Follow the direction in the lower right, black box for each of the Resting Membrane Potential (RMP) animations below.


 How do ions affect membrane potential?

Resting Membrane Potential (RMP) is the voltage (charge) difference across the cell membrane when the cell is at rest. 
RMP is a product of the distribution of charged particles (ions).

There are positively charged ions called cations (e.g., Na+, K+, Mg2+, Ca2+) and negatively charged ions called anions (e.g., Cl- and proteins that act as anions).

Do you remember how an atom becomes a cation or an anion?  If not, then see the general chemistry module.



The Na+/K+ Pump creates a concentration gradient by moving 3 Na+ out of the cell and 2 K+ into the cell.

Note the background color changes which indicate the concentration of these ions.  

Also note that the pump continues to move Na+ out of the cell even when more Na+ ions are present there.   In other words, Na+ is being pumped (and K+ in) against their concentration gradients.   

Because this pump is moving ions against their concentration gradients it requires energy in the form of ATP.  What kind of cell transport is this?


How do ion leak channels affect RMP?

The cell membrane contains protein channels, called leak channels that allow Na+ or K+ to leak down their concentration gradients.  Will Na+ tend to leak INTO or OUT OF the cell?  What about K+?

Cell membranes are considerably more permeable to K+ than to Na+ because they have many more K+ leak channels than Na+ leak channels.   

Do leak channels require ATP to move ions?   What kind of cell transport is this?


How does the cell function with leak channels and the Na+/K+ pump working?

The Na+/K+ pump moves Na+ out of the cell and K+ into the cell against their concentration gradients. The leak channels allow Na+ and K+ to move across the cell membrane down their gradients (from a high concentration toward a lower concentration). 

With the combined ion pumping and leakage of ions, the cell can maintain a stable resting membrane potential.


Why is the inside of the cell membrane more negative as compared to the outside?   


How do gated channels effect membrane potential?

Cell membranes also contain gated channels.  Gated channels can be opened or closed depending on conditions in the cell (e.g., pressure, voltage, presence of chemicals, etc).

 How does the cell's membrane potential change as Na+ channels are opened?  Why does Na+ move in that direction?

How does the cell's membrane potential changes as K+ channels are opened?   Why does K+ move in that direction?