sometimes the how would they ask the question is they would show you this graph okay and this graph is quite important so to look at this particular graph here this graph will explain to us the changes in the membrane potential of the Exxon over a period of time what do I mean by that so we are just taking one part of the xxon by the way we are not taking the entire xxon okay now I'm just and the y-axis of the graph is the membrane potential and the x-axis is time and I'm just drawing out as you can see here the the purple color blue the purple color dot at the left is the sodium potassium pump uh the orange color one in the middle is the voltage gated sodium ion Channel and the green color one on the right is the uh voltage gated potassium ion Channel at first can this axon send an Impulse no this axon cannot send an Impulse or it cannot generate the action potential why not because it doesn't have a potential difference okay it needs to First create and maintain a resting membrane potential so how does it create create and maintain the resting membrane potential it uses ATP to power the pump and the pump will transport out three sodium ions and transporting two potassium ions continuously until it makes the voltage inside lower and the voltage outside higher to -70 molts this is referred to as the resting membrane potential so that's still normal but when a stimulus is given it causes the as you can see that the voltage gated sodium ion Channel opens so what happens in this case over here sodium ions Rush In from a higher concentration outside to lower concentration inside thus it causes the membrane potential inside to become more positive because it's getting more sodium ions right so when it gets more sodium ions in this case the charge the it becomes more positive inside compared to outside so therefore the charge flips okay and this is depolarization by the way so at positive 30 MTS voltage gated sodium ion channels close and voltage gated potassium ion channels open so in this case go back over here to the resting membrane potential and just circling it there because we actively transported potassium ions in the inside had a higher concentration of potassium ions and also it had a lower concentration of potassium ions outside so during this point let's focus here at positive 30 MTS the voltage G potassium ion channels open they only open at posi 30 by the way so potassium ion rushes out therefore the inside now is losing positive ions the outside is becoming more positive that's why the inside as the inside loses more positive ions they're losing the ions right they become more negative that's why the membrane potential goes down again so In This Moment over here the outside becomes more positive okay this is repolarization so as you can see s pottassium ion rushes out okay the cell is losing more positive ion so the inside becomes more negative it veers back into its negative uh boundaries and therefore it reaches about it reaches about 8078 to 80 MTS okay so at this moment of time when it reaches here the voltage gated potassium ion channels will close from point number three to point number four is repolarization that's basically what happens but as you can see here there's a pink color line over here that pink color line is just basically time taken to return back to the resting membrane potential and that period is known as the refractory period for now all you have to know about the refractory period is the Exxon is unresponsive to any stimulus which means to say if you were to give a stimulus the axon will not generate an action potential so as you can see here the part where I'm circling here that's the action potential by the way depolarization and repolarization this is the signal okay that is being sent along the Axon