testing testing testing okay one of the most difficult parts of this chapter is the action potential because it usually conjur up many nightmares for students because it can be quite a confusing thing to explain Action potentials or nerve impulse so first thing first let's talk about the let's do a bit of a brief introduction what exactly are action potentials and nerve impulse for the purpose of this video anytime I use the word action potential nerve impulse or electrical impulse they all mean the same thing by the way uh the action potential nerve impulse or electrical impulse are just terms used to describe the signal that is traveling along the neuron so don't worry about that I've mentioned this before look at the it's represented in those arrows where the travel from the sensory neuron to the relay neuron to the Moto neuron it also implies that if you can see this particular diagram here the action potential is traveling um along the axon right what does that signal or that action potential or that nerve impulse look like you know we have to try to physically explain what exactly is this action potential all about it's not just good enough to say oh Action potentials are just these things that travel along the neuron we need to know what's going on at the neuron level so like uh what I'm drawing here is as you can see the axon here now commonly when I ask my students to explain a nerve impulse or action potential they will say especially students who have done a bit of physics they will say um well maybe electrical impulse nerve impulse action potential might be the same as electricity so perhaps it is electrons moving along the Exxon or along the neuron and while that is a good attempt at an explanation that is not exactly what's going on at all because Action potentials nerve impulse or electrical impulse are not electrons moving along the neuron so if they are not electrons moving along the neuron what exactly are they well let's talk about it so before I explain it in detail I'm going going to give you the textbook definition for action potential and the textbook definition for action potential is as follows Action potentials or nerve impulses or electrical impulse by the way are defined as rapid change in the electrical charge distribution across a cell surface membrane now if you read that statement and you go huh what like can you slow down like what the hell does that mean you are not alone okay it's not an it it's not like oh students immediately go ah okay now I understand it completely if you are if you totally understand what I just said 90% of the time you're probably lying okay and it's okay A lot of my students will pretend that they understand and I'll tell them do you actually understand and I'll ask them do you actually understand it and they'll go no okay I don't um so don't worry about it so we are going to break everything down into its fundamental parts and then we'll explain it bit by bit and then we'll join it back together so I'm just highlighting rapid change electrical charge distribution and cell surface membrane now along the axon what cell surface membrane are we talking about by the way so imagine this Moto neuron and this axon here and I'm just showing you the direction of the electrical impulse they're just moving towards the right side now let's focus on the cell surface membrane first where exactly is the cell surface membrane remember a neuron is a cell of course they have cell surface membrane so just drawing part of the axon here you can see the phospholipid by layer and the blue color part represents the inside of the axon so whatever I'm circling in the Exxon represents that magnified image right there so that's the cell surface membrane but I'm going to simplify it and just going to put like a single you know purple line on each side that represents the cell surface membrane A to B just represents A's on the left side of the axon which I'm circling in green and B is on the right side of the axon which is I'm I'm circling that in blue for example so I'm just trying to say that the signal has to be sent from A to B so now we understand the cell surface membrane that's good the second thing we have to understand is the electrical charge distribution now what exactly does that mean now if you notice I'm putting negative symbols inside the axon and I'm putting positive symbols outside the axon this implies that the outside has a more positive charge and the inside has a less positive charge or more negative charge that positive and negative charges are separated by the cell surface membrane now I want you to understand you don't need to memorize this part but what that positive and negative charge actually means is as follows the electrical charge distribution across the cell surface membrane is affected by ions by the way examples as I'm drawing out here you can see the axon uh the blue color is the inside of the axon those orange color dots represent posi postively charged ions now examples of positively charged ions will be things like sodium ions and potassium ions right they give out positive charges so as an example here if you see if you notice in this diagram the concentration of the ions inside the axon and outside the axon are almost the same so there is not much of an electrical charge difference between the two areas now if we were to push out more of the ions out of the axon we notice that there is a higher positive charge or higher concentration of positive ions outside the cell and it's lower inside the cell or inside the axon in this diagram therefore to make life simpler for our cells instead of writing the word higher positive charge outside lower positive charge inside it's too much of a hassle we just simply represent it with by using a positive symbol outside and a negative symbol inside that's basically what it is the positive and negative symbol implies that there is just a higher voltage outside and a lower voltage inside this is known as the electrical charge distribution across the cell membrane also referred to as membrane potentials and they are measured in volts and we will be talking about this further in detail in the next video so I just need you to understand this part of the video first okay so that will help make life easier when we are studying resting membrane potential and search the other important thing I want you to understand is when you look at this axon it is not sending any signals yet or they are not sending any action potentials along the axon as of yet okay so the point I'm just trying to make over here is before it's able to send any action potentials from A to B it first has to make that electrical charge distribution where the outside is more positive or it has a higher charge and the inside has to be negative or it has a lower charge that is first called the electrical charge distribution if it doesn't have this action potentials or nerve impulses cannot be sent at all okay so this is most exons before they are able to send any impulse they first have to create that electrical charge distribution first now remember I told you that action potential is a rapid change in the electrical charge distribution for example let's say I want to send the signal from A to B suddenly what actually happens is I just want you to see the highlighted part what exactly happens to the highlighted part by the way at a the charge flips what do I mean by the charge flips now the inside is positive and the outside is negative that is called a rapid change and it happens extremely quickly so the rapid change in electrical charge distribution happens at Point a or nearer to towards a now what is happening here is as follows where Suddenly at the next instant is the same it's the same xon by the way but I want you to see what happens in the next diagram in the next diagram the next part of the Exxon the charge flips where the inside is positive and the outside is negative but look at the previous area what happens to the previous area it goes back to normal right so the next part under goes a rapid change and then what actually happens after that the next next part and then the next part and then the next part and then the next part basically until it reaches B that is actually referred to as the action potential by the way that is what we actually have to understand about the rapid change so the action potential are not electrons traveling it's just basically the charge along the cell surface membrane changing the charge flips first it flips on the left side at a and then it flips flips flips flips flips flips all the way to B but it doesn't remain and and you also have to understand once it flips it has to go back to normal I use the word flip but that's not the correct word to use by the way so I will explain that further in detail but the point I'm just trying to make is the change is rapid where the inside becomes positive for just one instant and then it goes back to normal and then the next area under goes the same change the charge distribution changes and then the next part it just continuously happens now if you're still not sure what you must first understand is the axon for the Exxon to send a signal it must have an electrical charge distribution also referred to as membrane potential where the inside has to be represented with negative and the outside has to be positive where the inside has a lower charge and the outside of the axon has a higher charge good that's called the electrical charge distribution along the cell surface membrane and then what happens when a gets stimulated we want to send the signal from A to B so when a a gets stimulated to send the signal the charge nearer to a under goes a rapid change where the inside becomes positive and the outside becomes negative and then what happens the next area under goes a rapid change good but the previous area the first one returns back to normal that's called the rapid change as well okay and then what happens next same thing okay and then the same thing until it reaches B that is called action potential but of course you might be thinking what is causing this positive what's causing this negative uh to happen uh why is it moving why is the charge changing from one area to another we will talk about that more in the next video