I ninja nerds in this video we are going to talk about the dorsal column medial lemniscus pathway this fatha is super super important because it controls a lot of our touch or proprioception pressure vibration stretch so we're going to go into this pathway in great detail so let's go ahead and get started so if we come over here we're gonna talk first off again what are we gonna talk about the main topic here is the dorsal column medial lemon Niska pathway okay so that's what we're gonna talk about in this video that's one heck of a name now the dorsal column medial meniscal pathway we said that it is going to be important for carrying what types of sensations okay so the dorsal column medial meniscal pathway is important for being able to pick what's called pickup discriminative discriminative touch so fine and discriminative touch what does that mean sometimes you might even hear it as what's called two-point touch this is this is really important so two-point touch are finding the discriminative touch imagine me taking my fingers and me poking different parts of my hand my eyes are closed let's say that I closed my eyes either it could be my eyes closed my eyes open and I'm touching my hand at two points and I can tell that there is two points of contact that is what this system is really good at so finally discriminative touch and we'll talk about what type of receptors pick that up another thing it's really good at is what's called picking up pressure and stretch I like the skin so we'll be able to pick up pressure placed on the skin stretch of the skin and another thing that it can pick up is vibrations and even vibrations okay there's some special receptors we'll talk about with this but really really really important one is what's called proprioception so another one that is extremely crucial here is called proprioception so we have to define what proprioception is so proprioception is basically knowing one's position of their joints their ligaments their muscles in space so beat me being able to know that my arm is over here my finger is on my nose is now on my eye it's on my chin I'm actually aware of that even though my eyes are closed I'm consciously aware of where my hands are right now that is what proprioception is it's really important because our cerebellum and our central nervous system cerebral cortex has to be aware of these types of situations remember that now one more thing this dorsal column medially meniscal pathway is what's called an ascending tract okay this is specifically it's an ascending tract because we're talking about ascending tracks now how would you talk how would you define a tract this is really important a tract is a bundle of axons in the central nervous system okay so a tract is a bundle of axons in the central nervous system ascending means it's going up so let me say here I draw cross section or another cross section a sagittal section of the central nervous system right here spinal cord medulla pons midbrain and then a cerebrum right if we talk about a tract a tract is going to be this let's say that here's this you know this axon here that's coming out with this like peripheral process picking up some type of stimulus so there's a stimulus out here right here's the stimulus and the stimulus is going to activate some receptor the receptor is connected to some type of cell body we'll talk about this that gets projected into the actual spinal cord and then goes up and it goes up to specific parts of the central nervous system well you have many of these that are collectively so imagine here let's pretend that this is at the lumbar region let's pretend that this is at the thoracic region this can get added on let's pretend that this one is here at the cervical region this one can get all added on so this bundle of axons here running through the central nervous system is what's called a tract and because it's going up to the central nervous system it's referred to as a ascending tract there's many of these we're going to talk about the dorsal column medial luminous Co pathway will talk about the anterolateral system or the spinothalamic tract and we'll talk about the spinocerebellar tract and some other accessory ones but just remember what is a tract it's a bundle of axons in the CNS that's super-important now let's go ahead and talk about so we know what this dorsal column is specifically responding to the types of stimuli but now we have to understand how do we pick up that stimulus alright so let's go ahead and talk about that so let's come over here so we know that the dorsal column is specifically responding to discriminate a touch okay how does it do that there's special receptors so you know there's receptors if you imagine here pretend I take like a very crude diagram of the skin all right here's your epidermis you know the epidermis you have these little peg like projections right here there's special receptors in here called meissner's corpuscles and these guys are actually going to be right here in the dermal papilla and they pick up very fine and discriminative touch so what could you have over here let's pretend that this is actually the guy here it is boom there is our meissner's corpuscles all right so first one here is going to be your meissner's corpuscle okay what else another one that's really important is it's actually kind of situated you know there's different stratum of the epidermis like the stratum corneum stratum lucidum shine of granny low some shadows spinosum and then a last one which is right here on this edge right above the dermal papilla is the stratum Bissau the stratum Bissau has specific types of receptors here that pick up very fine touch and very superficial pressure what are these guys called they're called Merkel's disks so you're also gonna have some other structures here and these are going to be called your Merkel's discs they responds a very very fine touch and also superficial pressure all right what else do we have we have other ones here too that are actually a little bit deeper there can be found like the dermis the hypodermis you can find them in your interosseous membrane you can even find them in the parrots like in the actual mucous membranes of your GI urine or genital tract they'd be fun in many different places and these are called your prosimian corpuscles or your lam elated corpuscles okay so what's another one here that we can have we could also have the pacinian corpuscles so we can have what's called pacinian corpuscles wow there's so many of these darn things so you have Mart meissner's corpuscles pacinian corpuscles Merkel's disks what else do we have I'm glad you asked let's pretend here is actually going to be a hair follicle right so here's your hair follicle around that hair follicle to be able to pick up the bending and the movement of the hairs you have special types of nerve fibers they're right here around it picking up different movements in the hair that is gonna be called the pair each Rykiel nerve endings so what else do you have here you also have what's called the peri try keel nerve endings so many darn things okay another one and this responds specifically to like the stretch of the skin okay so it's responding to the stretch of the skin and vibrations let's do this one in this orange color oh yeah let's do this one so this last one here it can be found in the the dermis it can be fun in the hypodermis you can find it even in your joint capsules and it's responding a lot to stretch of the skin and even vibration senses so these are called your roof innie corpuscles sometimes they even call them bulbous corpuscles okay so you have your roof any corpuscles which respond to the actual specifically vibrations and stretch of the skin peri tracheal nerve endings which are responding to the bending of the hair and a little bit of touch pacinian corpuscle to responding to deep pressure right and Merkel's discs which are responding to very fine touch and superficial pressure and then meissner's corpuscles which are actually gonna be responding to find the discriminative touch okay the pacinian corpuscle is they respond a little bit more to vibrations than roof any does roof inning is mainly for stretch okay but pacinian it can respond to a little bit of vibrations but pacinian is mainly for the actual vibrations okay so we got all these that's for the discriminative touch that's for the pressure that's for the actual stretch and the vibrations now we have one more that we have to pick up that's proprioception this pathway is so unbelievable it really is so there's another one in our muscles you have we'll talk about it's more in other videos maybe but when we talk about the muscles right our skeletal muscles we can break it down into two different components right so you have what's called extra fusil and then you have what's called intrafusal okay muscle fibers I'll put intrafusal fibers though so you have intrafusal fibers and extra fuses fibers the extra fuse the ones are the main ones that are contracting they're pretty much the bulk of the muscle the intrafusal fibers have different types of they're basically being able to detect stretch okay there's actually two types here okay one is called nuclear chain fibers and the other one is called nuclear bag fibers and what these do is is they respond to stretching of the muscle so whenever the muscle is stretched it can activate these nuclear chain fibers and nuclear bag fibers if you really want to be specific nuclear chain response to the perpetual onset of the stretch of the muscle nuclear backs responds to the progression the progressive stretch of the muscle now these guys are picking up stretch all right of the muscles so let's actually represent these guys coming from here and what are these guys here these ones are going to be the proprioceptive fibers which are coming from the nuclear chain and the nuclear bag fibers okay so that's going to be important so these are going to be coming from the we also give them another name we also call them muscle spindles but they have a name for this fiber type they call this type 1a fibers okay so they call them type 1a fibers okay these are coming from your actual nuclear chain and nuclear bag fibers now there's another thing you know there's tendons right tendons are connecting the muscles to the bone well in the tendon you have a receptor that picks up the stretching of the tendon so whenever your muscles are contracting let's pretend for whatever reason I'm trying to curl some extremely heavy weight right so I'm getting my gains on and I'm just I'm yeah you know I mean so I'm trying to lift it and I'm stretching the muscle right but as I'm doing that let's say that the tendon the weight is just way way way too heavy and it's really pulling and pulling on the tendon to the point to where it's getting ready to evolve from the bone we have a protective response for the most part obviously that can tell our body hey this is too much stretching on the tendon that it's gonna evolve pretty soon we need to protect that from happening so there's special receptors located in that tendon that respond to the stretch of the tendon and these guys these receptors here called your Golgi tendon organs are gonna put GTO here okay Golgi tendon organs they respond to the stretch of the tendon and they're being carried down through what's called 1b fibers okay and all of this information look how much information is coming in here we're gonna have information coming from the meissner's corpuscle x' coming from the Merkel's disks the pacinian corpuscles here so many of these structures here so what else do we have we have the pacinian corpuscles we have the peri tracheal nerve endings we even have the Ruffini corpuscles all this stuff is going to be going into the central nervous system it's unbelievable what else Ruffini corpuscles okay guys so I just brought all these guys together because all of these fibers are gonna be going into the actual spinal cord now before we do that right so we know what the dorsal column is are responding to what stimuli we know the receptors that are picking up those stimuli again these guys being the appropriate receptive aspect but now I need to talk about one type of thing here this pathway this dorsal column media in the Luminess school pathway is extremely fast it's an extremely fast pathway and there's a reason why remember we talked about this a couple times before but there's different types of nerve fibers okay different types of nerve fibers there is what is called a B and C nerve fibers only thing that differentiates them is their degree of myelination a being the most myelinated all the way till C being the least myelinated where B is actually going to be moderately mounted C is actually pretty much sometimes we even say it's not myelinated this being the slowest conducting fibers medium conducting fibers and the fastest conducting fibers but here's the thing a can actually branch out into a couple different types there's a alpha there's a beta and there's a delta delta is more for the fast pain the prick pain right and even for some crude touch and pressure a alpha is for the muscle spindles in the Golgi tendon organs so this is specifically going to be for the muscle spindles and for the Golgi tendon organs the a beta is for all of these the meissner's corpuscles the Merkel's disks the pacinian corpuscles the pair tracheal nerve endings Ruffini corpuscles now what's the difference the Alpha is the fastest so the fastest one is going to be the a alpha this thing can travel up to about 120 meters per second that's insane this one being the slowest of these a fibers okay traveling up to about 30 meters per second the a beta is right in between right so a beta is for more of these actual pressure touch vibration and discriminate a touch sensations all right now now that we've done them we have to take these fibers into the spinal cord right so we've made cross sections of the spinal cord here so if we take these cross sections there's two cross sections here one over here this is going to be for the sake of simplicity we're going to make this the cervical part of the spinal cord and we're gonna make this one over here the lumbar part of the spinal cord okay now watch what happens here when we talk about this actually you know we're going to do make it even easier we're gonna kind of add on to this cervical we're gonna actually kind of refer to this because there's an important functional aspect here we're gonna say above t6 and we're gonna refer to this as below t6 and there's a reason why I'm talking about that sixth part and the reason why is we're gonna talk about two different types of fascicular all right trust me for right now we'll cut we'll cover it so now what I'm gonna do is I'm going to take all these fibers here we're gonna bundle them together and these fibers here are gonna be coming in to this first order neuron and whereas this force first order neuron located remember it's located in what's called the dorsal root ganglion all right which is in the posterior root right of the dorsal root and a gang now what's a ganglion a gang that is a group of cell bodies located within the peripheral nervous system so this is our dorsal root ganglion with our pseudo unipolar neuron there he has his central processes projecting into the posterior or dorsal gray horn from here these fibers will then funnel in without synaptic into this part right here you see how we have this little separation here this dorsal median sulcus here we have this little dorsal median sulcus or fissure here in the posterior aspect and closest to that fissure is going to be this fasciculus that we're going to talk about which is going to be developing below t6 this one right here this fasciculus that we're gonna talk about is called the fasciculus gracilis we'll talk about this more we're gonna just bring this guy up for right now though so we're gonna bring him up and here he is coming up this way alright so here's why fasciculus gracilis so the fasciculus gracilis is picking up information from below t6 so it's picking up from the limbs the legs the lower body trunk okay so what is this structure right here called this one is called the fasciculus gracilis and again the fasciculus gracilis is taking information from the lower limbs and the lower body trunk or specifically we can say from below t6 now at the same time we're going to have let's bring different color just for the sake of making it look pretty here let's say that these fibers these Merkel's disk meissner's corpuscle is percenter and corpuscles pair tracheal nerve endings or Finny corpuscles muscle spindles Golgi tendon organs all this stuff is coming out of the cervical level or above t6 when that happens the information is going to get funded into the dorsal gray horn and again what is this part here guys don't forget this is the dorsal root ganglion from here the central processes are going to project in to the dorsal white column you know the dorsal white column is all this part here this is the lateral white column and this is the ventral or the anterior white column so what it's going to do is it's gonna funnel in though lateral to this it's gonna funnel in lateral to this so this structure right here which is finally in lateral is gonna be a different type of fasciculus this fasciculus is called the fasciculus Tunney ADIS now here's how I like to remember it the gracilis muscle is in your leg right so fasciculus chrysalis is picking up information from the lower limbs it's an easy way to remember if you want fasciculus Junius as due to that left over you can say okay that's going to be coming from the upper limbs in the upper body trunk so now fasciculus cuny ATIS fasciculus gracilis these are going to be coming up to the spinal cord right specifically within the dorsal column now there's one more thing that I have to talk about because there's what's called a somatic topic arrangement here if you notice something let's actually come over to this diagram here let's modify this one a little bit though we're gonna modify this diagram a little bit to explain the somatic topic organization so let's say here I draw another section here okay now let's say first we come from the lumbar right here's the lumbar region these fibers are gonna come in towards the midline okay so they're gonna come in towards that midline portion and then go up then over here you'll have thoracic these are gonna gonna come towards the midline region and go up and then you're gonna have cervical and that's gonna come towards the midline region go up and if you want you can even say sacral that's gonna be all the way here why am I telling you this there's a way of being able to determine how this information is going up through the dorsal luminousness so the dorsal column sorry what would be right here what would be towards the medial aspect the most lower aspect of the limb so what would you have here towards the medial this would be where the sacral region is so the fibers coming from the sacral part let spinal cord what will be next to it there be lumbar so lumbar is gonna be a little bit more lateral what's going to be even more lateral to that the thoracic what's gonna even be more lateral to that the cervical so the somatic topic arrangement here is really truly important you have to remember that that feeding in here most medial is the lower limbs and as you go up they just keep feeding in lateral to that why is that important if there's a lesion right here it can affect the sacral and lumbar region but not the thoracic in the cervical region or if there's a lesion more outside more laterally you can affect the cervical and thoracic and not the lumbar in the sacral that's why it's so important to understand the somatic to a bigger region one more thing that's important if you notice when these fibers are going into the actual spinal cord do they cross do they go to the contralateral side no they go to the ape see lateral so they stay on the same side of the spinal cord so if we kind of make a section right here down the middle this side that side they stay on the ipsilateral or the same side that's really important so this pathway is if see lateral at level of spinal cord okay that is super super important and it's important for clinical situations okay so now we have the figure fasciculus cuny Attis we have the fasciculus gracilis so we know our first order neuron first-order neuron was this point right here where the dorsal root ganglion is okay so this is our first-order neuron so or order this our first-order neuron now how does this work the first-order learn if you remember this was the cell body right the pseudo unipolar neuron it has peripheral process going out to where the receptor is picking up the sensation central process is going into the spinal cord and this is the axons of the first order neuron going up either as the vesicular sillas below t6 fasciculus cuny ATIS above t6 now where do these guys go they go to a second order neuron and these second order neurons are located within the medulla kind of in the posterior part of the medulla these guys here are actually going to be a group of cell bodies within the CNS that's why they call my nucleus now this one right here is the nucleus gracilis and again over here on the right side is the nucleus gracilis over here this would be the nucleus cuny ADIS and over here this would be the nucleus can itís so fasciculus cuny ADIS is gonna go where soon the go here and then what would you have over here you'd have the fasciculus chrysalis sign app seing where on the nucleus gracilis and again on the same side now really fast here we go dorsal root ganglia on here feeding in going up this is going to be coming up here more medial and where is this fasciculus gracilis here gonna go it's gonna go to the nucleus gracilis right same thing from the upper parts are above t6 what are you gonna have you're gonna have the dorsal root ganglion coming in here funneling in where it's gonna be funding in funneling in a little bit more lateral moving up as the fasciculus CUNY ATIS okay so what do we have here collectively guys we have the fasciculus CUNY it's which are the ones that are in red and this is going to be the right fasciculus CUNY ADIS this is the left fasciculus CUNY Attis then what are these blue guys here called these blue guys here are going to be called D fasciculus gracilis this is the right side and this is the left fasciculus gracilis okay now as these guys sign apps here on their second order neurons so what are these guys here these are the second order neurons and again where are they located at what part of the brain stem this is the medulla oblongata right and this is the pons and then midbrain here and then you have your cerebral cortex out there right now from here something really interesting happens remember I told you there was a PC lateral the entry of the spinal cord and as it's going up guess what it changes now as we get up here to the nucleus CUNY ATIS and the nucleus chrysalis these guys formed little connections and what they do is is they cross over to the opposite side so they kind of form like these little arc alright so look at this the same thing here same thing here they're gonna kind of cross over here to the opposite side what is this part here called where they cross and they go to the contralateral side what are these called a little crossing part they're that crossing part there is called the internal arcuate fiber so this is what called the internal arcuate fibers there's a reason why they call it internal because there is an external net specifically for the kunio cerebellar tract and we'll talk about that now they cross over now if they cross over they cross on the dorsal part of the pons behind actually I'm sorry they cross and the dorsal part of the medulla just behind the pyramids right and they move up through the medulla through the pons through the midbrain as a special structure after they cross what is this structure here called this bundle here well it's called the medial lemniscus and guess what this is the left one so what would this one be over here this would be the right one so this one over here is going to be the right medial lemniscus and this is going to move up through the brainstem as it moves up through the brainstem it's going to converge on a specific nuclei located within the thalamus okay so this is going to move upwards here as the medial lemniscus and it's gonna sign apps on a special nucleus located in the thalamus what is this special nucleus here called this nucleus is actually going to be called the ventral posterior lateral nucleus same thing over here ventral posterior lateral nucleus there's another one called the ventral posterior medial but that's gonna be picking up there's actually another track that kind of kind of comes right with the medial lemniscus it's called the trigeminal thalmic tract it kind of comes up words but it goes - it's called the ventral posterior medial nucleus we're not going to talk about that but these medial lemniscus structures they come upwards and they sign apps on these these third order neurons because we're a third we hit second which was the nucleus gracilis and cuneus we hit first which was the dorsal root ganglia this is the next guy so this is our third order neuron so this is our third order neuron which is in the thalamus is the ventral posterior lateral nucleus of the thalamus from here these fibers go to a specific part they go here you know this is the internal capsule right here and the internal capsule has like a posterior limb and it has like this portion here called the G new and then as the anterior limb and then you have another structure if you want to know your neuroanatomy you know that you have what's called the linty form nucleus over here which has the put'em in and then a Globus Politis internist externa s-- and we even have an external capsule and then the I was called the colostrum right outside of that what's really important here is this part here you know we have the post here limb the posterior one-third right here of the internal capsule is where this nuclear the ventral posterolateral nucleus has its axons move up through this the posterior limb with the internal capsule now you're probably wondering why is why is it that important to remember this there's a reason why it's important remember this there's arteries that supply this structure here the internal capsule and if at any situation there is an infarct in these arteries you know there's what's called the lenticular striated arteries which are branches of the middle cerebral artery the lenticular Striders if there's some type of infarction it can affect the internal capsule and that would affect the fibers that are going up through there the sensory fibers so you might lose sensations right and that could be very very bad so again what's gonna happen here I'm at your posterior lateral nucleus moves up through the posterior limb again what is this here posterior one-third limb of internal capsule which is a projection fiber and then it comes up through look what's called the corona radiata and that is a radiating crown that's going to different parts of the cerebral cortex but it's going to specifically one really important area are two about 2.4 daenerys you know um look we have this diagram here let's pretend for a second I've make this the central sulcus right here there's a special gyrus which is located just posterior to the central sulcus it's called the post central gyrus also called the primary somatosensory cortex there's another small one right behind it which is called the secondary somatosensory cortex we also kind of refer to this as since this is primary somatosensory cortex we call it s1 and since this is the secondary somatosensory cortex we call it s2 it's mainly going to these areas well there's an importance to this so again it's going mainly to these areas out here now let's assume that this is the primary somatosensory cortex and the secondary somatosensory cortex same thing over here that troposphere lateral nucleus goes to the internal capsule posterior limb of it post your one third and this gets sent out through corona radiata to different parts of the cerebral cortex there's an important thing for this we need to talk about this let me come over here real quick let me draw a small little diagram it doesn't have to be anything important but I just want us to get this part here so what I'm doing here is I'm just drawing kind of a small section here of the actual parietal lobe okay small section nothing crazy here let's just imagine there's a small section of the parietal lobe our parietal lobe is arranged in such a way in such a way that certain sensations go to specific areas of the actual primary and secondary somatosensory cortex primarily the primary though and how does it work for example let's say here right here right where we're talking about that where the central sulcus is or you have at this point right here let's say this is a longitudinal fissure right here you have what's called your external genitalia any sensations from the external genital genitalia since right here at that port right there in that point right there if we go up maybe we have the foot the foot can be fell at that point right there go up even more maybe the leg then the hip then the trunk of the body then maybe the neck then as you keep going maybe you actually have what else you have the arm you have the hand and the thumb and as you keep going you have your face you might even have the tongue the pharynx and even intra-abdominal there's a specific somatic topi okay so this is the somato topic organization sometimes you might see this in textbooks as like a little man you know little man is actually referred to as a homunculus so this is our sensory homunculus so when information is going up imagine right here is the where the thalamus is right here imagine right here's what the thalamus is okay from here any fibers that are coming up and going to specific parts of the cerebral cortex are going to a specific area that is associated with sensations to that specific location of the body so if someone kicks in the nuts it's going to be going right here to this part of the primary somatosensory cortex if someone steps in your foot it will go here you get the point that there's a somatic topic organization of the actual post central gyrus alright so we covered this in pretty good detail now one last thing I wanted to talk about this internal capsule you know it's a specific type of fibers this this internal capsule is actually referred to as what's called a projection fiber okay and projection fibers are important because they allow for information to kind of go up and down so that's what's our really important this internal capsule and another structure called the corona radiata our projection fibers their bundle of white matter so in a way they're kind of like a tract but they're different again they're actually going to be taking this information upwards and they can take information downwards via through motor pathways the corticospinal tracts which we'll talk about in another video that's really important last thing is you also have other structures here like Commission and Commission fibers are important like for example the corpus callosum they allow for information to go from right cerebral hemisphere to left cerebral hemisphere right and that's an example of the corpus callosum another one is called Association fibers and Association fibers are important because they allow for information to go front so let's say anterior it's a posterior right or posterior to anterior Way and these are like an example of this one is like the arcuate fasciculus which connects the Warnock's to the Broca's so there's different types of structures different white matter fibers which are going to be in the central nervous system that are super super important and I just want I thought I'd take a little bit of time to mention that real quick alright engineers so I hope all of this made sense I really hope that you guys did enjoy it if you guys did like the video please hit that like button comment down the comments section and please subscribe also check out our Facebook Instagram and even our patreon account if you guys have the ability to donate we truly appreciate it alright engineers as always until next time you [Music] you [Music]