Resting Membrane Potential Simulation
– Section 4 –
Determining the RMP Value
Links to Other Sections
Measuring RMPs
Cations and anions surround the cell membranes of excitable cells, such as neurons and muscle cells.
Due to the distribution of these ions, charges develop on both sides of the membrane.
While excitable cells are at rest, the ions continue to move across the membrane, but their movement is balanced, resulting in no net gain or loss of charge.
The charges on either side of the cell membrane can be measured by placing a reference electrode outside the cell membrane and a recording electrode inside.
The charge difference between the two electrodes, the membrane potential, is measured in millivolts (mV) using a voltmeter.
When the charges on the inside and outside of the cell membrane differ, the measured membrane potential will be greater or less than 0 mV.
Which Ions Most Influence the RMP?
The resting membrane potential is influenced by the contributions of K+, Na+, and Cl– ions, and the outcome is like a tug-of-war between the equilibrium potentials of these three ions.
The ion with the highest membrane permeability will most impact the resting membrane potential.
How Ions Influence the RMP
What is the RMP if Only K+ Ions are Considered
If only K+ ions are considered, the resting membrane potential be the same as the K+ equilibrium potential.
An ion’s equilibrium potential is reached when the force generated by an opposing electrical gradient balances the ion’s concentration gradient. At equilibrium, ions still move across the membrane, but neither side has a net gain.
Analysis Questions
1. What is resting membrane potential if only K+ ions are considered? (Press the K+ in the simulation to determine the value)
The resting membrane potential equals approximately -95 mV, the equilibrium potential of K+.
2. At this potential, in which direction is the net movement of K+ ions?
Even though the ions are still moving across the cell membrane at equilibrium, there is no net gain of K+ ions on either side of the membrane.
3. Based on the factors considered in the simulation, is the concentration of K+ ions higher inside or outside the cell membrane?
The concentration of K+ ions is higher inside the cell.
4. In which net direction would K+ ions cross the cell membrane if a less negative membrane potential occurs?
The net movement of K+ ions would be out of the cell.
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What is the RMP if Only Na+ Ions are Considered
If only Na+ ions are considered, the resting membrane potential will be the same as the Na+ equilibrium potential.
Analysis Questions
1. What is resting membrane potential if only Na+ ions are considered (Press Na+ in the simulator to determine the RMP value)
The resting membrane potential equals approximately +65 mV, the equilibrium potential of Na+.
2. At this potential, in which direction is the net movement of Na+ ions?
Even though the ions are still moving across the cell membrane at equilibrium, there is no net gain of Na+ ions on either side of the membrane.
3. Based on the factors considered in the simulation, is the concentration of Na+ ions higher inside or outside the cell membrane?
The concentration of Na+ ions is higher inside the cell.
4. In which net direction would Na+ ions cross the cell membrane if a less positive membrane potential occurs?
The net movement of Na+ ions would be into the cell.
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What is the RMP if Only Cl– Ions are Considered
If only Cl– ions are considered, the resting membrane potential will be the same as the Cl–equilibrium potential.
Analysis Questions
1. What is resting membrane potential if only Na+ ions are considered (Press the Cl– in the simulation to determine the value)
The resting membrane potential equals approximately -65 mV, the equilibrium potential of Na+.
2. At this potential, in which direction is the net movement of Cl– ions?
Even though the ions are still moving across the cell membrane at equilibrium, there is no net gain of Cl– ions on either side of the membrane.
3. Based on the factors considered in the simulation, is the concentration of Cl– ions higher inside or outside the cell membrane?
The concentration of Cl– ions is higher outside the cell.
4. In which net direction would Cl– ions cross the cell membrane if a less negative membrane potential occurs?
The net movement of Cl– ions would be into the cell.
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What is the RMP if both K+ and Na+ Ions are Considered
If both ions are considered simultaneously, the outcome will be a weighted balance between their equilibrium potentials.
The ion with the highest membrane permeability will most impact the resting membrane potential.
Analysis Questions
1. What is membrane potential if both K+ and Na+ are considered? (Press K+ Na+ in the simulator to determine the RMP value)
The resting membrane potential equals approximately -72 mV, the equilibrium potential of Na+.
2. What is the calculated equilibrium potential for K+ ions?
The equilibrium potential for K+ ions is approximately -95 mV.
3. If the cell membrane equals the K+ equilibrium potential, would Na+ ions tend to enter or exit the cell?
Na+ ions would tend to enter the cell.
4. What factor would restrict the movement of the Na+ ions?
The cell membrane is much less permeable to Na+ ions than K+ ions.
5. How would the net movement of Na+ ions affect the membrane potential?
The small leakage of Na+ ions into the cell is sufficient to cause a modest depolarization, causing the resting membrane potential to move closer to -70 mV.
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What is the RMP if All Three Ions (K+, Na+, and Cl–) are Considered
Again, if all three ions are considered simultaneously, the outcome will be a weighted balance between their equilibrium potentials, which favors the ion with the highest membrane permeability.
Analysis Questions
1. What is membrane potential if K+, Na+, and Cl– ions are collectively considered? (Press K+ Na+ Cl– in the simulator to determine the RMP value)
The membrane potential is approximately -70 mV.
2. How does the above value compare to the membrane potential produced if only K+ and Na+ ions are considered?
The RMP produced by all three ions is slightly less negative than the RMP produced by K+ and Na+ ions.
3. Does adding Cl– ions appear to have a significant or limited impact on the resting membrane potential?
It seems to have a limited impact on the RMP.
How is chloride’s impact on the resting membrane potential affected by its equilibrium potential and membrane permeability?
The equilibrium potential for Cl– ions is approximately equal to the resting membrane potential established primarily by K+ and Na+ ions. Also, the cell membrane has a relatively low permeability to Cl– ions.
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