Neurology | Vestibulocochlear Nerve | Cranial Nerve VIII: Auditory Pathway

iein engineers in this video we are going to talk about the auditory pathway so if you remember we said that there was two parts of the vestibular cochlear nerve or cranial nerve eight there's the auditory branch or specifically we should actually call it the cochlear branch of the vestibular cochlear nerve and then there's the vestibular branch of the vestibulocochlear nerve in this video we're gonna talk specifically about the actual cochlear branch of the vestibular cochlear nerve all the destinations all the different types of circuitry that it's going through from the inner ear all the way up to the primary auditory cortex all right so let's go ahead and get started so if you guys haven't already please go watch our video on the cochlea where we talk about the actual spiral organ of Corti because i'm not going to go into the entire mechanism okay what we're gonna do is we're gonna take the scenario of hearing something right so I'm speaking right so when I'm speaking I'm producing sound waves right those sound waves what happens with them well if you remember we said it starts with the Oracle or the pinna right so it's your ear right the outer ear what does it do it funnels the sound waves into a nice little tube what is this tube call the external acoustic meatus from there it hits a connective tissue structure called the tympanic membrane the tympanic membrane will then vibrate all right it can compress and decompress when it does that it shakes some little bones inside of the ear right in these bones in order is going to be malleus right then you have incus and then you have the next one which is actually going to be called stay peas and what is these guys do so once you actually vibrate the tympanic membrane it vibrates the little ossicles malleus incus stapes stay p starts tapping on the oval window and if you remember the oval window was connected to that nice cochlear structure okay which caused the fluid-filled vibrations so now if we come over here let's pretend that this part here is the oval window and this one down here is the round window and who was tapping here stay please stay Pease was causing fluid-filled vibrations through the skaila vestibuli and then what happens is depending upon the frequency or the amplitude of the actual sound waves it can cause vibrations within this bacilli membrane which is a part of the skaila media also you can call it the cochlear duct but we said if the frequencies is not going to be high enough right then it can go past the actual cochlear duct at the helical trauma and then come down through the skaila tamp an eye and it can push on the round window right so we said that but let's assume that the sound frequency and the amplitude is enough to stimulate the actual vasila membrane and cause it to vibrate if it vibrates then what happens we said that when the bacilli membrane vibrates it causes these little hair cells to move right and these little hair cells they have specialized structures on their apical membrane what is those called they're called stereo cilia we said if the stereocilia beat towards the kind of psyllium due to them sharing across this red membrane which is called the tectorial membrane right so if the actual stereocilia beat towards the big one called the kind of psyllium it'll cause them to depolarize if it depolarizes it'll stimulate the release of a neurotransmitter onto these aether and nerve endings which is called glutamate okay so now if you remember we talked about this in the video on the cochlea there was a ganglion alright there was this ganglion right here this is that pseudo unipolar neuron right has a cell body with two processes one process is going out to the hair cells they call that the peripheral process the other one is going into the central nervous system that's the central process what is the name of this gang line if you remember was called the spiral gangly on and that should make sense because it's going to innervate the spiral ganglion okay the the order of the spiral organ of Corti all right so it's the spiral ganglion is intubating the actual spiral organ of Corti now peripheral processes going out to that organ of Corti where the hair cells are central processes go into the central nervous system now I'm just drawing one of these actual ganglion but imagine for a second that I have multiple of them so let's say here I have again here's a peripheral process here's a central process from this gangling let's say have another one here and here's a peripheral process here's a central process I'm gonna have hundreds and hundreds of these guys coming together and whenever they come together they're gonna make a specific branch they call this branch here the cochlear branch of the vestibulocochlear nerve so this is the cochlear branch of cranial nerve eight which is the vestibulocochlear nerve because there's two branches you know the cochlear branches which is coming from the cochlea picking up sound waves and the vestibular branch which is coming from the actual vestibule and the semicircular canals picking up static and dynamic equilibrium now this cochlea branch of the vestibular cochlear nerve he's gonna start moving we're only going to focus on the cochlear branch in this video right so what happens is this guy starts moving towards it the actual pons medulla Junction but in order for him to be able to get there he has to go through a hole within the skull so there's a hole within the skull specifically right around the actual temporal region okay the actual temporal region or the petrous part of the temporal bone there's this homeless skull and they call this hole the internal acoustic meatus or canal now there's another nerve that actually runs through there if you want to know there's actually the seventh cranial nerve so there's another nerve who actually does run within this hole here and this nerve is actually called the facial nerve cranial nerve seven okay so there is another nerve that actually runs within the internal acoustic meatus so now what have we gotten to first point here we have a stimulation of the hair cells second point we activate the peripheral processes of the spiral ganglia third part we're activating the actual central processes of the spiral ganglion eventually all these axons of the spiral nganga and come together and form the cochlea branch of the vestibular cochlear nerve it then runs through the petrous part of the temporal bone specifically through a hole there called the internal acoustic meatus with another nerve going with it alright and this is going to be the facial nerve once it actually reaches this pons medulla junction here it comes to specific nuclei okay it comes to specific nuclei located within the pons medulla junction specifically in the upper medulla alright there's a whole bunch of nuclei here this nuclei as a group let's pretend that I kind of circle all of these nuclei here I'm gonna circle all of these nuclei these nuclei are called my cochlear nuclei okay but what happens is we actually separate it into two parts okay so these blue ones here these blue ones these dark blue ones this is going to be the anterior or ventral cochlear nucleus okay so this ones up here are gonna be the anterior or the ventral cochlear nuclei okay the one in the back is going to be the dorsal or the posterior cochlear nuclei so this one right here is going to be the dorsal cochlear nuclei okay so we have two parts here once these fibers come in this cochlear branch of the vestibular cochlear nerve it fans out onto multiple cochlear nuclei within the actual pons medulla junction the the nuclei that are situated anterior are called the ventral cochlear nuclei the ones that are saturated post here called the dorsal cochlear nuclei now technically another thing happens we technically separate the ventral cochlear nuclei into two parts this is where it gets a little funkier so we separate these guys into two parts one part is going to be a little bit more posterior and one parts going to be a little bit more anterior so they call this one right here the ventral posterior cochlear nucleus and they call this one the anterior ventral cochlear nucleus all right so it's a little odd but yeah that's that's what they do okay so the ventral cochlear nuclei is actually split up into two parts the ventral posterior cochlear nucleus and the anterior ventral cochlear nucleus there's a reason why they actually kind of separate this for specific types of cells that make them up alright and we'll briefly mention that okay so now once these actual cochlear fibers boom synapse on these suckers right here a lot of different things are gonna happen so just stay with me okay let's start with the dorsal cochlear nucleus the dorsal cochlear nucleus has a bunch of different cells but the main ones here and the dorsal cochlear nucleus is going to be of two cell types one is they're going to be called principle cells and another one is you're gonna have what's called stellate cells okay what happens is the stellate cells and the principal cells give off their axons and these axons what they do is they start moving over moving over and they go to a special structure here located within the pons it's called the nucleus of the lateral luminousness we'll talk about that a second but if you look here the principal cells and the stylee cells they give off these axons okay and as these axons cross over to the other side they're also ascending at the same time we call this fibers or this tract if you will they called the dorsal acoustic striae okay so they call these fibers here the dorsal acoustic striae all right they cross over to the contralateral side and they pretty much synapse on a special special nucleus within the pons which is called the nucleus of the lateral M&S kiss so what is this nucleus here called it's called the nucleus of the lateral lemonis kiss okay then we go to this next one the ventral cochlear nuclei branch into two parts the ventral posterior and the anterior ventral cochlear nucleus the ventral posterior cochlear nucleus is mainly made up of cells I don't know why I laugh every time I think of these guys but they're made up of what's called octopus cells okay it's a real thing I know but they're called octopus cells okay so the octopus cells are going to be specifically situated in the ventral posterior cochlear nucleus what happens is these octopus cells give off their axons okay and these axons what they do is they do the same thing they cross over they don't ascend as fast but they cross over and then they actually move up so they cross over to the contralateral side and then they move up some of the fibers might actually synapse on the nucleus of the lateral meniscus some of them might not okay most of the fibers that sign apps on the nucleus of the lateral meniscus is the dorsal come sticks try but now these octopus cells they give off their axons from the ventral posterior cochlear nucleus the axons cross over to the contralateral side very little of them will synapse on the nucleus of the lateral meniscus most of them will continue to move upwards okay what is this structure here called well this is the dorsal acoustic striae this one on betch is gonna be the ventral acoustic stride they also called the trapezoid body so this one's got to be in between so they call this the intermediate acoustic striae okay so we have the intermediate acoustic strata which is formed by the axons of the octopus cells then we have another one the last one the Antero and taro ventral cochlear nucleus this one is gonna have a bunch of different types of cells here some of these cells here you're gonna have the actual jelly cells again so this is gonna have some of those stellate cells again and you're gonna have another one and these are called bushy cells and there's different types the main ones are gonna be what's called spherical and globular bushy cells okay now what happens here when these guys are stimulated they give their axons which also are gonna cross over to the contralateral side some of them here's what's different about this one when it crosses over most of the fibers here synapse on a specific point they synapse on these nuclei right here okay so they synapse on these nuclei right here some of them go to the contralateral side and some of them also go to the ipsilateral side okay when they do this okay what is this structure here first off formed by the axons of the spherical globular bushy cells and the stylee cells this one has two names you can call it the ventral acoustic striae or you can also sometimes you also hear it as what's called the trapezoid body okay sometimes you hear it as a trapezoid body now the ventral acoustic striae crosses over most of the fibers cross over to this green structure here within the actual lower pons some of them will stand the ipsilateral structure within the lower pons what is this structure here called this structure here is called the superior Oliveri nucleus so they call this the superior Oliveri nucleus this structure is super super cool all right there's two parts of it we'll discuss it in a second here okay but again these fibers some most of them will cross over to the contralateral superior very nucleus some of them will stay tipsy lateral when they cross over they call that the trapezoid body more specifically but again you can actually interchange that with the ventral acoustics try from here from the superior olivary nucleus these fibers can go up so now you're gonna have these fibers coming up here and moving with the dorsal acoustics try moving with the intermediate acoustic striae and what is gonna happen even some of the fibers from this what is this structure here so some of these fibers might actually continue here with the eventual acoustics try the dorsal acoustic striae what else are you gonna have you're gonna have the fibers from the nucleus of the laterally meniscus so it's nucleus and laterally meniscus some of these dorsal acoustics try fibers are going to synapse there then what happens they move up also look what you got here now so now you have the dorsal acoustics try the the actual ventral acoustics drive which synapse on the contralateral superior olive air nucleus and these intermediate acoustics trying as they're moving up some of them sign apps on the nucleus of the lateral luminousness the more prominent one though who does that is going to be this guy here the dorsal acoustic shrine some of the fibers might not sign up there though then you get this actual nucleus here he can give off axons that actually move upwards now as they're moving upwards they form attract if you will okay how would you define attract again attract is defined as a bundle of axons within the central nervous system well this tract is more flattened and so because of that it takes on a specific name which is lemonis guess they call it like I gotta have a flat tract what is this whole tract here call it's called be it's ironic the lateral lemonis 'kiss so this whole tract here this whole bundle right here is called the lateral lemonis kiss okay now as these guys go up there's some interesting things that can happen there can be some crosstalk there actually can be some crosstalk between the actual nucleus of the lateral meniscus from both sides that's really interesting because hearing is not just pure purely basically ipsilateral it's contrl are bilateral okay so if we actually have any damage to these structures here we still might be able to hear okay on both sides it just might be a little bit weak on one side why because the fibers coming from the other year also gonna cross so hearing is bilateral which is really really interesting okay so again nucleus at a lateral meniscus can have some crosstalk now where does this laterally meniscus structure go it primarily sign APS's on this structure located within the midbrain what is this structure located within the midbrain called okay this is a really important structure almost all of these fibers which usually should pretty much all sign apps on this structure they call this structure the inferior colliculus okay so they call the inferior colliculus so what is this purple nucleus here called they call this the inferior colliculus colliculus okay so now from here the inferior colliculus is really important cuz the inferior colliculus is actually there's another structure right above it called the superior colliculus you know whenever someone yells that you were safe sump says something you know sometimes you turn your head that way you you focus your gaze on whatever someone is where the voice came from that could happen the inferior colliculus actually controls a track that goes downwards a descending tract that goes to muscles that can move your head and your neck so where you can fix your gaze on wherever that auditory stimulus came from that's called the odd the actual auditory reflexes right so this can actually become a become a part of a tract that can go downwards and this tract that can actually go downwards we'll talk about this when we get to the descending tracts but this can actually form a track called the tech toe spinal tract and this plays a role with your auditory reflexes okay so if you hear something and you move your head that way or your neck muscles your head muscles fixing your eyes towards that point all of that is important with respect to this actual tech to a spinal tract now what's the more important thing for this guy though some of the fibers can go down to form descending motor tracks most of them though will go upwards as a part of this whole structure here and they call this structure the breaking of the inferior colliculus so most of the fibers will go upwards to a special nucleus around the thalamus and these are called the break IAM of the inferior colliculus okay so it forms this thing called the breaking of the inferior colliculus this is the brachial of inferior colliculus alright now once these fibers terminate on these nuclei what it what are these nuclei what are these baby blue nuclei here call these baby blue nuclei here that are situated on the thalamus are actually called the there's a specific body there okay easy way to remember this one is okay so it's actually kind of weird I like to do things a little bit differently put your eyes right there medial okay and your ears are lateral to you to your eyes so now with respect to that think opposite for the nucleus so my ears are lateral to my eyes so the nucleus right there has to be the medial geniculate nucleus okay so they call this structure here the medial geniculate nucleus of the thalamus because here's your thalamus there's a nuclei situated on it called the medial geniculate nucleus from here there's a radiations that will be sent out from this actual thalamus okay so now from here you're gonna have these actual auditory radiations that'll be sent to a specific part it'll get sent to a specific part of the actual temporal lobe so you know within the brain hey let me actually draw a small little diagram over here let me do this right here let's say here's the brain here right so now you know here's your temporal lobe right here's your temporal lobe right on the temporal lobe is an important gyrus okay right here is this gyrus this gyrus here is called the superior temporal gyrus okay another name for is they actually call this one the transverse gyrus of hashim it's a V call it the transverse gyrus of Hatcher oh the superior temporal gyrus now this area is important okay it's believed to be what's called the primary auditory cortex so they believe this area to be associated with the primary auditory cortex so it makes you aware of the actual sounds helps you to be able to perceive the sounds or that sound stimulus there's other areas around it which are like the actual us the auditory Association area which is important for being able to determine the meaning of the sound right you know this is another structure really important a little bit posterior to it so in order for us to be able to really comprehend the sound there's an area right here posterior to it yeah this area right here they call this Warnock's area so they call this Warnock's area so this area plays a role within the comprehension of speech so again what does this play a role within it plays a role within the comprehension of speech you know why that's important if someone's talking to you you're hearing them you're becoming aware of that sound that's the primary job of the primary auditory cortex right so you're becoming aware of the sound you're perceiving this sound stimulus you're relating it with different structures different nuclei within the brain to determine the meaning and the the actual does the the point of this sound stimulus then the wordix area is actually going to get some of those fibers some of that auditory stimulus to help us to comprehend the speech then what do you want to do you don't want to just sit there like a you know not responding to the person you want to be able to speak to them so you know what's really cool the Warnock's area talks to a specific area here located within the frontal lobe let's assume obviously this is the right part but assume that this is the left side because the Broca's area is only on the left side so right here in the frontal lobe there's another nucleus here and this is called the Broca's area he's the one that controls the muscles of speech okay so he controls specifically the muscles of speech so what happens is you get the sound stimulus goes to the primary auditory cortex you perceive the stimulus you also have the auditory Association area to help us to associate that sound stimulus with previous memories and help us to understand the importance of it then it can go to the wordix area so that we can comprehend the speech but then what if you want to talk back to the person let them know what that you understand it there's a fasciculus that connects the Warnock's area to the Broca's area they call this fasciculus the argue --it fasciculus it's called the arcuate fasciculus it connects to the Broca's area now what does the Broca's area gonna do the Broca's area has two telltale specific motor parts so you know there's motor Cortex's let's just assume that it's right here okay you have the primary motor cortex any of the premotor cortex let's just assume it's right there it's gonna tell that primary motor cortex the premotor cortex even the somatosensory cortex about that and then what is that going to do that's gonna send down these descending fibers where will these descending fibers go to they'll go to the muscles that control speech so that you can talk back to the person let them know that you comprehending the speech you understand what they're saying that's really important so with that being said what is this gyrus right here call again just a I'll make it playing the simple this is the primary auditory cortex which is within the temporal lobe and this is where the actual this part here is called the transverse gyrus of Heschel or the superior temporal gyrus so it's really important that we understand that so that we actually comprehend the actual speech okay because then there's a lot of other structures that will be associated with this now one more thing that's also important is that the inferior colliculus we didn't say this but you know the end fear colliculus it's also communicating with one another so there's crosstalk between the inferior colliculus there's crosstalk between the nucleus of the lateral meniscus as well sir so much crosstalk between these actual tracks just helping to influence the fact that the actual sound are hearing is bilateral okay making sure that we can hear from both ways now here's here's the important part I wanted to mention something about this nucleus here the superior Oliveri nucleus it's super super important really really important so we got to mention a couple things about this guy here so superior Oliveri nucleus I want you remember three basic functions of it okay three basic functions it's actually split into two parts a medial and a lateral we'll do it we'll do it real quick so we have a medial superior olive Airy nuclear complex right and then we have another one just a lateral superior Oliveri nuclear complex right the lateral one is specifically important with being able to play a role in the intensity of the sound okay so he plays a role in being able to determine the relative determine the relative intensity of the sound and I'm gonna explain what this means in a second of the sound stimulus right so he can determine the relative intensity of the sound stimulus the medial superior olive Airy nucleus here I'm not gonna be able to fit here let me put it below the medial superior olive airy nucleus he plays a role in determining the relative timing of the south so he helps to determine the relative timing of the sound stimulus okay so now let me explain this because there's one more function I want to mention for this guy so again here the lateral superior Oliveri nucleus and the middle super medial superior olive a nucleus lateral plays role within the intensity of the sound if you had to remember at least one word from these guys at least remember intensity and the middle medial superior olive area nucleus plays a role within the relative timing of the sound stimulus now how can I explain this okay so the superior very nucleus let's say that I'm talking to you right and I'm talking straight in front of you or I could be talking behind you or for whatever weird reason I'm above you and I'm talking above you if I'm talking in front of you behind you or directly above you the sound waves will get funneled into both ears at approximately the same time so the reach the superior very nucleus of both sides at about the same time but then let's pretend you're standing right here okay and I'm talking into your right ear the sound stimulus will reach the right superior very nucleus first and then it'd take a little bit of time but it'll reach the left side left ear then the lefse parallel very nucleus so he plays a role being able to determine where the actual sound is coming from he helps us to play a role big big point here just a big overall picture if you don't even remember this at least rumor at this point he plays a role in being able to play a role on place a role and localization localization of the sound okay so he helps us to localize the sound where the sound came from is it behind us in front of us side of us where is it so he is really really important for that one more thing he's important for if we talked about this when we talk about the cochlea but if there's really loud sounds really really loud sounds that could be possibly damaging to your actual hair cells this guy he's pretty nice to us and what he does is he has some fibers and these fibers he activates this dis bundle there's a bundle it's called the olivocochlear bundle so from this super alberry nucleus he helps to form this structure here called a olivocochlear bundle and what this olivocochlear bundle is is it's actually going to be cholinergic neurons which means it releases acetylcholine these neurons are going to come over here to the cochlea so now let's go over here to this cochlea for a second and now what I'm gonna do is is I'm going to have these fibers in turn aiding these structures particularly though more of the fibers are going to go to these hair cells what do we say these hair cells were we called these hair cells since they were outer we call them the outer hair cells so primarily most of these efferent neurons are going to be going to the outer hair cells if you remember why that's important remember those those molecules called Preston it releases acetylcholine which hyperpolarizes the outer hair cells the Preston molecules will no longer do what they're no longer going to contract if the Preston molecules don't contract the hair cell doesn't shorten anymore it actually along gates what does that do to the bacilli membrane it bows the vasila membrane downward if it bows the pasilla membrane downward is that going to cause a lot of shearing of the actual hair cells the stereocilia no if the stereocilia aren't beating towards the kind of psyllium is there gonna be a lot of activation no and so what is that going to do the action potentials that are being sent down this neuron it's gonna decrease it so it's a way of being able to protect our hair cells there's another way though - one more area this guy is always pretty important because you know whenever you're there's a really really loud sound you're becoming very alert of it there could be a lot of sounds going on in the room but if there's someone that just speaks out really loud and just scream something for whatever reason there's a special nucleus a special sheet of gray matter which is kind of located around all the way front parts the midbrain the pons and the medulla this guy is called the reticular formation so whenever there's really really loud sounds high amplitude sounds the reticular formation will alert our central nervous system or entire cerebral cortex they become us make us alert aware of the sound stimulus some of the information can even go to the parts of the cerebellum - okay so now this reticular formation he's not only going to be important for being able to aware us of the actual sound stimulus that loud amplitude loud high amplitude stimulus he's also going to activate two different nuclei okay one right here and then one right around here okay so what are these nuclei let's say that I have this nucleus right here and this one is really important he's going to bring these impulses to a specific part of the actual middle ear you know there's a muscle right around this area actually hold on we'll talk about that in just one second let me bring the other one over here to there's another muscle another nerve that's also going to be stimulated this red marker socks let make another one all right they had this guy right here you're going to activate another nucleus which can also move out here and innervate another muscle so there's two muscles and that we're gonna innervate this blue neuron this blue neuron we're gonna call this guy a specific type of cranial nerve this is actually cranial nerve five the trigeminal nerve okay we have another nerve which is running right next to it here to this area to the middle ear and this structure is going to be cranial nerve seven the facial nerve these are gonna go to special muscles in this area so now this cranial nerve creating our five go is the trigeminal nerve right he's gonna go to a special muscle this special muscle that he's going to go to around the middle ear is gonna be called the tensor tympani all right now let me explain how this works let me say here I have malleus all right so here's malleus okay now malleus is actually connected to the tympanic membrane all right so he's connected to the tympanic membrane so let's say here we have the tympanic membrane like this right well there's the little part here the medial part of the malleus what happens is there's a muscle called the tensor tympani and this muscle works we're gonna draw them blue here to color coordinate is gonna be called the tensor tympani okay it's right around where the eustachian tube is where he actually going to be connecting now what he does is is when the actual crane and their five comes over here and innervates it stimulates this muscle he's going to contract and when he contracts he pulls on the malleus when he pulls on the mouth guess what he does to the tympanic membrane tightens the tympanic membrane thus the name tensor tympani it tightens or tenses the tympanic membrane now the tympanic membrane isn't going to be as sensitive to that sound waves so it helping to dampen the actual sound waves so it helps to dampen the sound stimulus and that is just so darn cool so another way of our body being able to protect us from certain situations which could damage our hair cells okay is by activating this muscle right here and again what is this muscle here called this muscle is called the tensor tympani now what about this other one what about this other muscle the other muscle is gonna go to from this actual facial nerve is called the who this markers good stapedius so it's gonna go to a muscle called the stapedius now the stapedius is a pretty cool muscle and what it does is it actually connects to yeah you guessed it the actual state bees okay now what happens this is you know stay piece is responsible for being able to tap onto the oval window creating fluid-filled vibrations and whenever there's loud sounds it's gonna tap really really hard and really fast what we can do is is we can have this stapedius muscle become stimulated by the facial nerve and what's it gonna do it's gonna pull on the stapedius and it's gonna prevent the stapedius from tapping on the oval window if it pulls the stapedius the actual Stevie's will tap on the oval window as much and as hard it's not gonna create as much fluid fel vibrations which is gonna prevent less hair cells from being activated again another way of being able to dampen the sound stimulus to prevent damage to our inner hair cells so I think that's a beautiful beautiful thing okay the last thing I want to talk about because it's relative it happens in some people and it's an unfortunate thing there's a pathology called an acoustic schwannoma they call it acoustic Schwann oma now this is actually it's not it's not too common it can happen though and usually the only way to be able to see this is sometimes you'll see um the person can exhibit like vertigo they can have tinnitus which is basically like the ringing of the ears they might even have other types of problems where they actually have might even have a loss of hearing okay so an acoustic schwannoma what's what's actually the cause of this what's the cause of an acoustic chuan oh okay so let's actually say here very very briefly let's say we have a cell alright and the cell you know you had your cell has specific types of you know genes right that's occupied within the nucleus right here's your DNA there's specific genes that are regulating specific types of protein synthesis let's say here's this gene right here this gene right here is called neurofibromatosis type 2 gene right what it does is is it produces a special type of protein and this protein that we're making actually gets secreted out of the cell right it gets secreted but what it does is it binds on to an actual protein here on the cell membrane there's a protein here in the cell membrane this protein that's it's it's called cd44 right what happens is this neurofibromatosis type 2 gene produces a protein called Merlin and this Merlin binds on to the cd4 T for protein okay what is this protein here called it's called Merlin this Merlin protein binds on to the cd44 and what that does is it allows for this Merlin protein the cd44 and you know cd44 TS can actually actually connect it to some actin molecules inside of the cell what this does is once you have this whole complex here so for example let's say that here's the Merlin protein and then right connected to it is actually going to be cd44 protein which is a part of the cell membrane and then connected to that is going to be the actin molecules right and the actin molecules are helping it to be able to support the cytoskeleton so now here's the cell membrane this part that I'm drawing here what's important is that this Merlin in cd44 is actually connecting to the extracellular matrix why is that important in a situation which someone has an acoustic schwannoma guess what they don't make they don't make actually this Merlin protein because there's some type of damage to the neurofibromatosis type 2 gene if they don't make the Merlin protein it can't connect to cd44 if cd44 Merlin are not connected that means that the cell isn't actually connected to the extracellular matrix what can I do then it can start dividing and then it starts dividing and dividing and dividing guess what it starts making it starts making a huge mass and usually this mass occurs in like around the internal acoustic meatus and actually kind of around the cerebellopontine angle and what it does is actually can compress the nerve fibers and obviously this can lead to hearing loss it can lead to tinnitus the ringing of the ears depending upon how big it is it can actually affect our balance too because it might affect over a tubular system ok in this last situation here is you know these actual little obstacles these little bones here sometimes due to frequent infection or if as you just get older he starts actually developing a lot of fibrosis and it causes these actual ossicles to become thickened and hard and not able to move as much when during the response to the sound waves and that can actually cause a specific type of deafness so what does these actual guys do this is this actually happens due to otosclerosis otosclerosis is actually going to produce deafness it can't produce deafness but this is called conductive deafness ok other types of conductive deafness is if you have ear wax that's really really building up within the external acoustic meatus that can also affect the actual sound waves but the acoustic schwannoma this is actually due to effect of the actual inner ear structure so this is actually called a sensory neural deafness okay ein engineer so in this video we talked about the auditory pathway specifically following the cochlear branch of the vestibulocochlear nerve guys I really hope it made sense I hope you guys did enjoy it if you guys did learn a lot if you guys if it did make sense please hit that like button comment down in the comment section and please subscribe guys alright also if you guys want please go check out our Facebook our Instagram and even our patreon if you guys have the opportunity to donate we would so appreciate it alright and in tears as always until next time [Music] you [Music]

Channel: Ninja Nerd

Views: 354,683

Keywords: neurology, vestibulocochlear nerve, cranial nerve VIII, auditory pathway

Id: V8AZ6QygeYs

Length: 43min 36sec (2616 seconds)

Published: Thu Jan 04 2018