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| | Membrane potentials |
 | | Membrane potentials are determined primarily by three factors: 1) the concentration of ions on the inside and outside of the cell; 2) the permeability of the cell membrane to those ions (i.e., ion conductance); and 3) by the activity of electrogenic pumps (e.g., Na |
 | | At a resting membrane potential of -90 mV, there is a very large electrical and chemical driving force (-140 mV) acting upon external Na to cause these ions to diffuse into the cell. |
 | | However, to fully understand how multiple ions affect the membrane potential, and ultimately how the membrane potential changes during action potentials, it is necessary to learn how changes in membrane ion permeability, that is, changes in ion conductance, affect the membrane potential. |
| www.cvphysiology.com /Arrhythmias/A007.htm (765 words) |
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