so in this particular video we are going to be looking at the structure of the nervous system and as I've mentioned in the previous video this nervous system is this particular organ system in our body that transmits something known as electrical impulse from one part of the body to another part of the body and they do it extremely quickly so your nervous system is divided into well the central nervous system which is made up of your brain connected directly to the spinal cord now a lot of times people might think that the spinal cord is actually our backbone no it's not the brain and the spinal cord are structures that are encased or protected by the bone for example your brain is protected by your skull and the spinal cord is technically a very soft organ that is protected by your backbone so you cannot directly touch your brain or spinal cord okay because they they're protected by bones so that's a good thing you know because you don't want it to be directly exposed to pressure number two we also have something called the peripheral nervous system and the peripheral nervous system are made out of uh cranial nerves which are just nerves or you can think of it as like wires which are connected to the brain which I represented in green as you can see there looks like an alien by the way and the spinal nerves which are connected to your spinal cord okay and these nerves uh basically help together with the central nervous system the cranial n nerves and spinal nerves are supposed to transmit electrical impulse and I will explain what electrical impulse or Nerf impulse is in the next video okay now what exactly are nerves though uh I like to ask my students this question sometimes are you able if we cut a person open are we actually able to see nerves sometimes you can actually see nerves because nerves are tissues so they are made out of many cells grouped together and you can actually see fine nerves running along the person's body but they're quite deep and usually we can see them during surgeries so in this case over here the nerve is a tissue and they're made out of cells and the name of the cells are called neurons and if you remember we talked about the neurons earlier uh remember in this diagram here as you can see the three different types of neurons these neurons are usually the things uh of course they are a bit more specific these neurons are required in many in a lot of numbers to make up the nerve tissue so this is just the introduction of the nervous system now when we are talking about the nervous system we do need to know the types of neurons because neurons are these particular cells that are supposed to send or transmit or transfer the electrical impulse the signal right and we have three different types of neurons sensory neuron which comes from the word sense relay neuron which is to relay or to connect and Moto neuron Moto comes from the Latin word mover so what exactly are these neurons doing so to understand exactly what these neurons are doing we must go back to the example that I was talking about in the first video where you look at a piece of cake with your eyes and then your stomach will basically start to rumble and produce gastic juice so what's normally supposed to happen is light hits the cake and the light from the cake gets reflected into your eyes and your eyes have these structures known as photo receptors or just receptors that's fine and these receptors are supposed to detect the stimulus in this case they detect light it's as simple as that now what happens here is if you notice at the eye I'm drawing out a purple color line right and that is actually a neuron and that neuron is connected to the sensor or the receptor I use the word sensor but what I mean that is it's connected to the receptor so what neuron is that that neuron is referred to as the sensory neuron all right so what that neuron does is that neuron will i' I've put it as I've written it down as SN over there uh but in the exam you cannot write it down as SN you have to put the full name sensory neuron and I will talk about the function in a while but what am I drawing over over there in pink you can see that it's the brain and the spinal cord and at the bottom of the spinal cord I'm drawing out a green neuron over there from the inside of the spinal cord towards the stomach and that is MN which is the Moto neuron the Moto neuron is connected to the Mover or the effector which means to say in this case that is the stomach what do I mean by that okay let's talk about this so you see the sensory neuron and the motor neuron in this situation are quite far away so how's the sensory neuron supposed to communicate with the Moto neuron that hey there's cake in front of us we need to do something about it well that's when you have something called the relay or the connector and in the brain or and the spinal cord you have millions upon millions of these neurons called the relay neuron which I've represented in purple I don't know purple maroon magenta I don't know what that color is but you you get what I'm trying to say that okay and the relay neuron connects all the way and it Bridges the gap or the distance between the sensory neuron and the Moto neuron and once the signal reaches the Moto neuron the Moto neuron sends the signal to the stomach which is known as the eector and the eector is that part of the body that will produce the response in this case what is the response when you see cake you your stomach will growl and it produces the gastric juice the arrows in Orange are just the transmission of the nerve impulse or the electrical impulse as you can see there they start from the receptor they move along the sensory neuron towards the relay neuron towards the motor neuron and it hits the effector in the end so what is the function of the sensory neuron the function of the sensory neuron is to transmit impulses from the receptor to the relay neuron inside the central nervous system you can say relay neuron if you want to you can also say transmits impulses from receptor to CNS or central nervous system that's fine as well and what's the function of the relay neuron the function of the relay neuron is to transmit impulses from the sensory neuron to motor neurons because it Bridges the gap between the sensory and motor neuron as we can see in that diagram over there and of course the motor neuron what is their function their function is to transmit impulses from the CNS or the relay neuron you can say it like that towards the eector now you must understand something very important here if you notice I'm highlighting this in Orange the relay neurons are always only found in the central nervous system which means to say they're only found in within the brain and the spinal cord they are not found in any other parts of the body you cannot find it in your hand your toes your shoulders your head knees whatever okay the relay neuron is only specifically found in the central nervous system or the CNS so these are the particular functions of the neurons as you can see over here right so if you so if you go back to this particular diagram okay that that neuron so we have the stimulus the stimulus is detected by the receptor the receptor sends a signal through the what neuron is that that neuron is the sensory neuron right there and the sensory neuron transmits the impulse to the relay neuron and from the relay neuron it goes to the Moto neuron and then after that it goes to the eector you must know the appearance of the sensory relay and Moto neuron and in the next particular video we are going to be looking specifically at the structure of the sensory neuron and Moto neuron at least cuz that's quite important for the exam too