resting potential

What is the resting membrane potential?

The electrical potential difference across the neuronal membrane when the neuron is not actively signalling.

What is the typical resting membrane potential of a neuron?

Approximately -70 mV (often measured between -65 and -70 mV).

Why is the resting membrane potential negative?

There is a slight excess of negative charge inside the neuron relative to the outside.

What is measured when recording membrane potential?

The potential difference between the inside and outside of the cell.

What membrane potential is recorded when both electrodes are outside the cell?

0 mV.

What happens to the membrane potential when a recording electrode enters a neuron?

It becomes negative, revealing the resting membrane potential.

Why is the resting membrane potential essential for life?

It provides the electrochemical conditions necessary for neuronal signalling and action potentials.

What is an electrical gradient?

A difference in charge across space that produces an electrical force on ions.

How do negative ions move in an electrical gradient?

Towards regions of relative positivity.

How do positive ions move in an electrical gradient?

Towards regions of relative negativity.

What is a concentration gradient?

A difference in the concentration of a substance between two regions.

How do ions move down a concentration gradient?

From an area of high concentration to an area of low concentration.

What two forces determine ion movement across neuronal membranes?

Electrical gradients and concentration gradients.

Can ions freely cross a lipid bilayer without ion channels?

No.

What allows ions to cross neuronal membranes?

Ion channels and ion pumps.

What is an ion pump?

A membrane protein that actively transports ions against their concentration gradient using energy.

What is the energy source used by ion pumps?

ATP.

Do ion pumps move ions with or against concentration gradients?

Against concentration gradients.

What is the main function of ion pumps?

To create and maintain ion concentration gradients.

What is an ion channel?

A membrane protein containing a pore that allows ions to diffuse down electrochemical gradients.

Do ion channels require ATP to move ions?

No.

What determines the direction of ion flow through a channel?

The electrochemical gradient acting on the ion.

What is selective permeability?

The membrane being more permeable to some ions than others.

What are the three main ways ion channels can open?

Ligand binding, voltage changes, and mechanical forces.

What is a ligand-gated channel?

A channel opened by binding of a chemical messenger.

What is a voltage-gated channel?

A channel opened by changes in membrane potential.

What is a mechanically gated channel?

A channel opened by physical deformation such as stretch.

What is the extracellular concentration of Na+ at rest?

Approximately 150 mM.

What is the intracellular concentration of Na+ at rest?

Approximately 15 mM.

What is the extracellular concentration of K+ at rest?

Approximately 4 mM.

What is the intracellular concentration of K+ at rest?

Approximately 140 mM.

Which ion is much more permeable than Na+ at rest?

K+.

How much greater is K+ permeability than Na+ permeability at rest?

Approximately 50-75 times greater.

What intracellular ion contributes significant negative charge but cannot cross the membrane?

Large negatively charged proteins.

What are the four factors contributing to resting membrane potential?

Intracellular proteins, Na+/K+ pump, K+ ions, and Na+ ions.

How do intracellular proteins contribute to resting membrane potential?

They are negatively charged and trapped inside the cell.

Why can't intracellular proteins leave the neuron?

They are too large to cross the membrane.

What is the Na+/K+ pump?

An ATP-dependent transporter that moves Na+ out and K+ into the cell.

How many Na+ ions are moved by the Na+/K+ pump per cycle?

3 Na+ out.

How many K+ ions are moved by the Na+/K+ pump per cycle?

2 K+ in.

Why does the Na+/K+ pump make the inside more negative?

One more positive charge leaves than enters.

What is the net charge movement of the Na+/K+ pump?

Net loss of one positive charge from the cell.

Which ion has the greatest influence on resting membrane potential?

K+.

Why does K+ have the greatest influence on resting membrane potential?

The membrane is highly permeable to K+ at rest.

What force drives K+ out of the cell?

The concentration gradient.

What force pulls K+ back into the cell?

The electrical gradient.

What is the equilibrium potential for an ion?

The membrane potential at which electrical and concentration gradients exactly balance.

What symbol is used for equilibrium potential?

Eion.

What is the equilibrium potential of potassium called?

EK.

Approximately what is EK?

Approximately -80 mV.

Why is the resting membrane potential close to EK?

The membrane is predominantly permeable to K+.

Does Na+ contribute to resting membrane potential?

Yes, but only slightly.

Why is Na+ influence on resting potential small?

The membrane has low permeability to Na+ at rest.

What direction does Na+ tend to move at rest?

Into the cell.

What effect does Na+ influx have on membrane potential?

Makes it slightly less negative.

What is the Nernst equation used to calculate?

The equilibrium potential of a single ion.

What does the Nernst equation take into account?

Ion concentration gradient across the membrane.

Can the Nernst equation accurately predict resting membrane potential?

No.

Why can't the Nernst equation accurately predict resting membrane potential?

It only considers one ion at a time.

Which equation is used to calculate membrane potential considering multiple ions?

The Goldman-Hodgkin-Katz (GHK) equation.

What does the GHK equation calculate?

The membrane potential (Vm).

What additional factor does the GHK equation include beyond concentration gradients?

Relative membrane permeability of ions.

What symbol represents membrane potential?

Vm.

What symbol represents permeability?

P.

Why is resting membrane potential not exactly equal to EK?

Because Na+ also contributes to Vm.

What happens to K+ current if Vm equals EK?

K+ current stops because there is no driving force.

What is meant by driving force?

The difference between membrane potential and an ion's equilibrium potential.

What is potassium conductance?

A measure of how easily K+ moves through open K+ channels.

What symbol represents potassium conductance?

gK.

What is the equation for potassium current?

IK = gK(Vm − EK).

What creates the ion concentration gradients needed for resting potential?

Ion pumps, especially the Na+/K+ pump.

Why is K+ permeability high at rest?

Because many resting K+ channels are open.

Why is Na+ permeability low at rest?

Few Na+ channels are open at rest.

True or False: The Na+/K+ pump moves 3 Na+ into the cell and 2 K+ out.

False.

True or False: The Nernst equation predicts resting membrane potential.

False.

True or False: Na+ moves freely across the membrane at rest.

False.

True or False: Large intracellular proteins contribute to membrane negativity.

True.

Which contributes more to resting membrane potential: Na+ or K+?

K+.

Which ion has the highest intracellular concentration?

K+.

Which ion has the highest extracellular concentration?

Na+.

What are the key determinants of resting membrane potential often summarised in exams?

Na+/K+ pump, high K+ permeability, low Na+ permeability, and trapped intracellular proteins.