Umkehrpotenziale

Umkehrpotenziale, translated as "reversal potentials," are a fundamental concept in electrophysiology, particularly when studying excitable cells like neurons and muscle cells. A reversal potential for a specific ion species is the membrane potential at which the net flow of that ion across the cell membrane becomes zero. This occurs when the electrical driving force acting on the ion exactly balances the chemical concentration gradient that drives its movement.

The Nernst equation is used to calculate the reversal potential for a single ion species. It takes into account the ion's concentration gradient across the membrane and the temperature. For a typical mammalian neuron, the reversal potential for potassium (E_K) is around -90 mV, and for sodium (E_Na) it is around +60 mV. The resting membrane potential of a cell is a weighted average of the reversal potentials of the ions that can cross the membrane, with the weighting determined by the relative permeability of the membrane to each ion.

Changes in ion concentrations, such as those occurring during physiological processes or in pathological conditions, will alter the reversal potentials. For example, an increase in extracellular potassium concentration will make the reversal potential for potassium more positive, and consequently, the resting membrane potential will also shift towards this more positive value. Understanding reversal potentials is crucial for comprehending how changes in ion flux affect membrane potential and cellular excitability.