Theoretically, a recognized member of the modern state system possessing formal sovereignty and occupied by a people who see themselves as a single, united nation. Most nations and states aspire to parlance, nation-state is used as a synonym for country or state.
In biology, depolarization is a decrease in the absolute value of a cell's membrane potential. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations.
This is caused by a rapid but transient change in the permeability of the cell membrane to both sodium and potassium ions. Depolarization is caused by a rapid influx of sodium ions into the nerve cell which disrupts the charge gradient across the membrane.