so in the previous video we talked about what exactly the resting membrane potential is okay we looked at the structure of the axon and then I also mentioned that before we are able to send action potentials or electric nerve impulses the axon has to First create and maintain a resting membrane potential and how do we do that it is done by using the sodium ion potassium ion pump where when it receives ATP the pump will carry out active transport and every time it does its function it will transport out three sodium ions and transport in two potassium ions against the concentration gradient and thus it creates and also the inside of the axon has some negatively charged proteins to make the voltage inside more negative than the voltage outside that's how you create the resting membrane potential and the value of the resting membrane potential is -70 m FSE now resting membrane potentials May differ depending on species okay the next thing that is actually supposed to happen I told you was something to do with action potential and I said that the action potential has two parts where when a gets stimulated the charge will flip where inside becomes positive and the outside becomes negative but that only happens for a brief moment and then it returns back to normal that rapid change and returning back to normal is called the action potential and it's split into two stages depolarization and repolarization so we're going to look at that uh process in detail so depolarization is very simple now what exactly happens during depolarization it is basically when the membrane potential from neg 70 becomes positive 30 mols right so remember first again I'm just repeating myself again to create the resting membrane potential the pump has to work it receives ATP three sodium ions go out two potassium ions are pumped in I keep repeating myself because I need to drive this home because this is an extremely complicated chapter where a lot of things are happening right so we have with this process we have created the resting membrane potential as I've circled over there -70 Ms all good and remember I also told you by the pump during this process it creates a gradient where there is a higher sodium ion concentration outside lower sodium ion concentration inside and for potassium ions it's the opposite higher inside lower outside right so this has been done now remember also the pump is not the only thing that is found on the axon's cell surface membrane there were also two other things there was the voltage gated sodium ion channels and the voltage get at potassium ion channels right so for this process process over here we are only going to focus on the voltage gated sodium ion Channel first because we are talking about depolarization now during depolarization what exactly happens is as follows the axon gets stimulated and I just want you to see what happens when the axon gets stimulated the voltage gated sodium ion channels open now what is the consequence when the channel protein opens when the sodium ion channel protein opens you might be thinking hm I'm not so sure but look at the concentration of the sodium ion outside and inside the axon so it's quite obvious facilitated diffusion will happen where sodium ions will rush in so during depolarization the voltage gated sodium ion channels open and the sodium ions rush into the axon why do they rush into the axon because they're rushing down the concentration gradient from high to low that's how they're supposed to work now as sodium ion continues going in the Insight starts to become a bit more positive right because sodium ion is a positive ion so from - 70 Ms it becomes -50 and as more sodium ions keeps going in it goes up to positive 30 molts that's how you achieve that membrane potential of positive 30 m Vols right there because sodium ions rushed into the axon and remember the sodium ion channel is a voltage gated channel right and and the reason why it's important is because and of course when voltage what does voltage gated mean voltage gated means it opens and closes at specific voltages when the the channel when the voltage reaches positive 30 m volts which means the inside is more positive than the outside the channel will close the channel specifically closes at around positive 30 MTS and thus because the inside has a higher voltage than the outside the charge flips there you go that's how you get the positive symbols inside and the negative symbols outside simple as that so at 30 m volts at positive 30 MTS the voltage G sodium ion channels close and that's basically it okay so let's do this again okay so at first to create the resting membrane potential the pump will actively transport out three sodium ions and transport into potassium ions this creates the resting membrane potential where the inside has a lower voltage than the outside therefore inside is NE negative outside is positive and during depolarization what exactly happens the voltage gated sodium ion channels open due to the stimulus and sodium ions rush in down the concentration gradient the inside now has a higher voltage represented by positive inside and negative outside this is how depolarization works and of course without wasting time let's immediately go into repolarization what happens during repolarization ization the charge has to return back to normal but if you notice I put the value not at - 70 MTS at80 M volts so let's so it goes back where the charge flips back again where during depolarization positive inside negative outsite but during repolarization it flips back again because I told you action potential is a rapid change it happens for a very short amount of time right so how does that happen how does repolarization happen so remember let's do the entire damn thing again okay I know it's annoying but it helps okay how do we create the resting membrane potential we do it using the sodium ion pottassium ion pump active transport three sodium ion out two potassium ions in continuously and during depolarization the voltage gated sodium ion channels open so sodium ions rush in why do the sodium ions flush in because it's higher outside and lower inside that's what makes the charge inside more positive and the outside negative right where the inside is higher voltage anyway so that creates the positive 30 MTS now this is where we have to talk about the voltage gated potassium ion channel so this is where we introduced the third transport protein earlier as depolarization was happening the sodium ion channel was opened but the potassium ion channel was closed but the moment it reaches positive 30 MS what's supposed to happen by the way yes once the membrane reaches positive 30 Mt I told you that the voltage gated sodium ion Channel closes as you can see that so it has closed good but at positive 30 MTS also the voltage gated potassium ion channels open so what's the consequence if the voltage gated potassium ion channels open exactly compare the potassium ion concentration inside the axon and outside the axon the potassium ions are represented in those green triangles you notice that there is a higher potassium ion concentration in the axon and lower outside so potassium ions rush out and as potassium ion rushes out the axon loses positive ions and when the so the outside starts to become more positive and when the outside becomes more positive the inside is a lower voltage by comparison so it becomes negative and as potassium ions continue rushing out it becomes about 80 molts you don't have to memorize negative 80 MTS but you just have to know that in its attempt to return back to the resting potential it overshoots the resting potential so it goes beyond that and becomes more negative than it was supposed to be so it goes slightly beyond the resting potential and once it reaches about 80 MTS give or take the voltage gated potassium ion channels will then close and thus we are actually done with depolarization and repolarization if you're still not so sure let's do this again so remember at that section of the axon I told you that before we are supposed to send the impulse the inside has to be represented with a negative symbol outside is positive which means inside has a lower voltage - 70 molts how do we create that resting membrane potential that is created using the sodium ion potassium ion pump okay represented over here when the xon is stimulated the charge flips where the inside becomes more positive and the outside is NE negative how did that happen that was because the voltage gated sodium ion channels open and therefore sodium ion rushes into the cell down the concentration gradient this is known as depolarization and once it reaches positive 30 MTS the sodium ion Channel closes and the voltage gated potassium ion channels open and potassium ions rush out down the concentration gradient as well because the inside had a higher pottassium ion concentration and the outside is lower and the charge flips back okay becoming 80 MTS where the inside is now negative and the outside is positive by comparison this is how the action potential takes place the action potential basically consists of just depolarization and repolarization so I hope you understand that