Neurology | Neuron Anatomy & Function

Alright ninja nerds, in this video today we're going to talk about the structure and

function

of

neuron

s. Alright guys, before we start this video, hit the like button, comment in the comment section and subscribe in the comment section as well. description box we have links to all of our social media platforms for you to interact with us alright ninja nerds let's get started alright ninja so the first thing we have to talk about when we talk about a

neuron

is obviously going over . the different structural components of a neuron, so what constitutes a neuron structurally, then we have to talk about what those different components of a neuron do, so first things first, when you take a look at this neuron, you see these little Extensions coming.

Of this big circular structure here, all these little extensions are called dendrites. That's the first thing I want you to know. The extensions that come out of this neuron are called dendrites. These are the receptive zone. We'll talk about what that means. For a neuron, the next thing is this big circular structure here with a bunch of stuff inside of it. This here is called the cell body or soma, so it is called the cell body or also sometimes known as soma, the third part here. of the actual neuron is this long, elongated portion that will be between the cell body and the axon terminal.

Well, this portion here is called the axon, so this third part here is called the axon. Now I have to add one. Smaller subcomponent of the axon is important because it's going to come up when we talk about action potentials. The part where the cell body narrows and enters a sort of thin structure of the axon is called the axon mound, so always remember that I'm looking at an axon like this, if I were to draw another small version like this, there's a part where the cell body starts to narrow, that portion where the cell body narrows like a funnel, this portion here is known as the axon hillock okay, so when you talk about the axon, a special part to remember is called the axon hillock.

The reason this area is important is because there is a high concentration of voltage-gated sodium channels there, so whenever action potentials are generated, they are generated here and move down the axon. Well, this last portion here of the neuron is this little kind of bulbous structure here of the neuron that comes out of the axon and this is called the axon terminal or synaptic terminal. write axon terminal and sometimes you might even hear it written as axon terminal bulb or synaptic bulb, there are a lot of different synonymous terms, okay, so we have all the different components of a neuron, first let's talk about what their

function

s are, so now we're going to start talking about the functions of these different areas of the neuron, so we talked about the dendrites, so what you want to think about here is that we're actually looking at one of these dendrites coming out okay. and we're Like we're going to cut this to the right and really zoom in on this view, so we're going to take this dendrite, we're going to take a section of that cell membrane and we're going to look at it here now.

Another thing to add is that I want you to imagine. This is what we are going to call our postsynaptic neuron, which means that there will be other neurons that will synapse with this postsynaptic neuron, so let's imagine here that there are other neurons interacting at that site that we are going to approach. When we get down to it, we have some proteins that you need to know because they are relevant to the function of the dendrite in this part of the dendritic cell membrane, they have these special types of channels, what are these special types of channels, these channels that They are present in dendrites they are called ligand gated ion channels and they are important because they are involved in the formation of epsps and ipsps what the heck is that zach?

I'll explain to you what that means, these neurons, imagine, here I have a kind of like a little neuron here like a little axonal extension and it's releasing a neurotransmitter, okay, what that neurotransmitter is going to do is come here and join this little pocket. Well, to this ligand-gated ion channel when it binds to the pocket there is normally like a little valve, so to speak, that blocks this opening for the ions to come in like this, but once this little neurotransmitter binds to that pocket, causes the fuel valve to open and then allows the positive ions to move into the cell, creating the cell is nice and positive, that's called depolarization when you make the cell more positive or less negative, for so to speak, and that's known as depolarization just when you make it more positive and that's called epsp, you're trying to stimulate the neuron to fire or generate an action potential and the other aspect let's say you have another neuron here maybe it's this one and you have the axon here and this axon is releasing another neurotransmitter but instead of this neurotransmitter being stimulatory we have the opposite, we have an inhibitory neurotransmitter and then that neurotransmitter binds to this little pocket in that ligand-gated ion channel, normally that channel has a valve that closes it so, when the neurotransmitter binds, it opens the valve if you will and allows negative ions to flow into the cell these negative ions make the inside of the cell more negative than usual, it takes it underneath of what is called resting membrane potential, which is called hyperpolarization and hyperpolarization when it makes the cell more negative than usual is called ipsp why is this important?

These terms together are called are involved in what are called graded potentials and these are basically small changes in the voltage of the cell membrane to basically try to get the cell to develop the ability to generate action potentials, so its dendrites are involved. in potential graduates. What I want you to know is that through these ligand-gated ion channels there is another way and it is important that you remember the second way. The second way that there are other proteins here that are involved here is through what is called the g protein. -coupled receptors we're not going to go through this mechanism because it's long and unnecessary, we have other videos that cover that, but these have g protein coupled receptors which again imagine you have a neuron here that releases a neurotransmitter that the neurotransmitter binds to this little receptive region of this pocket this jeep this receptor here when it binds to it activates what is called g protein and that g protein can activate what is called second messengers and these can be of several different types, but eventually that activates what is called protein kinases and The point here is that these protein kinases can phosphorylate particular proteins that are present in the cell membrane and perhaps this protein that is present in the cell membrane that is activated by these protein kinases, what that will do is allow the input of positive ions. flow by making a positive change causing an epsp or bringing negative ions into the cell and if those negative ions flow into the cell that could be causing an ipsp so it's the same concept just there is a different way they get there this is what Dendrites now not only perform this type of action that are involved in graded potentials, whether they are ligand-mediated or G protein-coupled cell bodies, they also do, that means that if you were to take a look and zoom in on that cell body and really look at it, everything that will happen there is happening here, it's the same type of activity, so you will also have neurons that will interact here, presynaptic neurons that will interact with the cell body, okay, that's one thing.

So one thing we already know is that this cell body is also involved in graded potentials, but it has an even more significant function. A very important function is involved in protein synthesis and when I talk about this we will literally go over the most basic ones. aspects of what I mean by protein synthesis, the process, but what I want you to know is that when we talk about protein synthesis, what kind of proteins are we making, there are proteins all over this damn cell, they could be neurotransmitters that actually you are synthesizing. be enzymes that are involved in particular cellular processes, they could be membrane proteins, perhaps membrane proteins that are going to be g protein-coupled receptors or voltage-dependent ligands, so they could be membrane proteins, so it is important that This cell body function that function, how all that happens, let's go over that briefly, so when we talk about protein synthesis, how all this happens, we understand the process of how it's involved in graded potentials that is basically designed to take potential of resting membrane to a threshold potential to trigger an action potential, we already talked about that, but how is it involved in this protein synthesis in the basic sense?

Here you have the DNA inside the nucleus of the cell body and that DNA can have particular genes. that are constantly expressed and maybe these proteins are for voltage-dependent proteins, for ligand-dependent proteins, maybe they are for neurotransmitter enzymes, whatever, but every time that gene is transcribed, we convert it into mRNA, that is called transcription , then the ARNM becomes, it does what it is then. exported out of the nucleus into the cytoplasm and then it gets to the next structure here, this next structure is found is called rough endoplasmic reticulum, but it's important to remember that the rough endoplasmic reticulum inside neurons is sometimes called Nissl bodies, okay, Sometimes you may hear the term Nissl bodies and this is basically a specialized name for the rougher neurons.

Now this mRNA can go to this rough endoplasmic reticulum and in the rough endoplasmic reticulum it will use that mRNA and then translate it into other words. we're going to turn this into a protein, okay, so we're going to turn it into a protein, that protein will then be packaged into the rough endoplasmic reticulum and then bud off to then be further modified and packaged by the Golgi apparatus, so here you are. It will be a small vesicle that will come out of the rough surface and will consist of proteins, then it will move to the Golgi apparatus and in the Golgi apparatus it will undergo modifications and then it will be packaged into vesicles where we are going to take that. protein and package it inside this vesicle and then sprout that vesicle from what is this structure here, this structure is called the Golgi apparatus, so this is your golgi now from here, when you sprout that gold from the golgi, you move that sprout vesicle that vesicle that contains proteins.

Let's assume that this protein that we are synthesizing here is actually a neurotransmitter. The neurotransmitters that are packaged in these vesicles have to be transported down the axon to that axon terminal and then we have to do that. We're going to talk about how the hell those vesicles that contain proteins and other things like organelles are transported down the axon to the axon terminal, so again we understand that this process of protein synthesis is what happens in the nucleus and this may not be just neurotransmitters, this could also be enzymes or membrane proteins. Okay, that's what I want you to know about the cell body.

Okay, now that we've talked about that, let's move on to the next part, which is the axon, so the axon is this long tube between the cell body and the axon terminal what is its function obviously almost anyone who is learning about this knows that the main function of the axon is to conduct action potentials and what an action potential is is a voltage usually a positive charge a flow of positive charge down the axon from the cell body down the axon to the axon terminal right where there is a flow of positive charge which is called depolarization, but what follows is usually a repolarizing wave, so when we talk about an action potential there is the depolarization wave and then there is the Repolarization Wave and we will go over that a little later. and we'll talk about what the heck that means, but that's the most important thing we know about the axon: it drives action potentials toward the depolarizing wave downward, toward a positive charge followed by a repolarizing wave. of negative charge, the next part is the one I really want to talk about because it's not often talked about, but it's clinically relevant.

You have this big blue structure in the middle that we're going to talk about, called microtubules, and on those microtubules are special types of proteins called motor proteins and these motor proteins are involved in transporting things up and down in axonal transport. of the axon, so this purple protein is actually known as kinesin and this kinesin is what's called a positive, directed motor protein. I don't really care about that, what I want you to know is that it moves things, we'll talk about what those things are from the cell body to the axon terminal, so when you go from the cell body to the axon terminal, that's what it means. as axonal transportanterograde to give you an idea of ​​what kind of things it would carry, we already talked about that.

This vesicle, which contains neurotransmitters, membrane proteins, enzymes, could have to transport it to the axon terminal to be able to release it or I can. connect it to the membrane down here or maybe I have to take a mitochondria here because I need a lot of ATP to be produced here to drive some of these processes, so it moves organelles, neurotransmitters and vesicles. In the opposite situation, you need that this little guy or friend take things in the opposite direction so this orange protein is called dynein and dynein is a less indirect motor protein and this takes things from the axon terminal and again it could be an axon I'm just giving you the direction that goes from the axon terminal towards the cell body and when you go in that direction it is called retrograde axonal transport, what kind of things would you like to transport?

So maybe the mitochondria have lived their good life and it's time for it to go well and it needs to be picked up and recycled or degraded, maybe you want to get some growth factors into the cell body, where the nucleus is, to stimulate the proteins that are involved. over there. you might need that, so that's what I want to talk about now is some of those things that it transports to and from and how it's clinically relevant, so what do we say the axon does? It conducts action potentials that we said if we go down there could be a positive flow of charge down the axon followed by a negative charge or a depolarizing wave followed by a repolarizing wave.

I want to briefly talk about that, we'll talk more about it in the video on the degree of rest and action. potentials but here in this cell membrane of these purple channels and we're going to refer to these channels that are here as these voltage-dependent sodium channels and these guys will open once you reach a particular voltage, a threshold voltage if you do it once that you reach that threshold voltage Sodium ions will then rush into this axon and when these positive ions rush into the axon, the cell, the actual cytoplasm here, it really makes the inside of the cell super positive and what you should think about is that you have a flow of positive charges. that are moving down this axon and that is where that depolarization or flow of positive charges that is involved in the depolarizing phase of the action potential comes from, on the other hand, you want the action potential after you have stimulated the axon In the terminal.

Now you need to relax or make this cell go into a resting state after it has been depolarized, so you need a negative charge to flow so the cell can rest. To do that, you need these garnet channels that are called voltage-gated potassium. channels and these will only open when you reach a particular threshold, usually after depolarization, once they open, potassium leaves the cell when potassium leaves the cell, what does that do? It makes the inside of the cell extra negative and Now, that negative charge, if you're jumping here step by step, that negative charge flows down the axon to the axon terminal and this is called a repolarizing wave, so that's the involvement of the axon, next is this transport.

The process here is your kinesin protein, so here's kinesis, we'll put a k here on your body, what are you transporting here? Well, imagine that you are transporting what that vesicle is and what type of vesicle that vesicle contains multiple things, proteins in general, right? maybe inside of this it contains neurotransmitters membrane proteins enzymes that we need down here maybe it's also transporting mitochondria because you also need mitochondria down there so maybe it's also transporting a mitochondria to the axon terminal in the opposite situation think about this , this guy, right? this is your dynein this is going to transport certain types of things back up here what type of things is it going to transport back up here maybe it's transporting vesicles or mitochondria that have lived their best life but it's time for them to go and in that situation we could be transporting vesicles containing that must be degraded or organelles that must be degraded or recycled.

The last situation is that I could be transporting something very, very important that I need you to remember we are going. To do this in orange so you don't forget, it could be transporting upwards, let's say for some reason there was some nerve injury or there is some damage to the nerve terminal or the axon itself and you want to tell the cell body that maybe there was some damage to the membrane, some damage to some of the proteins or something like that down here, so what this axon terminal will do is it will send through these proteins dynein nerve growth factors and this nerve growth factor as it is transported by The dyneins up here, what can they do?

They can then move up to the cell body in the nucleus and this nerve growth factor can stimulate particular genes to increase mRNA expression, increase mRNA translation, and increase protein packaging and production in vesicles. so that we can transport more vesicles here that contain more proteins or other different organelles to help repair or grow whatever is happening here in the terminal axon or in the distal axon is not so good, I think that is the last thing that you need. What kids need to know here is that pathogens love to plague these axonal transports. They know there is a virus called the polio virus or the rabies virus or the herpes simplex virus or the varicella zoster virus.

All of these viruses can basically infect the nerve endings of the nerve. terminals are going to try to migrate to the cell body because these are viruses, they need our nuclear machinery to generate more viral proteins and replicate. They can't do that down here when they infect the nerve terminal, so what they do is they travel with these motor proteins, these dyneins, and then they travel to the cell body and then this virus, if you will, can use our nuclear machinery to produce more viruses that destroy this neuron, you know, in a perfect example of how it goes the other way. direction, you know, when someone ever gets shingles, if they like the virus, the varicella zoster virus, they get infected, that virus travels here uses the nuclear machinery, but maybe it stays dormant for a couple of years and then , due to some immunosuppressive stress problem, that virus contracts. it activates and then it starts producing tons of viral particles and then it uses the protein kinesin to carry that virus back to the axon terminal and then from the axon terminal it is released into the skin tissue and what happens is it starts to damage skin tissue. and you can end up with shingles, so do you see how pathogens can actually use this axonal transport mechanism to their advantage in some way?

So I wanted us to know that okay, let's talk about the axon terminal. The next thing we need to talk about is the axon terminal. The axon terminal. I just want you to remember that this is the secretory region. What the hell does that mean that this is where neurotransmitters are released? Also, not only is it the area where neurotransmitters are released, it is also very, very important where there is a reuptake of the neurotransmitters that are involved here. I can't emphasize that the reuptake of particular neurotransmitters will apply very rapid clinical relevance to that, but now let's talk about how it's involved in the secretory region, how it's involved in the release of this neurotransmitter and then how it's involved in the reuptake and we talk about quick clinical relevance to that, so this depolarizing wave of action potentials due to these voltage-gated sodium channels that allow sodium influx. to rush and go down the axon to the axon terminal, that voltage stimulates these voltage-gated calcium channels, so these will be your voltage-gated calcium channels.

Now what happens is that once it's stimulated, calcium will rush into this axon terminal when calcium rushes into the axon terminal, there's a very important reason, you know, what's in these vesicles that we talk about, which consist of what neurotransmitters are inside the vesicle, they have particular proteins that are embedded in their vesicle membrane and in the plasma membrane of this axon terminal they are called trap proteins the trap protein that is present here in the vesicle is called traps v and if you really want to know they are called synaptobrevin and synaptotagmin the other one here in the actual cell membrane of the axon terminal is they are called t traps and they consist of syntaxin and snap25 if you really want to know that, but what happens is that calcium is the bridge between the v-traps and the t-trap, so once it gets in, it binds to these little v-traps and traps and acts as a liquid bond and pulls the vesicle towards the cell membrane and fuses the vesicle membrane with the plasma membrane of the terminal and what does that look like after, look at this, look at how cool it blends into it and it looks. so, once that happens now, all of these neurotransmitters that are located in the vesicle are now open to be released at the synapse and maybe at the synapse there is another neuron, maybe there is another neuron here and it has particular receptors present on that cell membrane to which that neurotransmitter will bind and carry out perhaps the same process that we have talked about up to this point.

Here is the important point once the neurotransmitter has exerted its effect on this other cell, whether it is another neuron, another muscle, any neurotransmitter. it has to be degraded or removed from that synapse and there are two main ways to remove neurotransmitters from a synapse, so the termination of neurotransmitters, if you will, is done in two ways, I consider here one is through reuptake and the other through degradation, so they have an enzyme in the synapse that degrades that neurotransmitter. The one that is really relevant here and that you need to know is this reuptake because that is where the axon terminal comes in, let's say that the neurotransmitter after binding with this receptor does its function and then What happens is that we have to return that neurotransmitter to this terminal of the axon to incorporate it back into this vesicle.

How we do? We use this reuptake protein. Then you use a reuptake protein present here to move that neurotransmitter back into the axon. terminal and then maybe from there it might have to go through a couple of enzymatic steps, but either way it will be returned to the vesicle and recycled. That is important. ¿Why is it so important? Let's say this neurotransmitter is serotonin. Sometimes written as 5-hydroxytryptamine. -ht the reuptake protein would be called serotonin reuptake protein if you give it a drug called s s r eyes selective serotonin reuptake inhibitors like zoloft lexapro all those things uh prozac are going to inhibit these reuptake proteins why is it so important now which neurotransmitter can?

It can be returned to this actual axon terminal and remains in this synapse continuously stimulating this cell which could be important whenever that excess 5-hydroxytryptamine is needed to improve mood in people with depression, anxiety, obsessive-compulsive disorders, for example. that's so important. It is important that you sometimes know the basic functions of these components of the neuron. Okay, that covers the axon terminal. So we talked about the basic structure and functions of the different parts of the neuron. Now what we have to remember is that when we talk about neurons and we could use a lot of this terminology during the process of all the

neurology

videos in our playlist, is that you need to know how neurons are classified less frequently, they are used in a structural classification more frequently, especially throughout everyone's process.

The videos that you are going to see will be a more functional classification that we are going to talk about, so to leave this part aside because it is a little boring, I am not going to lie to you, just talk about what these things are and where you can find them , so the first one here is this multipolar neuron, so let's write them down. This is your multipolar neuron and I'll explain why in a second this one is called bipolar. neuron, okay, this is called a bipolar knot and this last one here is called a pseudo unipolar neuron and I'll explain why all this and then we'll talk about where you can find them and why you would find them. they are there so multipolar neurons the reason they are called that is very simple look how many dendritic extensions I am growing out if I have more than three dendritic extensions coming out that is enough to call this a multipolar neuron multiple extensions dendritic with a cell body and an axon extension that is multipolar if I only see a dendritic extension, then we will put a dendritic extension and an axon coming from the cell body that is a bipolar neuron, it is not difficult, right, pseudounipolar is really strange, like this is.

It doesn't really have a dendrite and it doesn't really have a distinguishable axon with some kind of terminal, it has itsperipheral process, so here is the cell body. Well, here is the cell body. So you have this process coming from the cell body. It usually goes out to the periphery, so we call this the peripheral process and then we call this part of the cell body that goes to the central nervous system the central process. It's pretty simple. Well, now the important thing is to know where you can find these things. and why you would generally find them there mostly multipolar neurons.

Think about it. They have tons of dendrites. What does that mean? What do dendrites mean? They are the receptive region, so they have to receive signals from multiple neurons everywhere. about the primary motor cortex who has to receive information from because that is an example of a multipolar neuron would have to receive information from your basal ganglia your basal ganglia have to send information to your motor cortex you know you have your sensory cortex to send information to The motor cortex, you know that your cerebellum has to send information to your motor cortex, what else would send information there?

You also have other motor areas called the premotor cortex and your supplementary motor cortex would have to send information there, so it has to have all these receptive regions and then they have an axon that goes down to the spinal cord, which is an example of a neuron. multipolar. Multiple receptive regions with a descending axon. Same thing, this is literally the same concept of cerebellum, so obviously, if we were to give an example. here just choose the motor cortex as an example, the second example, choose your cerebellum and if we are really specific about what type of neurons you actually give these neurons in the motor cortex, they call them pyramidal cells and those cerebellum, we call them pyramidal cells.

Purkinje yes You really want to know I want you to understand the basic concept, where is the information? Multiple receptive regions. Your spinal cord picks up sensations. Proprioceptive sensation. Collect information about your balance from your inner ear. Collect information from your motor cortex about the particular. motor plan that you have to move all of that has to go to the cerebellum and then the cerebellum from there can send its information to tons of different areas, but you see how there are multiple receptive regions and then an axon extension that is an example of multipolar neurons. Bipolar neurons are really strange and you find them mainly in your special sensory organs, which ones the retina has bipolar neurons, which we actually talk about, and what they do, because they don't actually generate action potentials, they generate what are called graded potentials. , that's what we talked about. in our special senses special sensors playlist the other one is the olfactory epithelium which is present in the roof of the nasal cavity so also the factory nerves are also examples of bipolar neurons and one more is the inner ear in particular. like the vestibule and semicircular canals are also examples of bipolar neurons, so the best way to remember this is primarily your special sensory organs, that's really where you'll find bipolar neurons.

The last one is your pseudo unipolar, your pseudo unipolar is actually very important. I want you to remember this: the main area where you'll hear them tons and tons of times throughout the

neurology

playlist is the dorsal root ganglion, the dorsal root ganglion, which is located outside the spinal cord, so here we are going to be what is called the cell body, that part there has a peripheral process, we said well, that peripheral process can go to the skin, let's just put here skin, we are just going to write skin, collecting sensations of the skin, lowering it through this peripheral. process to where the cell body is, then to the central process and from here it can synapse somewhere in the spinal cord or go up to the brain.

Well, this is an example of the pseudounipolar neuron, but it is located outside the peripheral nerve. of the central nervous system and a group of cell bodies located outside the peripheral nervous system are called ganglia and since it is close to the dorsal root that is why we call it dorsal root ganglia. Okay, last but not least, certain cranial nerves have pseudounipolar neurons the classic classic example is cranial nerve five, cranial nerve five tested, what is your trigeminal nerve, your trigeminal ganglion, this is a perfect example, you know , there is a ganglion that is found inside here, like outside, inside the base of the skull, here and it has three divisions, one is called the ophthalmic division, a maxillary division and a mandibular division, but they capture sensations, all of them from the face, those Sensations travel through its peripheral processes to the cell body, from the cell body you have a central process that enters. from the central nervous system to the nucleus within the brain stem, which is the trigeminal nucleus, which is another example of a pseudounipolar neuron, all right, beautiful, that's the structural classification, let's go to the functional one, more important, so we talk about the structural classification of neurons.

Now let's talk about the one that you'll probably hear a lot about during our neurology lecture process, which is functional classification, so when we talk about neurons, they can be sensory neurons, motor neurons, or interneurons. What the hell does that do? I mean, I want to establish some terminology here so that the sensations can capture sensations from your viscera, maybe sensations from the lungs, from the heart, from the gastrointestinal tract, from the urogenital tract, those visceral sensations go from these organs to your central nervous system. real, in this case. brain or spinal cord, that's called afferent information, so sensory information is also known as afferent information, so you can have neurons that carry sensory information or afferent information to your central nervous system, but since it comes from the viscera, we give this a special term called general visceral afferent neurons, these are terms that will come up later in the lectures, okay, it's important to know that, one after another, you could be picking up sensations from your skin or your skeletal muscles or your joints, your ligaments. all those areas are somatic sensations, so when it is somatic it means that it comes from the skin, the joints of the muscles, when I refer to the muscle, I mean the skeletal muscle, well, the joints, the ligaments, that sensory information can be carried to the brain or spinal cord, but those are called general somatic afferent fibers.

Well, next you could have sensory information being conducted from your special sensory organs that will be responsible for vision and hearing if this travels to your actual central nervous system and comes from a very particular special sensory organ here, from the eyes. or ears, this is called special sensory afferent fibers, ssa fibers, it is okay, last but not least, if the sensations that are carried to the central nervous system and the information through these sensory neurons come from smell or taste and they go to the central nervous system. that is a special sense but it is more visceral, that is why it is called special visceral afferent neurons.

These are terms I want you to understand when they come up in future lectures. The next is motor neurons. The motor neurons are taking in efferent information, that means. they move away from the central nervous system and go to the effector organ here, in this case it could go to your visceral organs maybe the smooth muscle inside the respiratory bronchi maybe the cardiac muscle inside the heart maybe Let's see which ones will be present in different places, that type of information is autonomous information, but it is visceral and motor and moves away from the central nervous system, so these fibers will be motor fibers of the central nervous system. to the viscera for smooth muscle, cardiac muscle and gland activity are called general visceral efferent neurons, the motor neurons that go from the central nervous system to the effector organ, in this case, skeletal muscle, right skeletal muscle, This is a somatic function, so it is called general somatic. efferent neurons that carry motor information from the central nervous system to the skeletal muscles, last but not least, the ridiculous ones here love to give extra names to complicate everything for us, but there will be nerves that go to special muscles around the head and area of the neck which is carried by a pair of different nerves, cranial nerve 5, which is the trigeminal nerve, cranial nerve seven, which is the facial nerve, cranial nerve nine, which is the glossopharyngeal nerve, and cranial nerve 10, which is the vagus nerve, these will innervate the muscles of the head. and the neck region of a particular embryological thing called the pharyngeal arches and really the best way to remember them is to correlate them with the nerve, so cranial nerve five supplies the first pharyngeal arch, cranial nerve seven plus supplies the second pharyngeal arch and The glossopharyngeus supplies the third pharyngeal arch. and then the vagus innervates the fourth and sixth pharyngeal arches and again these are skeletal muscles but they are muscles that are basically a part of the head and neck that are derived from these embryological origins and that's why we don't call them general. somatic efferents we have to be complicated and call them special visceral efferent neurons, okay beautiful, let's move on to the last part, then the last functional classification of neurons is interneurons, it is literally what it sounds like, they are the neurons between the sensory neurons and the motor neurons that's all so I want you to think about this we have that motor cortex right up in the cerebral cortex in your frontal lobe this motor cortex will send its motor fibers down and technically it goes to the neurons in your spine right cord of neurons lower motor and that goes to the skeletal muscles, but this is the motor pathway, this whole red line is your motor pathway that comes from maybe the skin or maybe even from the muscle itself because it has receptors there as well.

They have these particular sensory receptors that are receiving information and when they come in this is your sensory fiber here it can stop at a particular neuron between the motor and the sensory now what is this? This is a particular core, we'll talk about this later in another video for now I just want you to think of it as a kind of relay neuron, so if this is a relay neuron, let's change the color here, let's make this green to so we know the difference here, this relay neuron can fire some action potentials to another relay neuron and then that relay neuron can fire some action potentials to this motor to the actual motor cortex, so think about this, it has its sensory fibers that are carrying sensations to your central nervous system and may be going up. and then leave some relay neurons that will then come back and stimulate your motor neurons.

You see how there's that thing in the middle here called interneurons to give you an idea so you can see I'm not making this stuff up. This we will talk about later is in the medulla, a part of the medial meniscus pathway of the dorsal column, this is called nucleus como gracilis and nucleus unaitus, so these will be two that you will talk about, it is an example of an interneuron. Your thalamus, you know, your thalamus has tons of different nuclei and it also has the ability to send its action potentials to the motor cortex, so it's important to realize that we're talking about interneurons.

These interneurons make up the majority of your central nervous system. and we commonly only refer to them in the spinal cord, but they are throughout the brain and brainstem, so to give you the classic example of an interneuron with the spinal reflex, it's pretty simple, think about this, you have a feeling that comes from the skin, someone touches your skin, that sensation then does what moves through the sensory neuron to the spinal cord, from there it acts on an interneuron, that internal neuron then sends information to your motor neuron and that motor neuron will send that information to the skeletal muscle to maybe make you move because maybe you pricked your finger on something that hurt and you had to move it away so you can see how the interneuron is involved between that pathway.

This is the classic situation, but also remember that it is present up here. in that brain and brainstem, okay, so those are the internal neurons and that covers neurons in general, okay, okay, nizhner, so in this video we talk about the structure and function of neurons. I hope that made sense. I hope you liked it. We thank you, we thank you for being awesome ninja nerds as always, until next time.