[Music] in this video we'll be looking at nerves and we'll be looking at their structure their functions and just everything about them and to be honest this is probably one of my favorite topics as well just because it is so interesting to see how everything comes together so in the human body we've got around seven trillion nerve cells also known as neurons now there is a wide range in length of these neurons but the longest one that we have just what interests sake is the sciatic nerve and on this diagram on the right hand side the sciatic nerve starts in your lower back and it travels all the way down your leg and it ends in the heel of your foot now one of the common things is sciatic nerve pain or if you have got pain it starts to resonate from your buttocks and it goes down all the way down your leg and that sometimes if the nerve gets pinched by something weird a movement that you've done during exercise so nerves use electrochemical messages to communicate so electro meaning electrical so the impulses that are generated and then chemical has to do with the synapses where they use neurotransmitters some chemical compounds but we'll look at that a bit later on now I've added this picture here on the side and this is actually from the body Wolves exhibition now it is a bit graphic so I've put a description in the description tab I've put a link to their website and you can just go google some images as well of the Body Worlds exhibition it is graphic because it is real people that have donated their bodies and then they get they go through the whole process of plastination and then they bought their bodies are posed in different positions but this one actually is quite interesting because it shows the nervous system of the human body so you can just see how delicate and how vast the structure is in the human body so if you want to go have a look at that that's also something nice to see but I do warn you guys of the graphic gun thing because I know some of you are quite sensitive to stuff like that another cool thing that you can go check out is the movie 127 hours I don't know if you guys have seen that it's with James Franco well it's actually just one portion of the of the movie that is quite interesting it's also once again very graphic so if you go look for the specific clip on YouTube you can just search something like 127 hours on cut but it is like I said very graphic he actually has to cut off his arms so he's a he's a hiker that he went out so nobody knows where he is he didn't tell anybody where he was going and then he ends up in this like crevasse area and the ball that actually falls on his hand and the only way he can get out is by amputating his own arm and that he does using a very blunt pocketknife so you can just already imagine imagine what's happening there but in the one portion of this clip he actually has to cut through a nerve and you can just feel every bit of a pain that he is going through so if you want to have a look at that and you've got the stomach for it go ahead now looking at the functions of sensory and motor neurons so firstly let's look at the definition so a sensory neuron conduct impulses from receptors to the central nervous system so the receptors are now different parts of your body that will be receiving that stimulus so for example on your hand you will have a receptor that picks up that stimulus and converts it into an impulse that will be then sent to the central nervous system and then with the motor neuron it conducts impulses away from the central nervous system to the effectors now just looking at the definition of an effector I think it's on this side okay here it is so an effector is an organ or cell that acts in response to a stimulus so that will now be for example the muscle of the arm reacting to that stimulus so let's just quickly when something is conducted conduct impulses from the receptors to the central nervous system using this picture on the right hand side so let's say somebody touches a hot stove plate that impulse then gets sent through your sensory neurons to your central nervous system where that information is then processed now so it's taking it to the central nervous system with the motor neuron that conduct impulses away from the central nervous system and takes it back to the effector organ so a way and two very important you know the difference between the two now with sensory neurons and motor neurons they do have two other names I don't it doesn't matter which one you use I'll know the difference between the two obviously I just think it's better for you to use sensory and motor because those two names are very similar to each other so sensory neuron is also known as an efferent neuron and I remember that by looking at the a and connecting it with the word arrived because the sensory neuron transmits impulses to the brain so it's arriving at the brain where with a motor neuron it is known as an efferent neuron and efferent I connect the e with the word exit so it leaves the brain and goes to the effectors so those are the two other names that you can use now looking at the structure of these two neurons you only need to know about dendrites the cytoplasm the new is the cell body the axon and the myelin sheath now this specific diagram is from the Anza series book it's in part one the nervous system is in port one or responding to the environment and this one is on page one point 28 if you want to have a look so according to your exam guidelines you only need to know the ones in red and their functions as well so you can already see that a motor neuron and a sensory neuron have quite a different structure about them the motor neuron is also known as a multipolar neuron and the sensory neuron is known as a unipolar neuron now what does that mean looking at this diagram you can see that the motor neuron at the top has quite a few of these branches coming out of it and those branches are called dendrites so having multiple of those outgrowths or a large amount of these dendrites is what classifies it as a multipolar neuron looking at the sensory neuron also known as a unipolar neuron it only has one outgrowth and that is the cell body over here so that's their only outgrowth it has it doesn't have multiple outgrowths like this cell body of the motor neuron okay so let's quickly look at how impulses get transferred through this so an impulse will enter the the neuron through the dendrites that's the entry point it will then go through the cell body information gets processed and then that impulse is synced down this way through a structure known as the axon so the axon then transports that information and then it will accept this neuron through something called a terminal branch of the axon so that is the end of this neuron and then you'll have another neuron multiple neurons sitting at the end of this terminal branch and then that impulse will jump to this one through an area called the synaptic gap or over it and we'll look at that now and then it gets sent down the same process and so it carries on now these neurons don't touch each other they there is a gap that's why I'm talking about a synaptic gap but before we get there let's just look at some of the other structures now also with a sensory neuron same thing impulse enters through the dendrites travels through the axon through the cell body and then in exits through the terminal branches of the axon so the cell body is this massive area here and that area of the day and in the cell body you'll find the cytoplasm and the nucleus we've already discussed the dendrites and axon then the myelin sheath is the structure around the axon we'll look at the function now so let's quickly and then there's another neuron it's called an inter neuron and we'll look specifically at this one when we look at it something called a reflex arc you don't need to know this specific neuron as well as the motor or the sensory neuron but you didn't do you need to know the purpose of it when we get to the reflex arc looking at the structures and in the functions of these parts the cell body that consists of the cytoplasm with a nucleus the nucleus what does it do it controls all the cell's functions then the myelin sheath which is that area at the top here it surrounds and insulates the axon of a neuron in order to accelerate the transmission of an impulse so it just makes that impulse move faster through the axon then the axon which is this long structure this branch going down from the cell body in them in the motor neuron and same on this side so what does the axon do it conduct smooth impulses away from the cell body and then the dendrites which are these branch like structures at the top they are there to conduct nerve impulses to the cell body next we'll look at the reflex arc so here you need to know the definition of a reflex action and then a reflex arc then you need to know the different structures and in their functions of each part I mean explaining that by looking at a diagram and using these words so this isn't your exam guideline so if you I just want to go over look at that a bit later on that would be good you also need to know the functioning of a simple reflex action using an example the significance of a reflex action and then the significance of synapse --is looking at the definition of a reflex arc and a reflex action so reflex arc is a pathway along which an impulse travels from a receptor to an effector to bring about a reflex action so it's it's basically the reflex op is just the pathway that is followed then the reflex action is a rapid automatic response to a stimulus this is to minimize any harmful conditions to the body an example is when you have a hot stove or you prick your finger on a needle and then the body's response in removing that body part to minimize the harmful effects on the body that also brings us to the significance of a reflex action so it protects the body from further injury because you've already touched the hot stove and you've already pricked your finger so there's already injury but it prevents further injury from you burning your hand further or damaging your finger further so it is a quick reaction from the spinal cord and not the brain and this is not to overload the brain so this reaction is from the spinal cord so let's look at this practically this reflex arc so the definition for arc is moving with a curving trajectory okay so basically once we do this reflex arc route now you will see the curvature that happens so when you describe the reflex arc you need to be using certain words like they mentioned in the exam guideline so we're going to be talking about a stimulus we're going to be talking about an impulse the different neurons we're going to be talking about the spinal cord where it enters the spinal cord the synaptic gap and then the motor neuron where it exits and then when it goes to the effectors so we'll look at that in detail when we study this diagram now so they've asked this in quite a few exams generally something with an open flame or these even a needle involved and then they also sometimes ask this a new example so how do you interpret this so firstly there will be a receptor in this case it's the finger that receives a stimulus now this stimulus is the heat from the flame that stimulus is then converted into an impulse now that impulse will then travel through the sensory neuron towards your spinal cord so that impulse thing Travis travels through your sensory neuron towards your spinal cord when it gets to the spinal cord there are two entry ways or entry and exit so the first one is the so root of the spinal cord so that is where the sensory neuron enters and then it will exit through the ventral root so dorsal means top and ventral means bottom so this stimulus now travels through your sensory neurons as an impulse towards the spinal cord that impulse then enters your spinal cord through the dorsal root and then there is going to be a transfer of this impulse between different neurons so now we are currently with the sensory neuron but now it is going to go through this neuron here which is a inter neuron it is known as the inter neuron and going back to this diagram at the bottom it's this one over here so an inter neuron just serves as basically a bridge between the motor and the sensor neuron century in Iran so that there can be a transfer of impulses so it pauses the synaptic gap so between the neuron so let's say this is the terminal branch of the sensory neuron then there is going to be a gap between the sensory neuron and let's say the interneurons dendrite so they're not touching each other but that impulse has to pass through that gap in order to get to the next neuron which is the inter neuron so it causes the synaptic gap it enters the inter neuron then it's going to exit the inter neuron bypassing the next synaptic gap so let's say the inter neuron also has the terminal branches and then the motor neuron is the next neuron that it's going to enter through not my best drawing so now it has to pause that's a synaptic get there as well as soon as it passes it it enters the motor neuron so it's now in this area now the motor neuron is going to exit the spinal cord through the ventral root of the spinal cord so this bottom exit and then it's going to travel that impulse is going to travel down the motor neuron and towards the effector and what it's going to tell the effector organ in this case which is a muscle it's going to tell it to contract and withdraw the part being stimulated so then you're going to have that upwards jerk of the end now remember this happens within split seconds all these impulses being while traveling up and down and that is for you this is an involuntary reaction so you're not thinking about it your body just does it on its own so what do you need to know yeah you need to know the route that is followed by the reflex oh and I hope you can see the arc now so let me find a different color so this section yeah is the reflex arc that information is coming in I mean it's making almost like a u-turn and coming back so moving with a curving trajectory and it's going back to the effector like I said they like asking this knee example as well sometimes they'll even ask you what happens if the sensory neuron is not allowing the impulse to travel through or even the motor neuron but we'll look at that when we do some examples of all the exam questions so once again there is a stimulus that stimulus is the hammer of the doctor hitting a certain spot on the knee to take your reflex actions that stimulus is then converted into an impulse that travels through your sensory neuron and enters your spinal cord through the dorsal root it then passes the synaptic gap and enters the inter neuron and that impulse travels through the inter neuron passes another synaptic gap and then goes into the motor neuron because now we've got a message of what has to happen there's an nothing impulsive will tell your foot what you do travels through the motor neuron exits the spinal cord through the ventral root travels down and to the effector muscles in this case which is your your quads and your hamstrings and then that impulse tells your foot to move your leg in that matter for that matter to move up or down so now the synapse and its significance it is a small gap between neurons known as the synaptic gap these neurons these three types of neurons sensory neuron inter neuron and motor neuron they don't come into contact with each other they don't touch each other looking at this in a more zoomed in version so looking at that area over there we've got the terminal branch of one neuron coming close to the dendrite of the neck so this is the terminal branch and then this is the dendrite of the next one that little area over there is known as the synaptic cleft or the synaptic gap and it's through that gap that the impulse has to travel in order to get to the next neuron so what is the significance of a synapse so it allows impulses to travel between neurons so for that impulse to go from the sensory neuron into the inter neuron and from there into the motor neuron and then it it allows the impulses to pass from the terminal branch of one year on to the dendrite of the next we've talked about that already and then it allows impulses to travel in only one direction we only want an impulse to go in one specific direction because if it goes back there's going to be a major glitch and your body's gotta start malfunctioning it also allows multiple nerves to join and split so at this terminal branch of this motor neuron you could have the dendrites of a next motor neuron coming in and even one over there and another over yeah and then it also ensures that they aren't an overload of stimuli that is felt so when we look at that if you can get dressed in the morning for example you are going to feel your clothes being put on but after that you don't really pay much more attention to the feeling of your clothes on your body and that is because of the synaptic gap or the synapses that basically cut out that stimuli stimulus in order for your body not to overload your brain with too many messages coming in or out so that is what helps you and until you start thinking about your clothes on your body then you will start receiving that sensation again but otherwise that is cut out completely now looking at how this impulse will travel from the one neuron to the next that is done with some chemicals known as neurotransmitters and this is dopamine for example is one and then serotonin is the other so these chemicals they they are others but these are some of the better known ones so these chemicals take that impulse and they carry it over that gap to the next dendrite now as soon as they reach the other side they are enzymes that are ready and waiting as soon as those neurotransmitters reach the side those enzymes basically break down those neurotransmitters so that they are not able to carry the impulse back and this is what happens with people that have Parkinson's for example they don't produce those enzymes anymore so those neurotransmitters don't get destroyed which means that impulse is going back and forth the whole time which causes those people to have quite a lot of jitters I think that is all that I wanted to say with regards to that and I actually have a micrograph here to micrographs of neurons so it's a picture taken through a microscope of a neuron so this is the cell body the nucleus and you can see there's multiple cell bodies next to each other so allowing that's what the synapse is a foo so it allows multiple nerves to join or split as you can see in this picture of the year now just for interest sake your brain has 86 billion neurons in it now that is quite a large amount and researchers have previously thought that it was close to a hundred billion but the most recent information that we have is that it is close to 86 billion and it's quite interesting how they got to that conclusion and I've placed an article a link of that article in the description tab so if you guys want to have a look at that just for some extra reading that would be nice and that is the end of this video [Music] you