<Ul> <Li> Panel 1 of the diagram shows a diagrammatic representation of a simple cell where a concentration gradient has already been established . This panel is drawn as if the membrane has no permeability to any ion . There is no membrane potential, because despite there being a concentration gradient for potassium, there is no net charge imbalance across the membrane . If the membrane were to become permeable to a type of ion that is more concentrated on one side of the membrane, then that ion would contribute to membrane voltage because the permeant ions would move across the membrane with net movement of that ion type down the concentration gradient . There would be net movement from the side of the membrane with a higher concentration of the ion to the side with lower concentration . Such a movement of one ion across the membrane would result in a net imbalance of charge across the membrane and a membrane potential . This is a common mechanism by which many cells establish a membrane potential . </Li> <Li> In panel 2 of the diagram, the cell membrane has been made permeable to potassium ions, but not the anions (An) inside the cell . These anions are mostly contributed by protein . There is energy stored in the potassium ion concentration gradient that can be converted into an electrical gradient when potassium (K) ions move out of the cell . Note that potassium ions can move across the membrane in both directions but by the purely statistical process that arises from the higher concentration of potassium ions inside the cell, there will be more potassium ions moving out of the cell . Because there is a higher concentration of potassium ions inside the cells, their random molecular motion is more likely to encounter the permeability pore (ion channel) than is the case for the potassium ions that are outside and at a lower concentration . An internal K is simply "more likely" to leave the cell than an extracellular K is to enter it . It is a matter of simple diffusion doing work by dissipating the concentration gradient . As potassium leaves the cell, it is leaving behind the anions . Therefore, a charge separation is developing as K leaves the cell . This charge separation creates a transmembrane voltage . This transmembrane voltage is the membrane potential . As potassium continues to leave the cell, separating more charges, the membrane potential will continue to grow . The length of the arrows (green indicating concentration gradient, red indicating voltage), represents the magnitude of potassium ion movement due to each form of energy . The direction of the arrow indicates the direction in which that particular force is applied . Thus, the building membrane voltage is an increasing force that acts counter to the tendency for net movement of potassium ions down the potassium concentration gradient . </Li> <Li> In Panel 3, the membrane voltage has grown to the extent that its "strength" now matches the concentration gradient's . Since these forces (which are applied to K) are now the same strength and oriented in opposite directions, the system is now in equilibrium . Put another way, the tendency of potassium to leave the cell by running down its concentration gradient is now matched by the tendency of the membrane voltage to pull potassium ions back into the cell . K continues to move across the membrane, but the rate at which it enters and leaves the cell are the same, thus, there is no net potassium current . Because the K is at equilibrium, membrane potential is stable, or "resting" (E). </Li> </Ul> <Li> Panel 1 of the diagram shows a diagrammatic representation of a simple cell where a concentration gradient has already been established . This panel is drawn as if the membrane has no permeability to any ion . There is no membrane potential, because despite there being a concentration gradient for potassium, there is no net charge imbalance across the membrane . If the membrane were to become permeable to a type of ion that is more concentrated on one side of the membrane, then that ion would contribute to membrane voltage because the permeant ions would move across the membrane with net movement of that ion type down the concentration gradient . There would be net movement from the side of the membrane with a higher concentration of the ion to the side with lower concentration . Such a movement of one ion across the membrane would result in a net imbalance of charge across the membrane and a membrane potential . This is a common mechanism by which many cells establish a membrane potential . </Li> <Li> In panel 2 of the diagram, the cell membrane has been made permeable to potassium ions, but not the anions (An) inside the cell . These anions are mostly contributed by protein . There is energy stored in the potassium ion concentration gradient that can be converted into an electrical gradient when potassium (K) ions move out of the cell . Note that potassium ions can move across the membrane in both directions but by the purely statistical process that arises from the higher concentration of potassium ions inside the cell, there will be more potassium ions moving out of the cell . Because there is a higher concentration of potassium ions inside the cells, their random molecular motion is more likely to encounter the permeability pore (ion channel) than is the case for the potassium ions that are outside and at a lower concentration . An internal K is simply "more likely" to leave the cell than an extracellular K is to enter it . It is a matter of simple diffusion doing work by dissipating the concentration gradient . As potassium leaves the cell, it is leaving behind the anions . Therefore, a charge separation is developing as K leaves the cell . This charge separation creates a transmembrane voltage . This transmembrane voltage is the membrane potential . As potassium continues to leave the cell, separating more charges, the membrane potential will continue to grow . The length of the arrows (green indicating concentration gradient, red indicating voltage), represents the magnitude of potassium ion movement due to each form of energy . The direction of the arrow indicates the direction in which that particular force is applied . Thus, the building membrane voltage is an increasing force that acts counter to the tendency for net movement of potassium ions down the potassium concentration gradient . </Li> <Li> In Panel 3, the membrane voltage has grown to the extent that its "strength" now matches the concentration gradient's . Since these forces (which are applied to K) are now the same strength and oriented in opposite directions, the system is now in equilibrium . Put another way, the tendency of potassium to leave the cell by running down its concentration gradient is now matched by the tendency of the membrane voltage to pull potassium ions back into the cell . K continues to move across the membrane, but the rate at which it enters and leaves the cell are the same, thus, there is no net potassium current . Because the K is at equilibrium, membrane potential is stable, or "resting" (E). </Li>

What effect does the na+/k+ pump have on the resting membrane potential of a neuron