hi everyone and welcome back to Advanced hology today we're continuing with unit one cells and proteins the fourth CA communication signaling and we are nearly finished it we're on to Part D nerve impulse transmission now like I mentioned in my previous video I'm annoyingly going to split this up into two parts this is part one generation of a nerve impulse we look at essentially what a nerve impulse is and how it is created and then part two will be a bit shorter and we look at more of a sort of case study of how this works in the eye um the reason for this is is quite lengthy it's quite complicated so it just breaks up uh even more than we normally do with these keyas so let's get started first of all with nerves hopefully you remember from National 5 biology about your sensory enter and motor neurons and that we have electrical messages being transmitted along neon and then those messages have to cross the scaps through chemical Messengers neurotransmitters uh and that's really the most that we talked about um if you did hire hire human biology sorry you will know a bit more detail about this um it's not required for this so don't worry if you if you didn't H but what we're really going to be looking at is more applying our knowledge of advanced S biology particularly in terms of membranes and how these electrical messages are actually generated so uh first of all we're going to go through a few terms that we're going to discuss in this area cuz like I said it it's quite lengthy it's not really the most exciting to be perfectly honest um but we need to S of learn some terms then we look at step by step how this electrical message is generated and then we'll move on to the ey in the second video so first of all these nerve impulses these are signals that are just transmitted along a nerve fiber these electrical messages um however if you have a look here it's important to remember that we have these membranes along this nerve and these different membrane proteins of which there's going to be a constant Flux Of I going back and forth so again looking at this through M lens or Advance higher detail it's not just electrical signal how is that electrical signal actually generated so first of all you might remember the term resting membrane potential now if you remember this is a state where there is no net flow of ions across the membrane so there's no net flow this is just the resting uh potential and any change in the flow of ions is then going to have an impact on that potential so if we were to actually generate an earth impulse we're going to need a change in that membrane potential so therefore we're going to need ions moving in ions moving out going to have some form of effect here this diagram at the bottom we will be coming to in a lot more detail so don't worry if you're looking at this what's going on here um essentially this is looking at the changes in ion movement and what the effect is on what we call the action potential now an potential itself is just a wave of electrical excitation along that me membrane so again the ions are going to move that's going to lead to a change in the membrane potential that's going to lead to this wave of electrical expectation colon action potential that's going to cause this signal if you almost think about it like uh looking at a heart rate monitor and the sort of beeps going up these Peaks and lows there that's essentially what this looks like this generation of electricity um now we're going to come across two words depolarization and repolarization it's important to know the difference between between them and be able to spot them in these diagrams and such so first of all if you look at this diagram here you can see uh what's label is part two we have this part called depolarization where the voltage is increasing and we're hitting this action potential now depolarization is a sudden change in that membrane potential usually it's going from a negative or a relatively slightly negative charge to a positive charge uh you can see again on this graph down here that it it is negative but not massively so and it's going to increase from negative to positive have that Peak and that would be depolarization um when that happens that's going to be caused by the entry of positive ions if you add in positive ions there's then going to be opening of these voltage gated sodium channels so essentially we're looking back at our sodium potassium pump and if that triggers the opening of more of these channels then there's going to be more depolarization and the more depolarization takes place place the higher this action potential is going to get to ultimately though we will get to a point where these sodium CHS are going to close they're going to be inactivated what then happens is that leads again to the opening of these pottassium channels like we've talked about before and we're going for a period of repolarization again in this diagram here you can see this acal drops down and we essentially head back to that resting membrane potential so depolarization going up repolarization charge going down just so you're aware of those cuz sometimes people get quite confused um now with the synapses this part here is going to go through the the process briefly and then we going sort of repeat it but sort of Chunk it up a bit nicer but just so you know how this all essentially works as I said you mentioned synapses in naal 5 biology all you really talk about was syapse are the gaps between neurons and neurotransmitters a little chemicals that move the messages between the synapses now essentially that's all we need to remember for this part here these neurotransmitters again they don't just sort of carry a magic message across the Gap what they're actually doing is they're moving across syapse they're uh binding at the end of a sinapse and they trigger the opening of these Li gated ion channels uh those ion channels Ang go cause movement which is going to lead to peaks of these depolarization and this this action potential moving throughout uh the whole of this nerve so essentially this neurotransmitter is going to bind it's going to open up these iron channels that are liing gated if there's then going be depolarization but if there's enough depolarization if there's a sufficient amount of iron movement um and we go past what we call a threshold value then there's going to be the opening of voltage gated ION channel sorry sodium channels and there's going be more sodium ions entering the cell okay um like I said we'll go through this in the graph uh think of threshold value almost as like the action potential um or sorry the activation energy of an enzyme reaction you need to hit that Fresh Value to go beyond that in order for more depolarization to take place if there's depolarization but it doesn't hit that threshold value then it doesn't trigger the opening of the rest of these voltage gated sodium channels so we have that change in membrane potential and then as we said we have this depolarization the charge goes up but eventually after a short time the sodium channels are going to come inactivated and then these voltage G potass channels then open pottassium ions move out of the cell and we have this charge decreasing through repolarization and we restore resting membrane potential now like I said we're going to go for this just in a little bit more detail here I think it's quite helpful to visualize it on the graph um and also just so you know each part here but that is essentially the whole U the whole process that's really all you need to be doing about this so again just to look at this on the graph if we have step one here we have the stimulus we have the ions moving and we need this um this depolarization to hit the threshold before we have Fuller depolarization and the movement of all these sodium channels so you can see on the yellow lines down here there's failed initiations so that's essentially where there's been some I movement but not enough to hit the threshold value uh then what happens is we have this action potential being generated if look at step two so this F depolarization going on this is this rapid change in membrane potential as said the sodium channels are now open there's now loads of sodium ions going in and we have this big increase in the positive charge of this action potential in setep three mentioned before we then have repolarization because these sodium ions are now inactivated they're closed and now there's going to be this e-lux or exit of pottassium ions leaving the cell uh from the activated pottassium channels that are now open and as you can see the charge now decreases and we go down um to our resting stage now there is a period here at the bottom called hyperpolarization uh this is basically where the mem potential is lowered because there's been such a change such an exit of those potassium ions and the pottassium ion channels are now closed but we get back to this resting state where the membran potential returns to that that resting voltage that resting membrane potential okay so we can see in all these parts here we're then back at five and then if there's more ion movement then sodium channels are going to open up if they go past the threshold value more depolarization shutting of iron channels opening of potassium channels D repolarization and this process just repeats itself now another part to look at here and this diagram tries to show this kind of movement along a uron but deoration of a patch of membrane then causes these neighboring regions of a membrane to also depolarize and they go through the same cycle so again when we go back to this diagram here I mentioned earlier thinking about a heart rate monitor and these these bleeps these um these Peaks going up That's essential what's happening is once we have this action potential here and we get to the resing state the neighboring PCH of that membrane is then going to go through the same process as well and that's just going to move for example here from left to right all the way through this nerve obviously once we get to the end of inur know we hit that syapse that we mentioned beforehand so when that actually potential finally reaches the end of the nerve it's going to cause these visal which contain neurotransmitters so remember these visal these little um these objects are able to carry uh these messages across they're going to carry neurotransmitters um to the membrane then going to send them across to be released and stimulated response in the next cell so and again once we have that you're going to have more depolarization taking place we have the restoration of that resting membrane potential you're going to have the inactive voltage gated sodium channels to go back to its normal confirmation which then mean they can open up again if there's more depolarization to release more of those sodium ions which then is going to lead to an inactivation uh depolarization the repolarization and opens up the pottassium channels so again this just goes on and on essentially and just a reminder there as well repolarization is that these ion concentration gradients they are reestablished by the sodium potassium so like I said before this whole process is being generated by sodium potassium moving in and out of these membranes uh and this this active transport of these is what's generating this electrical impulse the whole time around okay once we have that again you get back to your resting potential levels so again if you just remember your resting uh memory potential is just your your normal stage there is no net movement of any of these uh ions but again if there is then going to be a change that's going to to your depolarization and eventual repolarization so like I said that's quite a complicated part hopefully it's explained a bit more of a way that will help you out but that is the last part of um Kia 4D part one uh like I said we will go on to a second video shortly where we're going to look at nerve impulses in responses to a stimulus in the eye so therefore light signaling uh and that'll be the last part of ker 4 which means you only have ker 5 left of unit one okay so make sure you've watched part one first and you're comfortable with the terms depolarization repolarization like I said I think that graph is quite useful to go through and just make sure you know all the stages um quite a useful one to know for say a four mark question be able to label out the exact processes what's happening what's a threshhold value what channels are opening for depolarization or repolarization and what's remembering potential so again thanks so much for listening folks uh appreciate all the comments uh coming across I know people are um concerned about how quickly videos are coming out we are getting back into them and hopefully there'll be enough for you uh to be revising for say upcoming assessments prelims that sort of thing so again thanks so much for listening folks and I will speak to you next for n policies in response to Environmental stti