?

Because the membrane is more permeable to K+ than to Na+, so the RMP is dominated by the K+ equilibrium potential.

What are the two driving forces that shape ion movement across the membrane?

Chemical (concentration) gradient and electrical (voltage) gradient; their balance determines the net flux and the equilibrium potential.

What does Ex represent for an ion X?

The membrane potential at which there is no net movement of ion X across the membrane (the equilibrium potential for that ion).

What is the form of the Nernst equation for a monovalent ion?

Eion = (61 mV / z) log([out]/[in]); z is the ion's charge (valence).

Why are Nernst potentials useful for predictions in excitable cells?

They help predict the direction ions will move through channels and explain the behavior of resting/excitable membranes.

What is the Na+/K+ pump and its role?

An ATP-driven pump that maintains high intracellular K+ and low intracellular Na+ by actively transporting Na+ out and K+ in.

What is the relationship between Vm and Ex when a membrane is permeable to multiple ions?

Vm is a weighted average or compromise of the permeant ions' Ex values, depending on relative permeabilities.

Which ions are the four major ions discussed with their Ex values?

K+, Na+, Cl-, Ca2+.

List the Ex values for K+, Na+, Cl-, and Ca2+ as provided in the notes.

EK ≈ -87 to -90 mV; ENa ≈ +64 mV; ECl ≈ -89 mV; ECa ≈ +129 mV.

What is the meaning of the term 'electrochemical gradient' for an ion?

The driving force on an ion equals Vm - Ex; positive indicates outward tendency, negative indicates inward tendency.

What is implied by the statement 'Fixed anions'?

Intracellular fixed anions contribute to the negative resting potential and do not cross the membrane.

What happens when Vm equals Ex for a particular ion?

There is no net flux of that ion; the ion is at electrochemical equilibrium.

What happens to RMP if the membrane becomes more permeable to a different ion?

RMP shifts to be closer to that ion's Ex, since that ion's conductance dominates.

Why do ions like K+ and Cl- push the cell toward a more negative interior while Na+ and Ca2+ push toward a more positive interior?

Because of the direction of their electrochemical gradients: K+ and Cl- tend to make the inside negative, while Na+ and Ca2+ tend to make it more positive.