right so for this particular part of the video what we're going to be looking at is the function of the milein sheet in transmitting action potential or Nerf impulse now just a bit of revision we've covered the mine sheet before in a previous video where we talked about the structure and I told you that the milein sheet are just these particular structures made out of something called the Schwan cell and the Schwan cell wraps around the axon to form the covering of the mine sheet and certain parts of the axon which are not melinated are referred to as something called the nodes of Runway now I'm just drawing it back over here and as you can see here certain parts are mated and certain parts are not melinated if we were to magnify if we were to just zoom in a little bit here I want you to see the concentration or the amount of sodium ion channels along the a on again we are just focusing on the sodium ion channels um we are not focusing on the sodium ion potassium ion pump or the uh potassium ion channels not because they don't exist they do exist but the sodium ion channels are just the core Focus over here so for this part what I want you to see is I want you to notice that for the part of the axon where it's melinated you notice that there are less channels or less sodium ion channels and for the nodes of runva which are not melinated they have more sodium ion channels and also by the way the milein sheet provides an area of electrical insulation what I mean by electrical insulation is the ions outside the axon will have great difficulty trying to diffuse into the axon because the mine layer is made up of predominantly lipids so lipids are mostly nonpolar I'm not saying that there phospholipids can be polar as well uh but the lipids are predominantly nonpolar so they do repel the ions away and even if they don't repel the ions away the lack of channels make it difficult for the ions to either diffuse into the axon or diffuse out of the axon but conversely in the nodes of vanv because they don't have those insulation and they have more channels the ions will have an easier time diffusing into the Axon or diffusing out of the axon depending on the concentration gradient so you might be thinking okay big whoop why do I care so let me just write it back again the milein sheet provides an area of electrical insulation so therefore the ions cannot pass through and the nodes of run V have no electrical insulation so ions can pass through some students will say oh parts of the axon which are melinated or half the mine sheet are less permeable to ions and the nodes of run are more permeable to ions that is a valid statement that you can also make so what's the big deal why why do we have to care about this insulation or such the reason is because the function of the milein sheet is to speed up the action potential now some students will immediately go how does that happen how because I just mentioned that the milein sheet prevents ions from passing through so in any so some students will say shouldn't it actually reduce the action potentials right it shouldn't speed up the action potentials so let's look at it now what I'm drawing over here is the axon I'm drawing out two different axons by the way it's not a time lapse okay two different two separate axons and the axon at the top is unmated and the axon at the bottom is mated as you can see the Aon the the axon at the bottom has those mine sheets just those parts where I've highlighted in beige is that beige beige maroon no not maroon definitely not maroon beige or brown Peach whatever okay right so let's look at the unmated axon now for the unmarinated axon if a stimulus is given to that section of the axon what happens is the first section the first part of the axon will undergo depolarization where sodium ions diffuse into the Axon so the membrane fully depolarizes assuming that it reaches the threshold potential by the way and when one section depolarizes it produces a local circuit local circuit will cause the next section sodium ion channels to open and sodium ions Rush In And therefore that next section will also depolarize again it produces another local circuit which causes the next section sodium ion channels to open so sodium rushes in which causes the next section to also depolarize and repeat at nauseum until all the way towards the end of the axon we've studied this in the previous chapter where local circuits produced in the axon will cause the next section to depolarize which causes the next section to depolarize and you know so on and so forth okay fine so we've covered that that's normal stuff but let's look at the melinated axon so I'm just going to zoom in a little bit over here when we give the stimulus to the melinated axon the first part same thing the sodium ion channels open so sodium ion veres in the membrane depolarizes so far so good everything is the same but the problem here is local circuits that are produced which means the sodium ions inside the axon they will diffuse into the next section but when they diffuse into the next section they are supposed to stimulate the sodium ion channels in the section that I'm circling over there there but I told you in this part of the video I said that in the melinated part of the axon there are a lack of channels they may have some channels but it's very few it's almost insignificant and even if the channels open sodium ions cannot diffuse in the reason why is because the mine sheet provides an electrical insulation so that part of the membrane doesn't depolarize but the local circuit will just move forward which causes that section of the axon which has a lot of sodium ion channels as I'm drawing out here and those sodium ion channels will open which causes sodium ions to Rush In And therefore the membrane will depolarize so as you can see over here the milein sheet provides an area of electrical insulation and therefore this causes the action potential to jump along the nodes of runva now you remember thinking why who's jumping what is jumping there's no actual jumping going on if you look at the axon at the top when the first section depolarized as I'm just putting it in a green circle it causes the section adjacent to it or directly next to it to also depolarize so one this depolarizes and then next one depolarizes but for the xon at the bottom however when the first section depolarizes as I'm circling in green it causes the next section which is not directly next to it it's like it looks like it's jumping so first it happened over here and then it happened over there so it implies that the action potential or the depolarization is jumping along the nodes of Runway and therefore this will actually speed up the action potential and by the way we also call this the cator conduction because the celator conduction just implies that the action potential seems to be jumping it's the the the the word jump the word jumping here is used in a figurative sense no one is jumping by the way okay nothing is jumping some students are like teacher is the xon actually jumping no it's not okay right if you still don't know how this speeds up the action potential don't worry let's look at it again I'm going to draw out the axon axon at the top is my unmated xon at the bottom is melinated as you can see over there now let's assume that we stimulate both the axons at the same time okay stimulate both the axons at the same time as you can see here so what happens both sections of the axon depolarizes how does it depolarize because sodium ions rush in fine now this produces a local circuit but look at the local circuit okay the local circuits produced will depolarize the second section right but for the axon at the top it depolarizes directly the next section okay the the section directly next to it but for the xon at the bottom at the same amount of time it jumps and it skips the melinated part and it depolarizes the unmarinated area which is the node of run let's try again what happens then local circuit depolarization again local circuit depolarization local circuit depolarization local circuit depolarization so look at the nerve impulse at the same amount of time that has passed for the unmarinated part they just halfway through the axon but for the melinated axon the action potential has already reached the end at the same amount of time that is how myin sheet actually speeds up the action potential all right right as you can see here I'm just drawing out the arrow the orange color arrows imply that the depolarization takes time to happen it takes one section followed by the other section followed by the other section directly next to it for the unmarinated axon but for the melinated Exxon the depolarization seems to be jumping or leaping along the nodes of run and that is known as the saltatory conduction so if a question were to ask you what exactly is the function of the milein sheet all you have to say is the milein sheet provides an area of electrical insulation which causes the action potentials to jump along the nodes of runva and by jumping along the nodes of runva this will actually speed up the action potential that's basically it