Depolarization is the act of neutralizing polarity. In biology this is related to cells and cell membranes in that it lessens the membrane potential to a less negative value. This can be caused or triggered by a number of events, but most often it is caused by an increase of sodium or calcium (or both). These triggering agents are often called 'cations'. In neurons or muscle cells, depolarization can cause an eletric impuse that is referred to as action potential.
