If the Na/K pump were inhibited what effect would this have on the resting membrane potential?
Resting membrane potential is generally around -70mV. This is maintained by the Na-K pump, which pumps Na+ out and keeps K+ in. If the pump were inhibited, Na+ would diffuse into the cell and increase the membrane potential to a more positive number. If enough sodium enters the cell, the threshold potential may be reached at about -55mV, and an action potential would result. So, the simple answer is that the resting membrane potential would be more positive.
What effect would depolarizing the membrane have on the Na+ K+ pump?
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Normally our cell plasma membrane has difference in charge between the inside and outside due to difference of electrolyte concentration. Theses differences call polarization.Let’s say in polarization state, the outside of the membrane is positively charged and the inside of the membrane is negatively charged.Due to movement of electrolyte via plasma membrane, it will create the changes of charge outside and inside the cell.Depolarization is the state which the cell membrane change from positive to negative charged outside the cell and from negative to positive charge inside the cell.Repolarization is the state which the cell membrane change back it resting stat, mean from negative to positive charge outside the cell and from positive to negative charge inside the cell.
The potassium outflow hyperpolarizes the neuron by a normal process, in which the movement of positively charged K+ ions to the outside of the cell moves the interior-anchored voltage potential in the negative direction.The effect of increasing extracellular potassium works by a different mechanism, which is why it has a different effect. The increase of extracellular potassium has three mechanistic effects [1] that result in a sustained depolarized state:The normally present hyperpolarizing outflow of potassium (K+) is slowed down (due to a reduced potassium gradient); Less hyperpolarizing outflow is equivalent to depolarization, since there is a depolarizing inflow of sodium (Na+) that was not also slowed down by an equivalent increase in intracellular sodium. The result is a change in the equilibrium potential of the cell. [2]The increase in the membrane potential (slow depolarization) opens some of the sodium channels, which lets positive Na+ ions into the cell, further depolarizing it. [3]The slow depolarization causes partial Na+ channel inactivation to occur as well. This prevents the neuron from triggering a full action potential (extreme depolarization followed by extreme hyperpolarization). As a result, the cell remains in a slightly depolarized state but never fires. [3]------[1] Wikipedia on the mechanism of action for the toxic effect of extracellular potassium: Hyperkalemia [2] Wikipedia on "neural accommodation", the effect by which a slow depolarization puts the cell in a semi-depolarize state: Neural accommodation [3] Wikipedia on "equilibrium potential", the mechanism by which ion gradients determine the positive or negative voltage of the cell: Reversal potential
How does the NA+/K+ pump affect ion distribution in a neuron?
The NA+/K+ pump pumps sodium out of the neuron and potassium into it. This lowers the intracellular sodium concentration and raises the intracellular potassium concentration. From http://www.emc.maricopa.edu/faculty/fara... "The plasma membrane of neurons, like all other cells, has an unequal distribution of ions and electrical charges between the two sides of the membrane. The outside of the membrane has a positive charge, inside has a negative charge. This charge difference is a resting potential and is measured in millivolts. Passage of ions across the cell membrane passes the electrical charge along the cell. The voltage potential is -65mV (millivolts) of a cell at rest (resting potential). Resting potential results from differences between sodium and potassium positively charged ions and negatively charged ions in the cytoplasm. Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane. This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump. The sodium-potassium pump maintains this unequal concentration by actively transporting ions against their concentration gradients.
Why does increasing extracellular potassium depolarize neurons?
initially the cell has high concentration of k+ ion inside relative to outside and a high concentration of negatively charged macromolecules that cannot exit the cell by Diffusion due their massive size so the cell now is neutral (+charge=-charge) the polarization effect happens when k+ ions defuse down their concentration gradient to the outside due the presence of specialized k+ions channels so k+diffuses out when the concentration outside the cell is less than the inside leaving the cell with negative charges thus generating the negative action potential note : the Diffusion doesnt cause noticeable changes in the concentrations so concentration gradient stays the same but when the concentration outside the cell is more the k+ ions diffuse to the inside depolarising the cell
Increased extracellular potassium levels depolarizes cells?
A neuron that's not firing action potentials has a negative resting membrane potential as you mentioned. The resting potential is maintained by the Na+/K+ pump AND nonspecific leakage of K+ ions out of the cell. Molecules like to go DOWN their concentration gradient. If the Na+/K+ pump is pumping 3Na+ out, and 2K+ in, then that means that the concentration of K+ inside the cell is GREATER than the concentration of K+ outside the neuron because the Na+/K+ pump is an example of ACTIVE transport. So the active pump pumps K+ in, causing the concentration of K+ inside the cell to build up. This means that the unspecified leakage of K+ will cause K+ ions to leak OUT of the neuron. Now, if the concentration of K+ outside the cell is very high...it's very hard for the K+ to continue to randomly leak out. This will lead to a build-up of K+ ions inside the cell. An excess of positive charges inside the cell will lead to depolarization. Remember, depolarization is characterized by an increasing (more positive) membrane potential. So anything that contributes to positive charges in the cell will depolarize the cell.
Hi there. Well, that’s a tough question because there are a lot of variables involved. For example, the sodium-potassium pump moves three Na out for every two K it pumps in. That alone affects membrane potential by keeping more positive ions outside the membrane than inside, so more positive charge outside. It’s also true that the membrane is already more permeable to K than to Na (about 75 times more permeable), so that unequal diffusion of the ions has affects on membrane potential too. So the question is what affect equal changes in membrane permeability to both ions would have on their concentration gradients relative to one another and thus how that would affect membrane potential. This is a tricky question that I am not best qualified to answer. You might consider waiting for an answer from someone better versed in cellular physiology as I would hate to give you an incorrect interpretation.
I don't know if this answers your question directly but I think it may remove some confusion about the negative membrane of neurons. The problem I had was the thought that K+ causes for a negative membrane. Like James Byrne already told, there is a concentration gradient between K inside/outside Na inside/outside. Now assume a membrane with 0 mV as potential but with the same ion channels as a neuron.On the inside there is a lot of K+. On the outside a lot of Na+. The fluid in which Na + en K+ are soluted is however neutral. This is possible because there are negative proteins and molecules inside and a lot of Cl- outside the membrane. Remember that the membrane had the ion channels of a neuron. This means K+ can flow more freely than Na+. Now K+ flows from inside to outside because of the concentration gradation. The proteins inside can't efflux. So the inside turns more negative because of K+ leaving. Na+ can't move in cause their flow is blocked. So this is how efflux of K+ leads to a negative membrane. There is a balance between the forces pulling the K+ to the outside due to the concentration gradient and the forces pulling K+ into the cell due to electric gradient at -70mV. Exact the same principle happens during the repolarisation of a action potential. K+ flows outside while Na+ influx is again blocked.