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In ionic steady state, cells maintain different internal and external concentrations of various ionic species.[1]

Cells are said to be in a steady state, NOT in an equilibrium. This means that there is a differential distribution of ions on either side of the cell membrane - that is, the amount of ions either side is not equal and therefore a charge separation exists. However, ions move across the cell membrane and almost constantly maintain a resting membrane potential; this is known as 'steady state.'

In a steady state the cell must be continuously providing energy to maintain such state and that is why we refer to it as a dynamic equilibrium and not just static equilibrium. In a static equilibrium things are the way they are due to no energy appliance, i.e., no energy is required to put the system at such state. Thus we say an equilibrium state has the same low level energy its environment also has. Differently, in a steady state, if we stop providing energy to maintain such "non natural equilibrium" (more properly said dynamic equilibrium), the system will return to its normal equilibrium, which is the equilibrium properly said, where no energy is required.

In a cell, since there are constantly several ions trying to get in and out of the intracellular space, the cell must provide energy to maintain the proper ions concentrations, so it's able to function properly. But that is not the natural equilibrium it would be if such energy would cease to apply to maintain such different concentrations (like the energy expended in the Na+/K+ pump, pumping 3 cations Na+ out and 2 cations K+ into the cell). If such pump stops working, the cell would just be governed by diffusion and electrical forces (attraction and repulsion from ions), and since this requires no energy it would soon reach its own natural equilibrium with no energy necessary to maintain such concentrations. But although it does not require energy it is not adequate for our cell to work properly. For a proper working, our cell needs a different ion concentration, which requires energy and that a system where a lot happens all the time, pumping ions in and out all the time in a never ending process, consuming 2/3 of our brain energy and 1/3 of all the energy we consume. All this energy is to allow the Na+/K+ pump work and bring our cell to a proper specific ions concentrations, and now we are in a dynamic state or more simply called a steady state.


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