Transcript for:
Structure and Function of Neurons

all right ninja nerds in this video today we're going to talk about the structure and function of neurons all right guys before you guys get started in this video please hit that like button comment down in the comment section and please subscribe also down in the description box we have links to all our social media platforms for you guys to interact with us all right ninja nerds let's get started all right ninja so the first thing that we have to talk about when we're talking about a neuron is obviously go over the different structural components of a neuron so what makes up a neuron structurally then we got to talk about what those different components of a neuron do all right so first things first when you take a look at this neuron you see these little these little extensions coming off of this big circular structure here all these little extensions are called dendrites that's the first thing i want you to know so the extensions that are coming off of this neuron is called your dendrites these are the receptive zone we'll talk about what that means for a neuron next thing you have this big circular structure here with a whole bunch of stuff inside of it this here is called your cell body or your soma so this is called the cell body or also sometimes referred to as the soma the third part here of the act of the actual neuron is this long elongated portion here that's going to be in between the cell body and the axon terminal okay this portion here is called your axon so this third part here is called your axon now i have to add in one more little sub component of the axon it's important because it's going to come up when we talk about action potentials the part where the cell body kind of like narrows and goes into this kind of like thin axon structure is called the axon hillock so remember whenever you're looking at an axon like this if i were to draw another small version of it like this there's a part where the cell body starts to narrow that portion where the cell body kind of like narrows like a funnel this portion here is referred to as the axon hillock okay so when you're talking about the axon a special part to remember is called the axon hillock the reason why this area is important is because there's a high concentration of voltage-gated sodium channels there so whenever action potentials are generated they're generated here and move down the axon okay this last portion here of the neuron is this little kind of bulbous like structure here of the neuron coming off the axon and this is called the axon terminal or the synaptic terminal i'm just going to write axon terminal and sometimes you might even hear it written as axon terminal bulb or synaptic bulb there's a bunch of different synonymous terms there okay so we got all the different components of a neuron let's talk about what their functions are first all right so now let's go to start talking about the functions of these different areas of the neuron right so we talk about the dendrites right so what you want to think about here is that we're actually looking at one of these dendrites here coming off right and we're kind of going to cut into this right and really zoom in on it in this view so we're taking this dendrite taking a section of that cell membrane and looking at it here now another thing to add on to that is i want you to imagine this is what we're going to call our postsynaptic neuron that means that there's going to be other neurons that are synapsing on this postsynaptic neuron so let's imagine here that you have other neurons interacting at that site that we're going to zoom in on when we zoom in on that we got some proteins that you guys need to know because they're relevant to the function of the dendrite in this dendritic cell membrane part you have these special types of channels what are these special types of channels these channels that are present on the dendrites are called your ligand gated ion channels and these are important because they are involved in formation of epsps and ipsps what the heck is that zach i'll explain to you what that means these neurons right imagine here i have kind of like a little neuron here like a little axonic extension and it's releasing out a neurotransmitter okay that neurotransmitter what it's going to do is is it's going to come here and bind into this little pocket okay on this ligand-gated ion channel when it binds onto the pocket there's normally like a little valve if you will that's blocking this opening for ions to come in like this but once this little neurotransmitter binds onto that pocket it causes that valve fuel to open up and then allows for positive ions to move into the cell making the cell nice and positive that's called depolarization when you make the cell more positive or less negative if you will and that is referred to as a depolarization right when you make it more positive and that's called an epsp you're trying to stimulate the neuron to fire or generate an action potential and the other aspect let's say that you have another neuron over 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 let's have the opposing let's have an inhibitory neurotransmitter and then that neurotransmitter binds into this little pocket on that ligand-gated ion channel normally that channel has a valve that's closing it like this when the neurotransmitter binds it opens up the valve if you will and allows for negative ions to flow into the cell these negative ions make the inside of the cell more negative than it usually is it brings it below what's called resting membrane potential that's called hyperpolarization and hyperpolarization when you make the cell more negative than it usually is is called an ipsp why is this important because these terms collectively are called are involved in what's called your graded potentials and these are basically little changes in the voltage of the cell membrane to basically try to get the cell to develop the ability to generate action potentials so your dendrites are involved in graded potentials that's what i want you to know how via these ligand-gated ion channels there is another way though and it's just important for you to remember the second way the second way that it has other proteins here that are involved here is via what's called g-protein-coupled receptors we're not going to go through this mechanism because it's long and it's unnecessary we have other videos that cover that but these have g protein couple receptors that again imagine you have a neuron here releases a neurotransmitter that neurotransmitter binds onto this little receptive region of this pocket this jeep this uh receptor here when it binds onto it activates what's called a g protein and that g protein can activate what's called second messengers and these can be a bunch of different types but eventually that activates what's called protein kinases right and the whole point here is that these protein kinases can go and phosphorylate particular proteins that are present on the cell membrane and maybe this protein that's present on the cell membrane that's activated by these protein kinases right what that will do is that allow for either positive ions to flow in making a positive change bringing about an epsp or bringing in negative ions into the cell and if those negative ions flow into the cell that could be causing a ipsp so it's the same concept just a different way that they get there this is what dendrites do now not only do dendrites perform this type of action which are involved in graded potentials whether it be ligand-gated mediated or g-protein-coupled mediated cell bodies also do that so that means if you were to take a look and zoom in on that cell body and really look at it everything that's going to be happening there is happening here it's the same type of activity so you also will have neurons which are going to be interacting here presynaptic neurons interacting with the cell body okay so that's one thing so one thing we already know is that this also this cell body is involved in graded potentials but it has an even more significant function very important function it's involved in protein synthesis and when i talk about this we'll go over those literally the most basic aspects of what i mean by protein synthesis the process but what i want you to know is when we talk about protein synthesis what type of proteins are we making there's proteins all across this dang cell it could be neurotransmitters that you're actually synthesizing it could be enzymes that are involved in particular cellular processes it could be membrane proteins maybe membrane proteins that are going to be voltage-gated ligand-gated or g-protein-coupled receptors so it could be membrane proteins so it is important that this cell body perform that function how does all of that happen we're going to briefly go through that all right so when we talk about protein synthesis how is all of this happening we understand the process of how it's involved in the graded potentials which is basically designed to take resting membrane potential to a threshold potential to trigger an action potential right we 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 right and that dna may have particular genes that are constantly expressed and maybe these proteins are for voltage-gated proteins for the ligand-gated maybe it's for neurotransmitters enzymes whatever but whenever that gene is transcribed we convert that into mrna right that's called transcription that mrna is then done it does what it's then exported out of the nucleus and into the cytoplasm and then comes to this next structure here this next structure encounters is called the rough endoplasmic reticulum but it's important to remember that the rough endoplasmic reticulum inside of neurons is sometimes referred to as nissl bodies okay so sometimes you might hear the term nissl bodies and this is basically a specialized name for the rough er in neurons now this mrna may go to this rough endoplasmic reticulum and at the rough endoplasmic reticulum it'll use that mrna and then translate it in other words it's going to turn this into a protein okay so it's going to turn that into a protein that protein will then be packaged in the rough endoplasmic reticulum and then budded off to then be modified and further packaged by what else by the golgi apparatus so then here's you're going to be a little vesicle coming off of the rough er consisting of the proteins it'll then move into the golgi apparatus and in the golgi apparatus it'll undergo modification and then packaging into vesicles where we're going to take that protein and package it inside of this vesicle and then bud that vesicle off of what is this structure here this structure is called your golgi apparatus right so this is your golgi now from here when you bud that gold off the golgi you budge that vesicle off the bud that vesicle off which contains in it proteins let's just pretend that this protein that we're synthesizing here is actually a neurotransmitter neurotransmitters that are packaged into these vesicles have to be transported down the axon to that axon terminal and we have to next we're going to talk about how in the heck do those vesicles containing proteins and other things like organelles get transported down the axon to the axon terminal so again we understand that this protein synthesis process is what is occurring in the nucleus and this may not just be neurotransmitters this could also be enzymes or membrane proteins okay that is 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 this long tube between the cell body and the axon terminal what is its function obviously pretty much anybody who's learning about this knows that the primary function of the axon is to conduct action potentials and what is an action potential it's 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's a flow of positive charge that's called the depolarization but then following that is usually a repolarizing wave so when we talk about an action potential there's the depolarization wave and then there's the re-polarization wave and we'll go over that a little bit later and talk about what the heck that means but that's the big thing we know about the axon is it conducts action potentials right depolarizing wave down a positive charge followed by a repolarizing wave of negative charge the next part is the one that i actually really want to talk about because it's not often talked about but it's clinically relevant is you have this big old 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 the axon axonal transport so this purple protein is actually referred to as kinesin and this kinesin is a what's called a positive and 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 those are from the cell body down to the axon terminal so when you go cell body to the axon terminal that is referred to as anterograde axonal transport to give you an idea of what kind of things this would be transporting we already talked about it this vesicle containing neurotransmitters membrane proteins enzymes i might have to transport that down to the axon terminal so i can release it or i can plug it into the membrane down here or maybe i've got to take a mitochondria down here because i need a lot of atp to be produced down here to drive some of these processes so it's moving organelles neurotransmitters and vesicles down in the the opposite situation you need this little dude or dudette to be taking things in the opposite direction so this orange protein is called dynein and dynein is a minus indirected motor protein and this is taking things from the axon terminal and again it could be an axon i'm just giving you the direction going from axon terminal towards the cell body and this when you're going in that direction is called retrograde axonal transport what kind of things would you want to be transporting then maybe the mitochondria has lived its fine life and it's time for it to go okay and it needs to be taken up and either recycled or or degraded maybe you want to bring up some growth factors up to the cell body to where the nucleus is to stimulate proteins that are involved there we might need that so that's what i want to now talk about is some of those things that it carries to and from and how it's clinically relevant all right so what do we say the axon does it conducts action potentials which we said if we're going 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're going to talk about it more in the video on resting graded and action potentials but here on this cell membrane of these purple channels and let's refer to these channels that are on here as these voltage gated sodium channels and these guys will open once you hit a particular voltage a threshold voltage if you will once you hit that threshold voltage the 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 you want to think about this is that you have a flow of positive charges that are moving down this axon and that is where that depolarizing or flow of positive charges are coming from that's involved in the depolarizing phase of the action potential on the other hand you want the action potential after you've stimulated the axon in the terminal you need to now relax or cause this cell to go into a resting state after it's been depolarized so you need a negative charge to flow across so that the cell can rest in order to do that you need these maroon channels which are called your voltage gated potassium channels and these are only going to be open when you hit a particular threshold usually after depolarization once they open potassium floods out of the cell when potassium floods out of the cell what does that do it causes the inside of the cell to become extra negative and now that negative charge if you're kind of skipping along here step by step by step that negative charge is flowing down the axon to the axon terminal and this is called the repolarizing wave so that's the involvement of the axon the next thing is this transport process here is your kinesin protein right so here's the kinesis we'll put a k right here in his body what is he transporting down here well imagine he's transporting what that vesicle and what kind of vesicle that vesicle that's containing multiple things proteins in general right and maybe inside of this it's containing neurotransmitters membrane proteins enzymes that we need down here maybe it's also transporting mitochondria because you need mitochondria down there as well so maybe it's also transporting a mitochondria down to the axon terminal in the opposite situation think about this this guy right this is your dynein this is going to be transporting certain types of things back up here what kind of things is it going to be transporting back up here maybe it's transporting any 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 up vesicles that contain that need to be degraded or organelles that need to be degraded or recycled the last situation is it could be carrying up something very very important that i need you guys to remember we're going to do this in orange so you don't forget it it could be carrying upwards let's say that for some reason there was some nerve injury or there's 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'll send up through these dynein proteins nerve growth factors and this nerve growth factor as it's transported by the dyneins up here what can it do it can then go up to the cell body in the nucleus and this nerve growth factor may stimulate particular genes to increase the expression of mrna increase the translation of the mrna and increase the packaging and production of proteins in vesicles so that we can transport down here more vesicles containing more proteins or other different organelles to help to repair or grow whatever's going on down here at the axon terminal or distal axon isn't that cool i think it is the last thing that i need you guys to know here is that pathogens love to plague these axonal transports you know there's a virus called the polio virus or your rabies virus or your herpes simplex virus or your varicella zoster virus all of these viruses they can basically infect your nerve terminals from the nerve terminals they're going to try to migrate up 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 is they hitch a ride with these motor proteins these dyneins and then they travel upwards towards the cell body and then this virus if you will can then use our nuclear machinery to make more viruses destroying this neuron you know in a perfect example of it going the opposite direction you know when someone ever gets um shingles right if they get like the virus the varicella zoster virus they get infected that virus travels up here uses the nuclear machinery but maybe it lays dormant for a couple years then from some stress immunosuppressive issue that virus gets activated and then it starts producing tons of viral particles and then it uses the kinesin protein to bring that virus back down to the axon terminal and then from the axon terminal it gets released out to the skin tissue and what happens it starts damaging the skin tissue and you can end up with shingles so do you see how pathogens can really kind of use this axonal transport mechanism to their advantage in a way all right so that's why i wanted us to know that all right let's talk about the axon terminal all right so the next thing that we have to talk about is the axon terminal the axon terminal i just want you to remember that this is the secretory region what in the heck 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 the re-uptake of neurotransmitters that are involved here i can't stress that enough the re-uptake of particular neurotransmitters will apply a very quick clinical relevance to that but now let's talk about how it's involved in the secretory region how it's involved in this neurotransmitter release and then how it's involved in reuptake and talk about a quick clinical relevance to that so this depolarizing wave of action potentials because of this voltage-gated sodium channels that are allowing for sodium to rush in and move down the axon to the axon terminal that voltage stimulates these voltage-gated calcium channels so this is going to be your voltage-gated calcium channels now what happens is once this is stimulated calcium will rush into this axon terminal when calcium rushes into the axon terminal there's a very significant reason you know what's on these vesicles that we talked about which were consisting of what neurotransmitters in there right consisting within the vesicle they have particular proteins that are embedded on their vesicular membrane and on the plasma membrane of this axon terminal these are called snare proteins the snare protein that's present here on the vesicle are called v snares and if you truly want to know it they're called synaptobrevin and synaptotagmin the other one here on the actual cell membrane of the axon terminal is called your t snares and this is consisting of syntaxin and snap25 if you truly want to know that but what happens is is that calcium is the bridge between the v snares and the t snare so once it comes in it binds to these little v snares and t snares and acts as a liquid linkage and pulls the vesicle to the cell membrane and fuses the vesicular membrane with the plasma membrane of the terminal and what does that look like afterwards look at this look at how cool this is fuses with it and it looks like this once that happens now all of these neurotransmitters which are located in the vesicle are now open to be released out in the synapse and maybe out in the synapse is another neuron right maybe there's another neuron out here and it has particular receptors present on that cell membrane that that neurotransmitter will go and bind to and carry out maybe the same process we've talked about to this point here's the important point once that neurotransmitter has exerted its effect on this other cell whether that be another neuron another muscle whatever that neurotransmitter has to be degraded or taken out of that synapse and there's two main ways that you remove neurotransmitters from a synapse so neurotransmitter termination if you will is done by two ways i consider here one is by re-uptake and the other one is by degradation so you have an enzyme sitting in the synapse that degrades that neurotransmitter the one that's really pertinent here that you guys need to know is this reuptake because that's where the axon terminal comes in let's say that neurotransmitter after it binds with this receptor it does its function then what happens is we have to get that neurotransmitter back into this axon terminal to incorporate it back into this vesicle how do we do that we use this reuptake protein so you use a re-uptake protein present here to move that neurotransmitter back in to the axon terminal and then maybe from there maybe it has to go undergo a couple enzymatic steps but either way it'll get put back into the vesicle and recycled that's important why is that important let's say this neurotransmitter is serotonin sometimes it's written as 5-hydroxytryptamine 5-ht the reuptake protein would be called a serotonin reuptake protein if you give a drug called s s r eyes selective serotonin reuptake inhibitors like zoloft lexapro all of those things uh prozac those are going to inhibit these reuptake proteins why is that important now that neurotransmitter can't be brought back into this actual axon terminal and it sits out in this synapse continuously stimulating this cell that could be important whenever that excess 5-hydroxytryptamine is needed to improve mood in people with depression anxiety obsessive-compulsive disorders so that's why this is so important that you know sometimes the basic functions of these components of the neuron all right that covers axon terminal all right 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 might use a lot of this terminology throughout the process of all the neurology videos in our playlist is that you have to know how the neurons are classified less commonly they're used in a structural classification more commonly especially throughout the process of all the videos that you guys are going to watch it's going to be more functional classification that we're going to talk about so to get this part out of the way because it is a little boring i'm not going to lie to you let's 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 just write these out this is your multi-polar neuron and i'll explain why in a second this one here is called your bipolar neuron okay this is called your bipolar knot and this last one over here is called your pseudo unipolar neuron and i'll explain why all of this and then we'll talk about where you can find them and why that why you'd be finding them there so the multipolar neurons the reason they're called that it's very simple look at how many dendritic extensions i have coming off if i have three plus dendritic extensions coming off that's enough for me to call this a multipolar neuron multiple dendritic extensions with a cell body and an axon extension that's a multipolar if i only see one dendritic extension so one dendritic extension we'll put de and one axon coming from the cell body that's a bipolar neuron it's not hard right pseudo-unipolar is really weird it doesn't really have a dendrite and it doesn't really have like a distinguishable axon with a terminal kind of thing it has here your peripheral process so here's the cell body okay here's the cell body of it then you have this process coming from the cell body usually out to your periphery so we call this the peripheral process and then this part from the cell body going towards the central nervous system we call this part the central process so pretty straightforward okay now the important thing is to know where you can find these things and why you would generally find them there for the most part multipolar neurons think about it they have tons of dendrites what does that mean what does dendrites do they're the receptive region so they have to receive signals from multiple neurons all over the place think about the primary motor cortex who does he have to receive information from because that's an example of a multipolar neuron he would have to receive information from your basal ganglia your basal ganglia they have to send information to your motor cortex you know your sensory cortex it has to send information to the motor cortex you know your cerebellum it has to send information to your motor cortex what else would send information there you also have other motor areas which called your pre-motor cortex and your supplementary motor cortex would have to send information there so it has to have all these receptive regions and then have a axon that goes down to your spinal cord that's an example of a multipolar neuron multiple receptive regions with an axon going down same thing this is literally the same concept your cerebellum so obviously if we were to give an example here just pick motor cortex as one example the second example pick your cerebellum and if we're really being specific about what type of neurons they actually give these neurons in the motor cortex they call them pyramidal cells and those cerebellum we call them purkinje cells if you truly want to know that i want you to get the basic concept though where is the information multiple receptive regions your spinal cord picking up sensations proprioceptive sensation picking up information about your equilibrium from your inner ear picking up 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's multiple receptive regions and then an axon extension that's an example of multipolar neurons bipolar neurons are really weird and you find these mainly in your special sensory organs which ones the retina has bipolar neurons we talk about really where like what they do because these don't really generate action potentials they generate what's called graded potentials we talk about that in our special sensors special senses playlist the other one is your olfactory epithelium which are present in the the roof of the nasal cavity so the uh also the ol factory nerves they're also examples of bipolar neurons and then one more is your inner ear particularly like the vestibule and the semicircular canals are also example of bipolar neurons so best way to remember this is mainly your special sensory organs is really where you'll find bipolar neurons the last one is your pseudo unipolar your pseudo unipolar is actually very important i really want you to remember this one the main area where you're going to hear them tons and tons and tons of times throughout the neurology playlist is your dorsal root ganglion your dorsal root ganglion which is located outside of your spinal cord so here is going to be what's called the cell body that part there it has a peripheral process we said right that peripheral process may be going to the skin let's just put here skin we're just going to write skin picking up sensations from the skin taking it down this peripheral process to where the cell body is then into the central process and from here it may synapse somewhere in your spinal cord or go up to your brain okay so this is an example of the pseudo-unipolar neuron but it's located outside of the peripheral nerve outside of the central nervous system and a bunch of cell bodies located outside of the peripheral nervous system are called a ganglia and since it's near the dorsal root that's why we call it a dorsal root ganglia all right beautiful last but not least is certain cranial nerves have pseudo-unipolar neurons classical example classical is cranial nerve five the cranial nerve five tried which is your trigeminal nerve your trigeminal ganglion this is a perfect example you know there's a ganglia that sits here inside kind of like outside within the skull base here and it has three divisions one is called a ophthalmic division a maxillary division and a mandibular division right but they're picking up sensations all from the face those sensations travel down their peripheral processes to the cell body from the cell body you have a central process that goes into the central nervous system to the nucleus inside of your brainstem which is your trigeminal nucleus that's another example of a pseudo-unipolar neuron all right beautiful that's the structural classification let's hit the functional more important one all right so we talked about the structural classification of neurons now let's talk about the one that you're probably going to hear a lot of throughout the process of our neurology lectures which is the functional classification so when we talk about neurons they can be sensory neurons motor neurons or interneurons now what the heck does that mean i want to establish some terminology here so sensations it can pick up sensations from your viscera maybe sensations from the lungs from the heart from the git from the urogenital tract those visceral sensations are going from these organs to your actual central nervous system in this case the brain or the spinal cord so that's called afferent information so sensory information is also referred to as afferent information so you can have neurons that are taking sensory information or afferent information to your cns but since this is coming from the viscera we give this a special term which is called general visceral afferent neurons this is terms that will come up later in the lectures okay it's important to know that one the next one is you could be picking up sensations from your skin or from your skeletal muscles or from your joints your ligaments all of those areas this is somatic sensation so when it's somatic meaning it's coming from skin muscle joints when i mean muscle i mean skeletal muscle okay joints ligaments that sensory information can be taken to your brain or spinal cord but that is called general somatic afferent fibers okay next one you could be having sensory information being conducted from your special sensory organs which are going to be responsible for vision and hearing if this is traveling towards your actual central nervous system and it's coming from a special sensory organ very particular here from the eyes or ears this is called special sensory afferent fibers ssa fibers okay last but not least if the sensations that are being taken to your central nervous system affair and information through these sensory neurons are coming from your smell or from taste and going to your central nervous system that is a special sense but it's more visceral so it's called special visceral afferent neurons so these are terms that i want you to understand whenever they come up in future lectures all right the next one is the motor neurons motor neurons are taking efferent information that means they're going away from the central nervous system and going to the effector organ here in this case it could be going to your visceral organs maybe it's going to the smooth muscle within the respiratory bronchi maybe it's going to the cardiac muscle within the heart maybe it's going to glance which are going to be present all in different places that type of information is autonomic information but it's visceral and it's motor and it's going away from the central nervous system so these fibers that are going to be motor fibers from central nervous system to viscera for smooth muscle cardiac muscle and gland activity is called general visceral efferent neurons the motor neurons that are going from the central nervous system away towards the effector organ in this case skeletal muscle right skeletal muscle this is somatic function so this is called general somatic efferent neurons which are taking motor information from the central nervous system to skeletal muscles last but not least the ridiculous ones here they love to give extra names to make everything complicated for us but there's going to be nerves that go to special muscles around the head and neck area that are carried by a couple different nerves cranial nerve 5 which is your trigeminal nerve cranial nerve seven which is your facial nerve cranial nerve nine which is your glossopharyngeal nerve and cranial nerve 10 which is your vagus nerve these will supply muscles of the head and neck region from a particular embryological uh thing called your pharyngeal arches and really the best way to remember them is correlating with the nerve so cranial nerve five supplies the first pharyngeal arch cranial nerve seven plus supplies the second pharyngeal arch glossopharyngeal supplies the third pharyngeal arch and then the vagus supplies the fourth and the sixth sixth pharyngeal arch and again these are skeletal muscles but they're muscles that are basically a part of the head and neck that are derived from these embryological origin and so we don't call them general somatic efferents we got to be complicated and call them special visceral efferent neurons all right beautiful let's move on to the last part all right so the last functional classification of neurons is interneurons it's literally what it sounds like it's the neurons between the sensory neurons and the motor neurons that's it so i want you to think think about this we have that motor cortex right up in the uh the cerebral cortex in your frontal lobe this motor cortex is going to send its motor fibers down and it technically goes to neurons in your spinal cord right lower motor neurons and that goes out to your skeletal muscles right but this is the motor pathway this entire red line is your motor pathway coming from maybe the skin or maybe even from the actual muscle itself because you have receptors there as well you can have these particular sensory receptors that are taking information in and when they go in this is your sensory fiber here it may stop off on a particular neuron in between the motor and the sensory now what is this one this is a particular nucleus we'll talk about later in another video for right now i just want you to think about it as just kind of a relay neuron so if this is a relay neuron let's actually switch the color here let's make this green so we know the difference here this relay neuron may fire some action potentials to another relay neuron and then that relay neuron may fire some action potentials to this motor to the actual motor cortex right so think about this you have your sensory fibers which are taking sensations into your central nervous system they may be going up and then dropping off on some relay neurons which will then go back and stimulate your motor neurons you see how that's in between here that's called your interneurons to give you kind of an idea so that you can see that i'm not making these things up this later we'll talk about is in the medulla a part of your dorsal column medial meniscus pathway this is called your nucleus like gracilis and nucleus cunaitus right so these are going to be two that you'll talk about that's 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 as well so it's important to realize that we're talking about interneurons these interneurons make up most of your central nervous system and commonly we only refer to them into the spinal cord but they're all throughout that brain and brain stem baby so to give you the classic example of an interneuron with the spinal reflex it's pretty straightforward think about this you have a sensation coming from the skin someone touches your skin that sensation then does what it moves via the sensory neuron into the spinal cord from that it acts on a interneuron that intern neuron then sends information to what to your motor neuron and that motor neuron will send that information out to the skeletal muscle to maybe cause you move because maybe you pricked your finger off of something it hurt and you had to move it away so you see how the interneuron is involved in between that pathway this is the classic situation but also remember that it's present up here in that brain and brainstem baby all right so that's the intern neurons and that covers neurons in general all right all right nizhner so in this video we talk about the structure and function of neurons i hope it made sense i hope that you guys liked it guys we thank you appreciate you for being awesome ninja nerds as always until next time [Music] you