The resting membrane potential (RMP) is the potential difference across the membrane of excitable cells such as nerve and muscle cells in the period between action potentials (at rest).

The RMP is established by DP's which result in concentration differences for various ions across the cell membrane which were established by active transport mechanisms.

Each permeant ion attempts to drive the membrane potential toward its own equilibrium potential.

Ions with the highest permeability or conductances at rest will make the greatest contribution to the RMP.

The RMP of the most excitable cells falls in the range of -70 to -80 mV.

The RMP is close to the EP for K+ and Cl- because the permeability to these ions at rest is high.

The RMP is far from the EP for Na+ and Ca2+ because the permeability to these ions at rest is low.

There is an equation for evaluating the contribution each ion makes to the membrane potential by using the chord conductance equation which weights the EP for each ion (Nernst) and it's relative conductance.

Ions with higher conductance drive the MP toward their EP and vice versa.

There is another approach called the Goldman equation which calculates using the contribution of each ion by relative permeability, not conductance.

We don't need to know the equation, so I'm not putting it here. You only need to know what the equation calculates.

<aside> ⚠️ *What role, if any, does the Na+-K+ ATPase play in creating the resting membrane potential?

Remember that the Na+-K+ ATPase pump pumps out three Na+ ions for every two K+ ions pumped in. Since the concentration gradient indirectly regulates the K+ concentration gradient which drives the MP toward the K+ EP. We can, therefore, say the ATPase plays a role in maintaining the gradient of K+ concentration gradient which establishes the RMP. Similarly, we can say the ATPase plays a role in maintaining the gradient of Na+ concentration.*

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