 hey welcome to physiology open resting membrane potential is the potential across a membrane with negativity inside the membrane and positivity outside its value we generally say as a minus 70 millivolt but does it same for all cells if it differs why is it different for different cells and how is it generated after all well generation of resting membrane potential requires three things one there should be difference in concentration of ions on two sides of the membrane so say this side we have four positive and four negative ions say potassium and chloride and this side we have these 10 positive and 10 negative ions again say potassium and negatively charged proteins but will this be sufficient see even with the difference in concentration of ions net charge on both sides is zero so actually there will be no potential difference so second requirement for generation of RMP is that membrane should be differentially permeable to ions means it should be permeable to some ions and not to others so actually membrane is permeable to potassium and impermeable to negatively charged proteins which are present inside the cell so there are actually certain channels known as leaky channels for potassium which are present on the membrane now because of this permeability and difference in concentration of ions potassium starts to move outside see potassium concentration is more inside right so concentration gradient is from inside to outside but because of its movement its concentration will start increasing outside isn't it now this movement causes an imbalance of positive and negative ions inside and outside now their numbers are not equal inside and outside so this will create a negativity inside and positivity outside so what happens despite the concentration gradient being there from inside to outside this side starts repelling the ions because of the developing positivity this is known as electrical gradient so because of concentration gradient the ion tends to move from inside to outside but due to electrical gradient they tend to move from outside to inside so with time concentration gradient keeps on decreasing due to increasing number of charges outside while electrical gradient keeps on increasing after some time a point comes when concentration gradient of the ion is balanced by the equal and opposite electrical gradient so at this point there will be no net movement of charges and due to difference in positive and negative charges on each side of the membrane there is a development of the potential across the membrane this process of development of potential due to unequal distribution of ions when membrane is differentially permeable to ions is known as Gibbs-Johnnon equilibrium which we have discussed in another video in detail I have given the link for this in description section below anyways so till now we discuss two requirements for development of potential there should be concentration difference of ions across two sides of membrane and the membrane should be selectively permeable to ions now here we are talking about single ion that is potassium whose movement is causing potential development now the potential act which ions concentration gradient is balanced by its electrical gradient so that no net movement of charges occurs is known as equilibrium potential for that ion and this equilibrium potential can be determined by Nernst equation Nernst equation states that equilibrium potential for an ion is equal to RT by Fz log concentration of ion outside divided by concentration of ion inside the membrane where R is gas constant T is absolute temperature F is Faraday number and Z is valency of ions I will not go into the maths of all these but instead we will simplify the equation we will solve this value it comes to minus 61 log concentration inside divided by the concentration outside and if you are talking about negatively charge ion we just invert this here so it becomes minus 61 log concentration outside divided by concentration inside or in some books you will see that this minus sign there removes but keep the concentration ratio as the original one so both are correct ways but we will stick to this inverted concentration ratios because this will help us in understanding another equation Goldman-Hodgkin-Katz equation which we will soon discuss so let's now solve the equation for potassium ion because that's the ion we have been talking about till now so for potassium ion intracellular concentration is 140 mill equivalence per liter while extracellular concentration is 4 mill equivalence per liter so let us put these values here in the equation and see how much our equilibrium potential is on solving it comes to minus 94 millivolts but our RMP which we stated in the beginning is we said the minus 70 millivolts so that means there are other things also playing a role in RMP generation well a cell does not be exactly like what we discussed till now instead there are many ions involved simultaneously so at rest membrane is more permeable to potassium but it is also permeable to sodium chloride but much lesser than potassium so that means all these ions contribute to RMP so now how to determine RMP with Nernst equation we have already said that Nernst equation is used for single ion secondly Nernst equation assumes that membrane is fully permeable to that ion but here we are saying that membrane permeability to different ion varies it's not fully permeable to all ions so what will determine the value of resting membrane potential well all ions will have some role depending on the concentration difference inside and outside and the permeability of the membrane to that ions so let's see how much will be the equilibrium potential for sodium only with the Nernst equation extracellular sodium is 140 millivolts per liter and intracellular it is 14 millivolts per liter so we'll just replace the values and it comes to plus 61 millivolts so RMP should be somewhere in between these values that is potassium and sodium equilibrium potentials depending on membrane permeability to sodium and potassium at rest so RMP cannot be determined by Nernst equation if we consider more than one ion instead for that we use Coleman-Hodgkin-Katz equation now GHK equation is something like this don't get afraid by looking at the equation in a minute I will simplify it for you see this equation is simply an extension of Nernst equation this portion if you see isn't it same as Nernst equation but here in this equation permeability of the membrane is also included so this we can say is Nernst equation with permeability of the membrane for that ion included and if we look further after plus sign it just adds this factor again for other positive ion and if it is a negative ion this concentration ratio is reversed this we have discussed in Nernst equation isn't it that's all that is GHK equation so when many ions are involved we determine RMP by GHK equation okay now can you tell that why different cells have a different RMP well different cells have a different concentration gradient for different ions and also the membrane permeability of the different cells varies for different ions so obviously if you put the values in GHK equation RMP will come different for different cells isn't it okay now apart from this one very important role is also played by sodium potassium 80 pace firstly sodium potassium 80 pace throws out three sodium ions and brings in two potassium ions so there is a movement of unequal number of ions more positive ions are going out than those are coming in so it is adding negativity inside the membrane of about minus four millivolts but that is not that much important role in RMP generation but you know that for the cells which are active that is that respond to an stimulus say suppose not with each action potential there are changes in sodium and potassium concentrations now these concentrations are brought back to normal by sodium potassium 80 pace so this pump is very essential for maintaining the concentration difference of ions if it doesn't work within no time this ion gradient will be lost which we have seen is so important for resting membrane potential so in short we can say that gives on an equilibrium generates resting membrane potential while sodium potassium 80 pace maintains it okay let's end the video with the most battling question which people have what will be the change in membrane potential if potassium concentration increases outside the membrane think about the question and put your answers and possible reason as comments below and we can discuss this question well thanks for watching the video if you liked it do like and share the video and don't forget to subscribe to the channel Physiology Open. 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