for this particular part of the video what we're going to be looking at is we are going to be comparing the structure of the sensory neuron and motor neuron in the previous video I told you that you must be able to recognize how the sensory neuron relay neuron and Moto neuron look like all right you must know their function as well by the way and you must also know that the central nervous system uh is consisting of the brain and final cord which I've highlighted in that very U mild green color all right and the relay neuron I've also mentioned it in the previous video that they are located fully inside the central nervous system video is not technically about the relay neuron what we do have to also understand is some parts of the sensory neuron is also located it they are partially within the central nervous system and the Moto neuron is also partially within the central nervous system system as I'm circling in red you can see portions of these two neurons that are embedded within the CNS the brain or the spinal cord but I'm going to remove the relay neuron because we don't really have to focus on it what we do have to know is we have to focus on the structure of the sensory neuron and Moto neurons that is important for the exam now the first thing we want to do is look at the parts where I'm highlighting in yellow those parts where I'm highlighting in yellow for the sensory and Moto neurons they are referred to as the cell body the cell bodies are just these particular parts of the cell where the nucleus is found okay so you can see the nucleus within the cell as well the weird thing over here that you must know within the difference between sensory neuron and motor neuron is as follows the cell body of the sensory neuron are not within the CNS you know it's not within that green color border of the brain and spinal cord but for the motor neuron however the cell body is within the central nervous system you must know the difference between the two of them okay that's the first difference that we notice okay they have some similarities but they have differences too the second part is the elongated structure which I'm highlighting in blue that is referred to as something called axons exons are just these long structures and by the way even though these are individual cells some exons can go up to a meter long yes one single a single newon can sometimes be up to a meter long long because the reason why axons have to be long is because they have to transmit impulses over long distance then so those are similarities between the sensory and motor neuron they both have axons another similarity is they also have these parts where I'm highlighting in Orange you can see that those are referred to as dentrites they look like Roots don't they and the function of the dentrites are to just increase the surface area when receiving signals that's all we just have to know about it so the more brunching you can see in the dendr just like the roots of the plants it increases the surface area not to absorb watered minerals by the way these are not Roots even though they look like Roots they are to increase the surface area so they can easily get signals or electrical impulses from other structures as easily as possible okay and then we also have the parts where I'm highlighting in our gray those are referred to as terminal branches or the end branches and the terminal branches have this kind of like ball or grape like structures and those grap like structures are referred to as the synaptic knob okay and the synaptic knob will contain vesicles with neurotransmitters okay we will talk about the synaptic knob in a much later video what we just doing over here is we just comparing the structure of the sensory and motor neuron in which both have cell bodies both have axons both have dentrites and both also have terminal branches and synaptic knob the only difference over here is the structure of the cell bodies uh for the Moto neuron the cell body is located at the beginning part of the neuron but the cell body of the sensory neuron is located in the middle somewhat in the middle and then uh you can also say that for the motor neuron the cell body is within the central nervous system but for the sensory neuron it is not so these are some of the similarities we must know and the differences as well now another thing that I also want you to understand here is as follows I'm drawing out the sensory neuron and motor neuron as you can can see that you can see the axon but on the right side the axon has this kind of weird um I don't know how to describe it like cake not cake uh sponge kind of like orange color sponges uh intermittently found along the axon that weird that weird Peach highlights that I've put over that so what exactly are those now those are referred to as something called as the milein sheet now some students will ask the question do all on need to have the mine sheet not necessarily some neurons do not have mine they do not have the mine sheet so we refer to them as unmyelinated axon but if the neuron has something called a mine sheath or myeline layer we will refer to it as something called the melinated axon now upon closer inspection of the uh Exxon over here we notice that and oh by the way what neuron is this you must be able to rec this this is a motor neuron right here how do we know that's a motor neuron because we can see the cell body it's forming that kind of head at the end of it right now um this motor neuron has mine sheath and upon closer inspection of the milein sheet we notice that the Ming sheet does not cover the entirety of the axon they are kind of like uh a little bit Gap a little bit and then a Gap a little bit and then a gap so wherever that you have the orange color or peach color layer that's known as the milein layer or the milein sheet but the parts of the axon that do not have the milein sheet are referred to as something called the nodes of ranvier so R if I'm not mistaken I think the person the person who discovered this was called R I might be wrong here but yeah we're not going to go through that in detail but um the point of the matter is parts of the axon that are not melinated are referred to as the nodes of run is this important yes am I going to talk about it now no okay because we will talk about it later but one important question I love asking my students is as follows is the milein sheet actually going through the axon is it piercing through the axon how does it actually look like right so upon closer inspection this is just the longitudinal view of the milein sheet you can see the milein sheet it kind of looks like it's going through the axon isn't it but when you look look at a diagonal view or the three-dimensional version over here purple color is the axon is the myin actually going through the axon no it's not the myin is actually like a cinnamon roll I'm a bit hungry okay don't mind me um the myin she is actually twirling around the axon it's spiraling around the axon the axon is kind of like a tube right and the milin is actually going around it okay swirling around it instead of going through it okay it's not pierc ing through the xon at top and if we were to look at the crosssection I'm coloring the xon in purple so you can see it more clearly if we were to look at the cross section you can see the axon and the myin is actually like a kind of a snake if you will and the snake is just going around and enveloping the accent that is referred to as the Ming sheath and here's the interesting thing the milein sheath is actually a separate type of cell it's a particular type of cell that is wrapping around the axon to form the milein sheet and the name of that cell is called the Schwan cell okay so now students will then get very confused they they'll be like okay let's say they they have an arrow pointing towards the milein sheet do I call it the schanel or do I call it the mine sheet in the exam you can call it both if you wanted to normally in the exam if they just point towards the layer as that arrow is doing right now and if they ask you to name that thing you can just name it as the milin sheet or the schan cell but if they were to specifically ask you a question what is the name of the cell that makes up the mine sheath then you have to say it's the Schwan cell that's basically what we have to know for this all right and of course what are the parts think remember again the parts of the Exxon not all parts of the Exxon have the milein sheet by the way the parts of the Exxon that do not have the mine those small little portions they are known as the nodes of runva okay I'm just labeling the nodes of runva for your reference over here as well all right now what is the function of the milein sheet some of you might know that the function of the milein sheet is to speed up the transmission of the impulse I'm not going to talk about it now because we first have to talk about electrical impulse in detail then we will come back to the milein sheet this particular video is just looking at the structures okay so this is just the introduction to what the Ming sheet on the axon is all about