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Resting Membrane Potential Simulation

– Section 4 –

Determining the RMP Value

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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.

Voltmeter measuring the resting membrane potential of an excitable cell

Which Ions Most Influence the RMP?

The resting membrane potential is influenced by the contributions of K+, Na+, and Clions, 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)

2. At this potential, in which direction is the net movement of K+ ions?

3. Based on the factors considered in the simulation, is the concentration of K+ ions higher inside or outside the cell membrane?

4. In which net direction would K+ ions cross the cell membrane if a less negative membrane potential occurs?

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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)

2. At this potential, in which direction is the net movement of Na+ ions?

3. Based on the factors considered in the simulation, is the concentration of Na+ ions higher inside or outside the cell membrane?

4. In which net direction would Na+ ions cross the cell membrane if a less positive membrane potential occurs?

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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 Clequilibrium 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)

2. At this potential, in which direction is the net movement of Clions?

3. Based on the factors considered in the simulation, is the concentration of Clions higher inside or outside the cell membrane?

4. In which net direction would Cl ions cross the cell membrane if a less negative membrane potential occurs?

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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)

2. What is the calculated equilibrium potential for K+ ions?

3. If the cell membrane equals the K+ equilibrium potential, would Naions tend to enter or exit the cell?

4. What factor would restrict the movement of the Na+ ions?

5. How would the net movement of Na+ ions affect the membrane potential?

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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)

2. How does the above value compare to the membrane potential produced if only K+ and Na+ ions are considered?

3. Does adding Cl–  ions appear to have a significant or limited impact on the resting membrane potential?

How is chloride’s impact on the resting membrane potential affected by its equilibrium potential and membrane permeability?

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