what's up everybody so in this video we're going to be talking about neural signaling there's quite a bit to cover but to be honest it's not that complicated it's pretty straightforward I I think for HL though the the HL only video there will be a lot more detail and it'll be a lot more complicated but for the slhl the core stuff it's not that bad so as usual guys go check out teach me.org for a lot of really really sick um notes and lots of IB style questions okay especially these questions you guys need them to really nail the final exams right get prepared for that so without further Ado guys let's just get started so what the heck nervous system so I've I've already told you so many times in other videos that our body right has so many systems all of which have their own unique different job right for example we got our cardiovascular system which is involved in our heartbeat sending blood all across our body we got our immune system helping us fight infection and disease we got our digestive system helping us break down food and all that our respiratory system to help us breathe so many many systems and here guys we've got another one the nervous system what the heck is the nervous system you may think a nervous like I feel nervous well no it's it's a it's the system that's made up of nerves which are which is a kind of cell okay a kind of cell although your your nervous system obviously is responsible for your emotions and that stuff as well so technically it's it can make you feel nervous but the reason why it's called nervous system is because it's a system made up of these cells called nerves or neurons now um what does your nervous system do so there's a few very key things your nervous system okay as I just said is made up of these little cells called nerves okay and they they have some other names that that you may hear the key one is Neuron this is the this is the name s um we use in science neurons it's the scientific name you may common here a teacher referred to it as nerve cells or nerve fiber but the key one really is neurons so your nervous system is made up of these cells called neurons and these neurons wow look at them man they're looking crazy man they look mad right like they look much different from a standard cell that you think of but they're still a cell they still got a nucleus they still have organel they're just unique and specialized for their job so what is their job these cells these neurons they're special because they can carry little electrical impulses or in other words little electrical signals from one point in your body to another they're essentially your control system they are the messaging system of your body telling what to do what and when to do it and all of these kind of things they control things okay that's what your nervous system is for okay great so we know our nervous system is the control center but give me some examples man what exactly does it do so I'll give you a few things which your nervous system is responsible for okay one big one is muscle control okay yeah you cannot fart without your nervous system okay because your nervous system is going to send these signals to your muscles via these neurons and tell them to contract okay also when you get slapped in the face by some lady after you anoer um you're going to feel something right so sensation your nervous system helps you feel things okay interpret pain or pleasure right sensation that's very very important what else besides muscle movements and sensation there's a many there's like a million more but I'm going to mention this last one here for you guys um emotion memory right without your brain and your nervous system you can't remember things you can't remember who that person is that you keep seeing you can't remember um you can't have emotions you can't be sad or angry okay so there's so many things other than these but these are some key ones I want you guys to be aware of okay your nervous system now as I said your nervous system is just one of your systems in your body but what exactly is it composed of what comprises our nervous system okay we can basically split apart our nervous system into two components the central nervous system and then the peripheral nervous system okay um both of these combined forms your nervous system so what exactly is our central nervous system or your CNS they abbreviated very often as CNS and this one pns okay it's too long to write out the whole thing the whole time so what makes up your CNS two things your brain and your spinal cord okay you can see here and it's kind of makes sense according to the name because these two are most centrally located okay in the midline of your body right and your brain now what I want to say is don't think of the nervous system when you think of the nervous system don't think only of the brain right your brain is merely one component of your nervous system it's merely one component of your central nervous system so it's only a small it's a very big part but it's only one aspect so don't confuse nervous system with brain okay so these are two things making up your central nervous system the brain and attached to it is a spinal cord extending all the way down the midline of your body um protected by your vertebral bones and all that so it's not that easily broken um and it has a purpose and we're going to talk about the purpose just now but for now I want you to know um that this is what's included in the central nervous system now as you can see here the peripheral nervous system this is basically the components that come off of the central nervous system because you have your brain right and your spinal cord as a central nervous system now all of these neurons and nerves coming off of your central nervous system your spinal cord um and going to the rest of your body like your teeniest tiniest toe or your teeny tiniest finger right or your or your your your muscles for for farting all of these places these nerves are considered your part of your peripheral nervous system okay so what do they include two big components your motor neurons and your Sensory neurons so again remember neurons is just the name for the cell that makes up our central nervous system right because all these things your brain matter your spinal cord these guys here they're all made up of neurons little nerve cells um now there are two kinds that comprise our peripheral nervous system two broad categories it's a bit more complicated in reality but for the IB these are the two we need to limit you guys to motor neurons and sensory so motor think of MOT mot as like moving it's doing something it's activating right a motor is something that's um um what do you call it emitting power okay work so a motor neuron is a kind of nerve cell that travels from our C from our central nervous system and then I mean that travels from our spinal cord and will go to our muscles okay to cause them to contract that's why they're called motor neurons sensory would be the opposite sensory means sensation feeling things so these kind of neurons would go from um whatever area of our skin or whatnot and Will Travel towards our spinal cord okay so these are sensory neurons both of these combined we can call peripheral nerves okay these two form our peripheral nerves because these are the nerves part of our peripheral nervous system okay that's the basic sense now what exactly what exactly is the purpose again of the peripheral nervous system then we'll go to the central because it'll make more sense that way so the purpose of our peripheral nervous system as far as you guys need to know is two things one the function of the motor neurons which I just said is to carry information an electrical signal away from our spinal cord our central nervous system towards a specific muscle that needs to contract on the contrary our Sensory neurons will carry information towards our spinal cord towards our central nervous system so that we can feel sensation so what exactly is the function then of our central nervous system three key things one it can receive information if your best friend pinches your arm these Sensory neurons are going to pick up that thing and send the signal towards your spinal cord okay and that's going to be sent towards your brain okay and then your brain your central nervous system is going to be able to interpret that information ow I just been pinched man okay and then your brain is going to think about that and it's going to shate IR response are you going to slap your friend right back what are you going to do and if it decides for you to um punch a friend it's going to send a signal down the spinal cord which will come off in the peripheral nervous system as a motor neuron to go and hit your friend right so that's the that's how they um work together so you can think of the central nervous system as the big boss okay it's going to decide when a message is sent out so you can move your muscles and it's going to decide how to feel about something because this guy your peripheral nervous system is kind of just like a worker for the big boss okay the big boss will decide okay let's move a muscle and it'll send a signal and then the peripheral nerve will go out and move the muscle and on the contrary if you feel pain it will move the signal towards the brain and the Brain will decide how it feels about that and what it wants to do next so the peripheral nervous system is really a worker of the big boss okay and this guy is the big boss he's deciding what's what and he's interpreting everything so that's that's the very key things you guys need to know about the central nervous system and the peripheral nervous system I want to give you guys a silly little example here again to wrap it up and make sure you guys understand the central nervous system um and peripheral nervous system I don't know how many of you guys actually like MMA uh it's just the kind of fighting sport you know um it doesn't matter here's the here's the idea let's say this guy here he's famous his name is John John Jon Jones he decided he wants to punch this guy right they're fighting so he's what his brain or his central nervous system will send this signal down from the brain into the spinal cord down the spinal cord to a level and then it's going to come out and extend this is now the peripheral nervous system right this peripheral nerve will come out and go to whatever muscle he needs to contract to punch this guy now let's say he lands this elbow okay now this guy is going to feel pain there's going to be a nerve that's going to detect that pain and this is the peripheral nervous system right and it's going to go towards the spinal cord and then um send that signal to another nerve which will take it up towards the brain okay now he's going to feel that pain and be like oh what am I going to do next okay he's going to interpret that information and maybe he punches him back maybe he runs away okay that's the idea that's what you need to understand about the central nervous system and the peripheral nervous system okay hope that's clear okay now so we know now what the central nervous system let's go back here we know now what the central nervous system and the peripheral nervous system does um but we actually finally now got to look at the neuron structure we know now neurons make up this nervous system and it's responsible for all this stuff sending all these signals but what is the structure of a nerve cell what's the structure of a neuron so here we got it here's our little neuron remember our neuron right this cell this crazy looking cell is an individual cell that carries little electrical impulses or you can think of it like little electrical signals from one point in the body to another right now wow it's crazy looking right I I got to admit and there's a lot of little structures which you guys absolutely must remember okay cuz on the test they can ask you to draw the basic structure of a neuron or label a neuron so it's very important okay don't don't ignore this stuff it's very very key so let's start off here at this top part here looks crazy like looks like someone who woke up with mad crazy hair right um with one eye now what is this guy here what is this thing here this is the nucleus okay we know every cell has that nucleus right except like a red blood cell but this cell has its nucleus right here and what's this stuff surrounding the nucleus well it's it's got some cytoplasm right and you can even see some little organel right I didn't put a lot of organel here but there's a lot of other organel ongoing here I try to keep it simple there are other organel but I'm only labeling the key things here to the neuron so we got our nucleus we got our cytoplasm and some organel now this whole area Okay the combination of the nucleus and these organel and the cytoplasm we call that the cell body okay the cell body so this whole area is the cell body this is where most of the things are going to happen where they make prot proteins and things like that right the cell body now what are what are these little extensions that come off of the cell body little branches we call them dendrites and you'll see why they're very very very important later but for now you guys should know that basically dendrites are these little extensions that come off the cell body and these areas are going to be receiving little um electrical impulses or little electrical signals from another neuron okay so one neuron will send the signal to this neuron here it will transfer that signal here at the dendrites and then the signal will come in through here and extend all the way down to the end of the neuron okay now before we get to the end of the neuron what's what else is going on here what is this you see this little blue part that's extending pretty much this whole long part okay um don't worry about these yellow things for now but you see the blue like little long pipe we call that an axon axon that is just do whole little pipe through which the signal is going to be sent okay now um you you notice I uh we'll come back to this just now okay so you know you see the axon it runs all the way down and then we get these branches at the end very very similar to these branches here but they're they have a different name okay because this is like the head we call this a cell body and this is like the tail okay but we give this a specific name these branches we call very simple they're at the end of the neuron so we call them terminal branches beginning of the neuron and then the end of the neuron so we call them terminal branches and then if you notice these terminal branches have little blbs little blobs on them at the end we call these terminal buttons okay don't worry about these too much you'll see later um what's what's really going on here at the terminal buttons but for now just remember the name now we skipped that on this area here in the middle remember I said the axon is this blue thing extending through here right now notice these yellow sinks these are actually cells okay these are little cells wrapping around the axon we call these cells okay Schwan cells Schwan cells okay Schwan cells look you got a nucleus there these guys they wrap around the axon and when they wrap around the axon they form many many little layers and we call that the milin sheath and you'll see later wow that these milin sheath they're really really really important okay for now just remember that these cells here that wrap around the axons are called Schwan cells and they um by wrapping around this axon many many times they form a milein sheath I'll show you a picture very very shortly now remember the axon it's this long part and it's being wrapped around by the Schwan cells now these little intermediate Junctions separated by the Schwan cells you see there's little Junction here of axon a little bit of axon there a little bit of axon here these are axon these little pieces of axon we give a name we call the node of ranv node of ran and again don't worry about these these things now this little section here we're going to talk a lot about how this works what's really going going on here for now we're really focusing on the structure I want you guys to just look at the structure look at the parts and get familiar as much as you can now okay let's quickly um run a little bit through here okay run a little bit through here so remember how I said give me a split second remember how I said this axon right this blue little pipe it's wrapped around by the cell so in the very beginning when this Swan cell starts wrapping around the axon it doesn't have many layers as you can see it's like one layer okay but over time it forms many it keeps wrapping keeps wrapping it's like giving it a massive freaking hug okay and it's gives it many layers these layers we call M and sheath okay that's very very important now for now I'm going to mention one split one small sentence on it but we're going to have a part on this later but basically the purpose of these Mile and sheath these Schwan cells wrapping themselves around these axons is to speed up the conduction of this signal when the signal arrives here at the dendrites and it's being sent through to the other side these guys help speed it up it helps send that signal faster fter than the signal would send without these guys okay so that's what you should know for now they speed up trans um transmission of the signal okay sending of this electrical signal but we'll see how it works a bit later okay now two last little bits here how long do you guys think neurons are think about it you know you if we look go back here to this guy if you have your spinal cord and we know these motor neurons to flex your tiniest toe has to come out you can imagine that a single neuron can be really really long think about it a neuron coming out of the spinal cord here has to travel all the way down to your smallest toe so they can be like over a meter long and then you can have other um other other nerves that are really really short like a couple um couple centimeters or millimeters really really short so there's no standard size for a nerve okay so for a neuron okay they can really be they can really kind of go anywhere they can be any kind of range depending what kind of structure you're sending a signal to how far that structure is so there there's a big big range okay and the part that gets longer is this axon so in some neurons the axon will be pretty short and in other ones it'll be really long to extend all the way down to your tiny toe okay so that's very important remember guys as I already said this I'm just going to put this here for you remember the signal generally travels from the dendrites this side when it gets received from another neuron and then gets sent through here here through the axon all the way to the terminal button and then from here it'll be sent to the next neuron okay so that's just understand Direction it doesn't get sent in the reverse way normally gets sent from the dendrites down to the terminal branches the terminal button okay so that's the structure the anatomy of a neuron now I keep mentioning some words like nerve and neuron what the heck's the difference between a nerve and a neuron we know there's many names for neuron like nerve cell um NE neuron or nerve fiber but what's a nerve like what exactly is a nerve what's the difference between a nerve and a neuron basically a neuron is a single cell when you bundle together a lot of these neurons you form a nerve okay many individual neurons grouped or bundled together form a nerve let me show you here a nice little picture so you see here this is a scanning electron microscope so remember an electron microscope can look really really close and this one the scanning one can make it look very 3D it's really really cool I like this kind of image you can see here all of these little circles that's an individual neuron but look they're all grouped together very very nice and tightly and this whole thing is called a nerve okay so you can see the the light blue part that's the axon remember going back to our anatomy the light blue is the most inner side that's our axon and then the yellowy part wrapping around it that's our milein sheath okay so let's label that clearly so we got our I missed I missed it a bit let me fix it for you Lads nerve and then the smaller individual neurons making up this nerve okay that's important hope I hope that makes sense and here's another picture this one is different it's not a scanning electron microscope it's a light microscope so this one you can see obviously they had to add dyes to make the colors appear like this okay guys it's not like naturally like this um so they have some dyes we can see clearly you can see all the little circles what are those little nerve cells but the group of them all together will form a nice big nerve so a pretty good way for you to guys to remember this is you know I don't know if you guys have this but every so often I will bump my elbow on something and I'll have the shooting freaking pain like and we call that we hit our Funny Bone right well we know in reality what did we really hit we didn't really hit a bone we hit a nerve there's a little nerve called your um nner nerve okay and it runs right there by your elbow and it's not really covered that well it's not protected by bone or anything so it's it's pretty obvious so if you accidentally hit that region it'll be a nice sudden unexpected stinging pain okay a shooting pain so what did we hit here a nerve and this nerve is called the nner nerve the nner nerve is made up of many many many many little neurons so that nerve the allner nerve will have many many neurons inside it sending signals down to whatever area it's supposed to supply okay so that's important to understand difference between a nerve and a neuron so guys we've now covered every everything up till here we've covered now the structure the big overview CNS versus pns now we got to figure out how exactly this neuron actually works how does how is this signal sent from one nerve to another how is it transferred through the nerve all of that little good stuff we got to learn this okay and that's like also another very big part of this video but for higher level you guys will learn far more detail so if you guys don't completely understand this concept for standard level it's partly because you guys should not be able to they're not going to we're not going to give you nearly enough information to truly truly get it but I'm going to try and give you um tell you guys what you need to know and try and make it easy to remember okay but really the mouth you guys need to know for IB is very little for for standard level okay so let's get into it so how exactly okay we got our brain here right we're right we we our brain has a lot of these these um these neurons right and they can send signals to other neurons and maybe eventually send signals to your muscles to contract right we know this is going on in our body now how exactly is a nerve impulse or this electrical signal generated how do we make this signal where does it come from let me let me give you a nice little story here if you guys can remember this story the real thing will be so much easier look here we what are we looking at we're zooming into here a bit of the axon right that long little pipe we're looking at the axon so this right here is the inside of our axon and this is the outside of our axon okay now we know it's just a cell so what is this this right here is the membrane of our cell okay the membrane we know it's made up of like a phospholipid bilayer inside this membrane we may actually have like a lot of these little protein pumps and these channels and all that right we know that's going on now look at this little analogy so imagine inside your cell okay inside your house let's say the inside of the axon is like your house inside your house is your family members right the people who belong inside these axons um don't worry later I'm going to tell which what these guys represent but for now just listen to this so inside this axon inside your house is all the people who belong in there right and then outside of your house right is all the people who don't belong in your house they could be criminals and anything like that right now let's say this happens these criminals these people not supposed to be in your house starts going into your house they enter your house what are you going to do as these people start coming in you're going to be in like a flight response you're going to be like oh hell I got to get out of here I don't know if they've got guns or or weapons or anything so you end up leaving okay so initially these criminals when they come in they come in right and you notice people came in so you start leaving you're like hell no I'm going to get out of here and you leave your house okay and now guess what happens now you call the police and everything the police eventually come and and and what they're going to do is what they're going to get these criminals out of your house hopefully hopefully you can catch them and get them out of your house and guess what that's going to allow you to be able to go back in your house right so this little analogy is it's very very important and it's you'll see if you can remember this it'll help you a lot to understand the real the real um mechanism so let's now look at not the analogy version here anymore we're going to look at the real thing okay so here we got our same thing got we got our we're looking at this little axon here we got our inside and outside of our neuron we got these protein pumps and channels and all that let's label some stuff so in this membrane your phospholipid membrane of your neuron right you've got these channels and and pumps let's name them let's name them a little bit so this guy here we're going to call that our sodium Channel this channel only allows sodiums to come through it okay come through it and then this guy here okay it's going to be our potassium one potassium K plus channel so potassium can go through here and then we got this last thing here you guys learned about this in membrane transport it's our sodium potassium pump remember this was a pretty special thing this guy was able to pump sodium and potassium in opposite directions right using ATP okay we're going to look at so it's a kind of active transport both of these are like passive so the the molecules will go down their concentration gradient all right so that's what's in these membranes a sodium Channel a potassium Channel and a sodium pottassium pump now very important part here in a normal cell in normal conditions what happens is we have this sodium potassium pump and so what it does is it pumps what it does is is here this beautiful tip na sodium the cell does not want it so we can say sodium nah na nah and we pump three of and because there's n three things we can put number three here and then K is like okay I want you in the cell and and um you can think of k+ k+ as two k and a plus two and na plus is na plus that's three so this will help you because the sodium pottassium pump what it does is it pumps sodiums out because nah we don't want it specifically it pumps three out so this guy is going to pump three sodiums out of the cell out of the axon and it's going to pump two potassiums into the axon so guess what if this guy keeps doing its job pumping three sodiums out and two potassiums in what are we getting the outside of our axon will have a lot of sodiums and very little potassiums and then the inside of our axon will have have a lot of potassiums and very little sodiums so you can see because of this guy normally in um our um this is the scenario in our axons we've got a lot of sodiums outside of the axon outside of the cell and a lot of potassiums inside the cell okay that's very very important pay attention to this now if we had to measure the charge cuz right we're trying to generate an electrical signal let's measure the charge here cuz remember this guy is pumping three three positive charges out cu sodium is positively charged so it's pumping three out and only two potassiums in so you can imagine after some time the outside will be more positive compared to the inside because we're pumping three sodiums out but only two potassiums in so you can imagine the outside will be more positively charged compared to the inside okay or we can think of it the reverse way the inside will be more negatively charged okay negatively charged compared to the outside because there's more positive outside less positive inside so the inside is more negative compared to the outside so remember we're always comparing it to the outside so the inside is more negative compared to the outside side this is the normal condition okay wait wait one second here going to get some words into your into your guys' brain so you guys need to know a word called membrane potential so membrane potential is the charge difference between across a membrane between the inside and the outside that's called membrane potential the charge difference between the inside and the outside okay now a me we can call something a membrane potential is polarized if one side is more positive compared to the other side then the membrane potential is polarized cuz you know polar means like if someone is bipolar it means they have two they're two they have two Extremes in personality or emotions right so polar just means Extremes in something so if we say the membrane potential is polarized it means that one side either the outside or the inside is more positive compared to the other side okay it's polarized it's not the same it's not the same char charge on both sides that means it's polarized now I know this guys this is a bit much but trust me it's going to make sense here now what is the resting potential so the resting potential is this scenario here it's the charge of the inside compared to the outside when there is no impulse when there is no signal being sent under normal conditions remember under normal conditions this pump is doing its job it's doing this job all the time so under normal conditions this sodium potassium pump is establishing our resting potential it's sending out three sodiums bringing two potassiums in and doing that consistently and that is going to make the inside more negative compared to the outside so that is our resting potential okay so when the neuron is not transmitting an Impulse the neuron is negatively charged inside and this is thanks to our sodium pottassium pump okay so this is our resting potential like I said now here we go now it's going to get a bit more nitty-gritty so this was the hardest part if you understand this now the rest is nice and easy okay look so now remember how I said um the one neuron will receive a signal from another neuron so let's say this part here um this neuron here these dendrites received a signal and we annotate that signal as a positive charge so this positive charge is now arriving here it's arriving it came from another neuron it's now transporting and now it reaches this area here okay this positive charge how are we going to move this positive charge down this whole thing how are we going to move it down here because we want to send it all the way through the axon to the end right so how is this nerve impulse um generated and how is it moved across here look here so what happens essentially is this positive charge is going to stimulate these channels because guess what these channels these sodium channels are very sensitive to charge so as soon as a little as as a little positive charge arrives here cuz remember normally it's very negative in here right I just told you it's very very negative in here so if a positive charge arrives now this positive charge is going to stimulate the sodium Channel which is normally closed because it's negative but as soon as a positive charge arrives now the sodium channel is going to open and when it opens what happens remember there's a lot of sodium on the outside and very little on the inside so if this door opens naturally these sodiums will flow right down down their concentration gradient into the inside and guess what that's going to do that's going to make the inside positive so this positive charge is now going to spread from here where it activated the sodium channel to here okay because now all these sodium channels are coming in all these positive charges are coming in okay when sodium comes in like this um down its concentration gradient we call that depolarizing CU remember um the membrane potential was polarized the inside was very negative compared to the outside side now all these positive charges are coming in to the negative side so in a way we're unpolarized it because we're sending in now positive charges to this side which was negative so we're trying to make it more even we call that depolarizing now when these sodiums are now in here right all of them come streaming in here there's a positive charge right because of all these sodium um because of all these positive sodiums now when it gets very very positive guess what this guy now opens so this guy opens when it when it's a little bit of a positive charge now when all these sodiums comes in it's even more positive so you can imagine right now it's like very very positive in here then these potassiums open these potassium Channel and now guess what there's a lot of potassium on the inside so it's going to very very easily what diffuse out right so remember the sodium here was like our little criminals coming in and now the potassiums is like the people living inside the house leaving right they want to get out of there as quick as they can and so they leave right so now as they leave um guess what happened now now we have the opposite situation that we had when we started now all the potassiums are on the outside and all the sodiums are on the inside that's the opposite scenario that we wanted CU remember all these sodiums are now in here and this positive charge hanging around here now guess what before we move on this positive charge remember all these sodiums come in here and they they fuse and they spread out so this positive charge is now all over the place here here guess what it's going to do now this positive charge can diffuse a little bit all these sodiums as they diffuse and spread out a bit they get close enough to this one here this sodium Channel and now this sodium channel will open because it's sensitive to this positive charge and when it opens guess what now sodiums from here will come in and now this area will become positive and then the sodiums will spread again and cause the next part to happen again so you can see that is how we spread this positive charge all the way from here to the end okay to the end of this neuron okay very very very key now where Did We End we ended here when we said that they're now at the opposite conditions that we started with so now here comes our police car the sodium potassium pump it's going to now sort the situation out remember it's going to take these sodiums specifically what three of them right and it's going to pump them out and then it's going to take two potassiums and it's going to pump them in so if it keeps doing that right what's going to happen eventually then we're going to reestablish our what resting potential we're going to reset our neuron that is now again negative let me just finish this for you guys send some more sodiums out bring some potassiums in so you can see now the sodium pottassium pump has reset our thing to the original where the inside is more negative compared to the outside and now we are ready to receive another let me put this here now we're ready to receive another signal otherwise once the neuron like if this didn't happen then the neuron could receive one signal send it to the end and not be able to function again but now we reset it so it can receive another signal and work again okay now so I just want to put this last one here for you guys so we need to know the last word here action potential so all of these events here the sequence of events that allows an Impulse this electrical signal to travel through a neuron that's called an action potential so basically to summarize it here sodium ions coming in potassium ions going out and the sodium pottassium pump resetting it that's all part of the action potential okay the sequence of events that allows an Impulse a positive charge a signal to travel down okay without these things without this action potential these events happening we could not send this positive charge down the neuron all the way to the end okay that's very very key so remember a nerve impulse is the action potential propagated through the membrane okay so this positive charge moving through the membrane that's the nerve impulse and it can only happen because of the action potential that's allowing it to okay and last thing here remember I forgot to put the word here when the potassiums um go out it's called repolarizing again remember I I did put it here for you guys now remember the sodium potassium pump it's a it's a kind of active transport so this does require ATP guys okay so now we're done all the way up to here right we finished now how an Impulse is generated through this action potential mechanism and how that sends that positive charge that signal throughout the neuron from the dendrites all the way down to the terminal buttons right now we got to figure out the next thing how is this signal moved from the end of this neuron to the next one right because neurons have to work together so the signal will come here it will travel through and now it will like kind of lay it over to the next neuron so that neuron can take that that signal further along the pathway right so we got to figure out that so we're going to talk now about synaptic transmission okay this one's also really interesting I think it's much more easy than the concept I just explained like this whole concept is really really tricky especially um at at SL level because you guys aren't given that much details and information and explanation so a lot of it is really memorizing okay but at least for this next one synaptic transmission it will be a bit easier in my opinion so now now that this signal right we we explained how this signal was moved across with all these this action potential mechanism and eventually now it's moved to the end of the neuron what do we call the end of the neuron again remember from the from the structure one we call the terminal button from here it will be moved to the next neuron so we can see here this is the terminal button but sorry the terminal button of one neuron so I put it here we call this the pre synaptic neuron and and that will make sense very very much now let me show you and this one here is the next neuron so we're zooming in zooming in really really right there okay so what is this going to be this going to be the dendrite okay the dendrite of the post synaptic neuron why does this make sense you see this little space in between the the pre synaptic neuron and the post synaptic neuron guess what this space is in between here based on the names here post synaptic and pre synaptic this must be the synapse right so this area here right in between right in between the two the synaptic terminal B um button and then the dendrite this area here is called the synapse it also has another name called the synaptic cleft synaptic cleft now this area is as I just explained the junction between the two neurons okay or it can be the junction between a a neuron and a muscle because remember neurons activate muscles so this scenario can also um happen between a neuron and a muscle okay but in that case when it's between a neuron um terminal button and a muscle we called we call this Junction it's still a synapse but we give it a more specific name we call it the neuromuscular Junction because neuro means nervous system and muscle me refers to the muscle so it's the junction between the nervous system and your muscle right there okay so now it makes sense why this one here this this this neuron is called our press synaptic neuron because it's before the synapse now this neuron whichever one is trying to relay it to now is going to be called the post synaptic neuron okay now how does it work so when this this signal arrives this impulse arrives to the end here the synaptic terminal end now it's going to do something you notice here how on the terminal buttons there are these calcium channels look here they are also active ated by charge so when a positive charge and in HL you guys learn about and it's going to be called voltage gated channels these are sodium voltage gated channels pottassium volt gated channels and these are calcium voltage gated channels because they're activated by charge now when this charge arrives here it's going to activate these channels to open now guess what there's a lot of sodium a calcium on the outside but very little calcium on the inside so they're going to diuse in now when they come in when they defuse in oh yeah I want to put the steps here so step one here is the impulse arrives I'm going to I have a word summary for this so don't worry so step one here of synaptic transmission is the impulse arrives at the end the synaptic terminal end step two is sodium channels are opened and uh I mean pottassium Cal yeah calcium channels are activated by the charge and they flow in now the third step is these calciums what they do is they have a way of um transporting these vesicles so so these little bubbles here that contain little um molecules in here these are called vesicles and they contain a specific molecule called a neurotransmitter and um I'm going to label it here for you guys but we're going to talk more about what exactly neurotransmitters are okay so they contain these little neurotransmitters now calcium is very is responsible for guiding these vesicles which contain neurotransmitters to the end here the Press synaptic membrane okay right here the membrane here called the presynaptic membrane so it's going to guide them towards there okay now when after it guides them towards there now these vesicles right which contain these neurotransmitters will fuse with the membrane and release the contents through a process called exocytosis right you guys learned about that in membrane transport now now we can now brings us now to the point of what exactly are these neurotransmitters these are little chemicals okay that allows us to send this positive charge to the other side and you'll see exactly how that works cuz at the end of the day we want to somehow move this positive charge through one way or another from here to here okay but how do we do that we need these neurotransmitters okay these chemicals will allow us allow us to send these signals between the two nerves okay but how how does it do it so after after these um let me put the stage there stage four okay so now these neurotransmitters are released and they're going to diffuse right because right here they're in a very high concentration they're all compact now they can diffuse across the synapse towards the other side right spread out this is natural okay now they spread out and go towards the other side now I want to emphasize this um there are very very many many many many different kinds of neurotransmitters many many different kinds in our body um there's only one that you guys have to know about so I'm going to label it here okay and this neurotransmitter is called acetylcholine this is one specific kind of neurotransmitter that IB want you to know about but no we have so so many okay and there is and and they have a very important role in sending this signal to the opposite side if you have problems with your neurotransmitters like the levels are wrong or you're missing one then you can get various diseases such as schizophrenia depression um many many many many kinds of um brain disorders so these neurotransmitters are very important and keeping our our nervous system intact okay so just know you need to know this one kind of neurotransmitter called Ayo choline now this neurotransmitter is released and it's going to basically diffuse across to the other side the post synaptic membrane where it's going to bind to a little receptor so receptor is like a little binding site okay that's all it really is it's a little binding site now once it binds to this binding site uh let me move it around upon binding of acetal cine to the this receptor okay it causes this channel to open okay so that's different remember these channels they were opened by charge remember they're opened by this charge this channel is stimulated by a chemical okay called a NE transmitter so these are chemically gated ion channels when a chemical binds they open so so when it binds now this channel is open now remember outside of the cell what do we have a lot of what potassium or sodium a lot of sodium right we got a lot of this sodium floating around right so now if this channel is open if there's a lot of sodium on the outside and very little on the inside what's going to happen the sodiums are going to go in does this remind you of something something over here when the sodiums diuse in what happens now the inside is very very positive see magic just like that we indirectly sent this positive charge from this side to this side okay okay that's very important so we really depend on these neurotransmitters otherwise we can send a signal between neurons okay we're almost there that was step five by the way binding here and causing sodium to diffuse down its concentration gradient now we're not done though you see these neurotransmitters if we keep them here that's a problem because if they keep activating this neuron guess what you're going to go into a sort of spasm okay because your your neurons are continuously firing non-stop you're not stopping to activate these receptors so these ion channels are always open causing consistent firing and you can get like cramps and and and a lot of mental disorders from this so what happens is there's a little enzyme in this synapse here which is responsible for grabbing these guys so after they release they can bind and after they've bounded and done their action this little enzyme here okay um specific for this neurotransmitter is called acetylcholine estras okay because this enzyme Ace as you know all the ones that end in Ace is an enzyme they will bind this neurotransmitter called acetylcholine and break it down okay now this broken down form can be taken up into the pr synaptic neuron and be recycled and reassembled into a neurotransmitter so that the process can be repeated okay so it's important to know that there are enzymes that can recycle break down these little neurotransmitters into their components and allow them to be reuptake by the pre synaptic neuron and reassembled into um proper neurotransmitters so the process can repeat okay otherwise they'd be consistent iring and would never end and it'd be a problem a serious problem give me one second cool so in a way there's six six steps very key and I'm going to show you now here I hope that makes sense okay so that's how we transmit a signal between two neurons okay so here's the word summary of that I put six steps here as I labeled them so here's all the words you guys need to know so um make sure you know all these things especially the keywords here and it was just by coincidence look here the shape here look looks like a neuron we it happened as we were making this we noticed it just happens to look like a neuron which a neuron cell body which is pretty cool so the next important thing we need to talk about is speed of impulses so we know now the structure of a neuron we know how this signal is formed and how it's transmitted all along a neuron and how it's moved from one neuron to the next now we need to know which things can affect the speed of this process what makes it slow what makes it fast so look here again we got our axon we got the outside on the inside but now we're making it a bit more realistic remember I told you that neurons can have um um can have this milin on it right which was a Swan Swan cell remember let me label it here milin right it was the Schwan cell wrapping itself around the the axon and it had a very important job and I told you it was to speed up this process now how does it do so let me show you so so you know um the membrane right has all of these little channels and stuff like that and by the way while we're at it now remember that this is a 2d diagram in reality it's more like a pipe so you can imagine all of these uh channels and pumps are located in a circle around the pipe so it's not just at the top or at the bottom it's like in a 3D kind of formation okay so hopefully you understand that perspective it's not that important to worry about though now how does this speed up this this process so in this area where milin is there is no channels okay no channels so there's no movement of things in or out at this at these zones here okay so what that means is when the positive charge um um uh gets achieved through the action potential mechanism that we talked about earlier it cannot activate any channels here because there's no channels here so when these um when this positive charge spreads okay it has no choice okay as it spreads but to activate the next area here where there is sodium channels okay so let me put it here for you guys sodium pottassium channels and all that okay it has no choice but to skip this area and activate the next one so you can see these the milin it acts as a sort of insulator to this charge this charge um this charge when it arrives here it goes inside there is no movement in or out it insulates the charge it keeps it inside the axon and forces it to go all the way to this side and activ at the next segment okay and now here the sodiums can come in again the potassiums can come out right the action potential can repeat so remember these little zones in between the the swan cells or these milins are called nodes of ranvier nodes of Ranier remember that the little short bits of axon right in between the milin is called nose of Ranier so you can see here that through this mechanism essentially what's happening is the charge is bouncing okay from one node of r here to the next one it's kind of skipping this area here so nothing is happening in the areas where there's milein so you can see that this saves ATP and time why because if there's no pumps and no thing like that here there's no sodium potassium pump remember the sodium potassium pump uses ATP to reset the resting membrane potential so there's no pumps going on here we're saving ATP but we're also saving time because now the charge can bounce and Skip these areas normally things would have happened things would have had to happen here but now that there's milin we pretty much managed to skip these areas okay and conduct much faster so milin allows us to increase conduction and saves us ATP and time okay this kind of conduction I crossed it out here because I think um I'm 99% sure this is only for higher level so I'm putting the word here in case you guys see it but I'm 100% sure 99% sure this is only a high level thing but this is the name given to this idea of bouncing between NOS of renir is called saltatory conduction okay so that's how we manag to speed up this process using our milin okay that's pretty cool so you need guys need to know this so this was one way in which we can speed up nerve impulses right we can um milin Can conduct Action potentials faster than non-mated axons so when myin is present the signal will be sent faster in areas where in neurons where there's no milin the signals will be sent slower so that's one very important way another one which you guys need to know is the diameter so you see the diameter of the axon the larger the diameter meaning the more space here is the faster the signal is sent okay you guys need to remember these two things there's no need for an explanation there's no you guys don't need to know the mechanism behind it it's very very complex and it's beyond the scope of biology students so just know that both of these things can speed up nerve impulses a greater diameter of the axon and the presence of so we covered everything that you guys need to know about the nervous system there was a lot but I hope it makes as much sense as possible now that is really it though but there is one component one thing that was introduced in this chapter as well which we need to cover because I don't know where else you guys will learn it if your teacher will teach you it in some separate class or something but it's a little thing that we need to learn about case-based questions right it's going to help you to interpret um graphs and things like that and help you put the right answer to get the points okay so let's take a look at it we'll spend a couple minutes on it it will really help you because a lot of people think they understand this and then they go to the test and they mess up and they don't know why okay so let's look at this it's the topic of correlation let me give you an example let's say this my my theory is that the more you study okay the more hours you study per week the higher your GR grades will be so in this example the independent variable the factor being changed was what the amount of hours that you study you can study 1 Hour 2 hours 3 hours nothing whatever right and the thing we're measuring is your score on the test okay so let's take a look here at the graph okay here's a graph it's not very realistic but just bear in mind we got x axis here y AIS so normally the x axxis is the thing where changing so for example the more we go this way that's the more hours we're studying so over here it'd be like zero hours and over here um 1 two so on okay so the x axis is representing the independent variable the thing you're changing now the Y AIS is the is the thing we're measuring so the test scores so you can see here as we go this way the more we're studying okay what's happening the higher the grades are going the more we're studying the higher the grade is if we study this much your grade will here say this much great over here okay so the x axis represents the independent variable and the y axis remembers your dependent variable why am I talking about this so here's the example that I just mentioned because you guys when they show you a curve like this one thing they may ask you is describe the um graph that you are seeing and then you shouldn't say things like oh uh there's a line going up if you say that you're right it is there's a line going up at a slant but you're not going to get the point the IB wants you to use the right words so if you see a graph like this where there is a very very good correlation you can clearly see it's going up like this so the more you study the better your grade will be it's very very clear the data points clearly show it in that case you don't say it's going up you say there is a strong positive correlation because positive means going up so this is the word indicating that it's going up so a positive correlation implies that as you increase um your independent variable so does the dependent variable that's what positive means okay as you increase the independent variable so does the dependent variable so it's going to go up and it's and the word strong implies that these data points are very very um representative of the line it means they're very very close to the line so it's very very reliable okay so this when you see a graph like this you should say it's a strong positive correlation okay now let's look at another one how does this one look looks very similar to this we know it's positive it's going up right but it's weak because the data points are not that consistent to the line they're not sticking that close to the line it's more like I can kind of see there's a line but it's not that strong so in that case you say it's a weak positive correlation okay very important words to use these will get you to points so you can see a good example is hours of sleep and height so they're saying here the more hours you sleep the taller you'll be this is you can see the graph shows a weak positive correlation and that makes makes sense because um hours of sleep is not the only thing determining your height there are other things like your diet or your genetics right so therefore there's a weak relationship okay it's not a very strong relationship let's look at one more can you see any Trend no it's a so this is called no correlation so don't say nothing say no correlation and an example would be shoe size and intelligence okay because people with big feet can be stupid or smart people with small feet can be stupid or smart Okay so there's no correlation for this one that's very very key so um now the key thing here I need to um address here it is very subjective so if I give you a graph that looks somewhere in between this one and that one what will you say will you say strong positive or weak positive you won't know right because that's very subjective it's up to the person therefore they invented this way to quantify it so they made a thing where they call it R they denote it by r so the correlation coefficient or R will denote the strength so they'll basically give you the strength in terms of a number instead of just looking at it and guessing Okay so the number is between zero and one the closer the number is to one the um that means the stronger the correlation is so this one here would be zero and this one would be close to one not perfect but very close to one okay that's very very important to know now if you square this R so whatever value you get for R and you you square it that will give you the variance it will tell you how far how closely packed these dots are to the line to the line of best fit so you can see this one's variance or R squar will be very very close to one meaning they're very very close to the line this one's r squared will be very very low because the dots are very far from the line okay so those are two key key things you need to know r and r squared okay let's look at one more thing so use these words when you do the case based questions don't say it's there's a slant you're not you're right but you're going to you're not going to get the point so let's look here at the next one so this what's this one it's going down so now we say negative correlation so this is a strong negative correlation okay it's not sloping down it's a negative correlation because as you increase the independent variable the dependent variable decreases so it's a downward sloping next one this one is the same thing but weak okay because the dots are not so close to the line of best fit and again here no correlation the difference here is when we look at r instead of being 0 to 1 now it's 0 to 1 okay so when someone tells you the R value is negative 1 or anything negative then you know it's sloping down if the R value is anything positive then you know it's sloping up okay so it's either between zero and one if it's positive or Z and negative 1 if it's negative okay so that's what you guys need to know so that's it for this idea make sure you use these words they can be really helpful to not losing stupid points so now let's do some three questions okay where do Sensory neurons send signals to and from try it yourself guys and the answer is a it sends it from your central nervous system I mean to your central nervous system from the sensories receptors the areas that pick up the pain okay in your peripheral nervous system now which neuron structure receives an electrical impulse from another neuron right one neuron will send the electral signal um from its um terminal bulb to the dendrit so it's going to send to this one's um cell body and this one will send it down here and then from here it will be sent to the next one stend writes so it's going to be a last one here by means of which mode of Transport are neurotransmitters released from the pre synaptic neuron into the synaptic Clift you remember the vesicles they fuse with the membrane and release it by exocytosis then those neurotransmitters diffuse across to the other side to the postoptic membrane okay so I really hope that was useful guys there's a lot and I really help hope it helped you in some sort of way and I will see you guys in the next one