BIOELECTRICITY

 

Electrical Potential

A cell derives its electrical properties mostly from the electrical properties of its membrane.

A membrane, in turn, acquires its properties from its lipids and proteins, such as ion channels and transporters.

An electrical potential difference exists between the interior and exterior of cells.

Charged particles gain or lose energy as they move between places of different electrical potential, just as an object with mass moves "up" or "down" between points of different gravitational potential.

Electrical potential differences are usually denoted as V or Delta-V and measured in volts; therefore, potential is also termed voltage.

The potential difference across a cell relates the potential of the cell's interior to that of the external solution, which, according to the commonly accepted convention, is zero.

Potential differences between two points that are separated by an insulator are larger than the differences between these points separated by a conductor.

`Thus, the lipid membrane, which is a good insulator, has an electrical potential difference across it. This potential difference ("transmembrane potential") amounts to less than 0.1 V, typically 30 to 90 mV in most animal cells, but can be as much as 150 - 200 mV in plant cells.

On the other hand, the salt-rich solutions of the cytoplasm and blood are fairly good conductors, and there are usually very small differences at steady state (rarely more than a few millivolts) between any two points within a cell's cytoplasm or within the extracellular solution.