 Hi, let us solve some important questions on equilibrium potential and resting membrane potential. So, first question goes like this, a decrease in extracellular concentration of potassium causes switch off please. So, for solving this, we need to know about NERS equation which gives us the equilibrium potential of a particular ion. So, it goes like this equilibrium potential for a particular ion is equal to minus 61 log concentration of the ion inside divided by concentration of the ion outside. So, this is the simplified version where we have solved the equation, right? And just by knowing this simplified version, we can get the equilibrium potential for any ion, right? So, let us solve for potassium. So, how it will go minus 61 log concentration of ion inside normally is 140 milli equivalence per liter and concentration of ion outside is 4 milli equivalence per liter. Now, it goes like this, a decrease in extracellular concentration of potassium. So, that means the denominator we have to decrease. So, maybe we can make it 2, right? Before it was 4. So, before you see this value will come to 35 and now when the value becomes 2, it will come to 17, isn't it? So, this by decreasing extracellular concentration of potassium, it will get log 70 which obviously will be a higher value compared to log 35, right? And what we will get is basically minus 61 log 70. So, this will go towards more negative value, more negative value. So, that means it is going to lead to hyperpolarization. So, that is the answer. But in this question, it also says two different things that is increased excitability and decreased excitability. So, whenever the resting membrane potential decreases, which normally is close to the equilibrium potential of potassium, whenever it decreases, we will get decreased excitability because more potential change is required for the potential to reach to the threshold. So, in this case, two answers are there, hyperpolarization and decreased excitability. With the same logic, if there is increase in extracellular concentration of potassium, that is hyperkalemia if it occurs, then the answers would have been depolarization and increased excitability because in that case of this denominator will increase, okay? Say from 4 it can become 6, right? And this value will become less negative and when the potential becomes less negative, it is known as depolarization. With this, let us move on to the next question. What is the nurse potential for potassium? So, in physiological condition we are talking, so as I told you that again, same you have to put minus 61 log concentration inside by concentration outside and it comes to minus 61 log 35, okay? And the answer actually is minus 90 millivolts, the nurse potential for potassium is minus 90 millivolts. Third question, chloride concentration outside is 100 moles per liter and inside is 10 moles per liter or we can make it millimoles because in body it is in millimoles, right? Calculate its equilibrium potential. So, again you put what the nurse equation that is equilibrium potential is how much minus 61 log concentration inside by concentration outside. Now, for solving this question, you should remember one thing that actually this equation is simplified for a positive ion, okay? For a positive ion. When we consider negative ion, we have to change the signs, okay? So, either the equation will become as plus 61 log concentration inside divided by concentration outside or we can write it as minus 61 log and invert this part, okay? Concentration outside divided by concentration inside. Now, I use this equation based on how this divisibility is coming, right? If it is easy to divide inside by outside, okay? Then I use this equation otherwise I can use this equation. So, simply what you do is plus 61 log, here you see inside is how much? Inside is 10 millimoles and outside is 100, okay? So, here, okay, divisibility is okay only but there might be some questions in which it is difficult to divide, right? So, minus 61 log, here what we will do is 100 by 10, okay? Outside is 100. So, this comes as log 10. Log 10 is 1. So, answer becomes minus 61 millivolts. So, that is the equilibrium potential for chloride. So, I think you should remember this particular concept that for negative ion, either you invert the sign here and write the equation or invert this ratio. It is up to you. Five. Let's go to the next question. Identity is close to equilibrium potential of which ion? Well, you see, when we talk about a NERS equation, we are talking about equilibrium potential of a single ion but when we talk about resting membrane potential, actually many ions contribute to resting membrane potential and for determining the value of resting membrane potential, we use the GHK equation that is Goldman-Rochkin-Katz equation, right? Because this equation includes many ions. It includes sodium, potassium, fluoride and it also includes the permeability of the membrane to these ions because the membrane permeability actually changes, isn't it? So, at rest, you see that permeability of the membrane to sodium is almost nil. It is zero. So, this does not contribute to potential. On the other hand, the permeability of the membrane at rest is much, much higher for potassium due to the presence of leaky potassium channels. So, these potassium channels actually are open at rest and that is why the permeability of membrane to potassium is high and that is the reason that RMP is close to equilibrium potential of potassium ions. So, that is the answer. Okay, let's quickly move to next question. Genesis of resting membrane potential is due to all except. So, actually Genesis of resting membrane potential, if you see how it occurs, so suppose this is the cell membrane and this is the inside of the cell and here it is the outside of the cell. Very important for Genesis is presence of a non-diffusable ion. Okay. So, actually inside of the cell, there is proteins which are negative ions, right? These are non-diffusable ions and do not cross the membrane freely. And because of the presence of this non-diffusable ion, Gibbs-Tonnell equilibrium takes place leading to unequal distribution of ions on both sides of the membrane. So, potassium becomes more inside and chloride becomes more outside what we classically see in examples of Gibbs-Tonnell equilibrium, right? And this also leads to generation of potential because there is a gradient for ions to move and ions don't move only by the concentration gradient. They also move by means of the electrical gradient. So, when the concentration gradient becomes equal to the electrical gradient, then it causes generation of pristine membrane potential. So, in this, if you see membrane impermeability proteins, yes, it is required for Genesis of pristine membrane potential, Gibbs-Tonnell equilibrium definitely required. Then sodium potassium pump also has an important role because it maintains the concentration of sodium outside the cell and potassium inside the cell. Plus, it is an electrogenic pump. Sodium potassium is an electrogenic pump because it throws out three sodium ions, right, and brings in two potassium ions. So, basically it is throwing out one sodium ion extra and this contributes to little bit negativity inside of minus 4 millivolt. So, it also contributes to Genesis of pristine membrane potential. So, answer here is second one, voltage-gated potassium channels. Actually, it is for leaky channels which are important for Genesis of pristine membrane potential, leaky potassium channels. So, I hope with this, you will be able to solve the questions on NERS equation, very simplified manner you have to look at it and also what are the factors which are important for generation of pristine membrane potential. Thanks for watching the video. If you liked it, do press the like button, share the video with others and don't forget to subscribe to the channel Physiology Open.