for whatever reason lecturers come in neurologists come in sometimes they're not even neurologists that teach this subject honestly which is a huge disservice but anyway these these people come in and they spend so much time talking about the connections and the synapses and what neuron projects to where and which is contralateral and ipsilateral and it just gets so overwhelming and they miss the point so I'm gonna start with a lot of background as far as what I think you should know for boards this will not be all-inclusive I'm not gonna touch on the nitty-gritty of every single pathway no no I'm gonna talk about the high yo facts what each of these pathways do and how they are manifested clinically and how they can be tested on boards so with that said we're gonna focus on three spinal cord pathways the posterior column which controls discriminative touch or fine touch and proprioception the corticospinal tract which is really our upper motor neurons so these are the motor neurons that descend from the motor cortex in the brain and control our movement and allow us to kind of fine tune movement and then we're gonna finish up with this lateral spinothalamic tract which is responsible for temperature and pain sensation at the very end of the video we'll talk about something called Browns two-card syndrome which is a really high yield topic that they love to go after on boards and it you have to understand how these spinal cord pathways work in order to get the question right and understand Browns two-card syndrome so this is usually what people see in first aid they see this crazy-looking slice of a spinal cord with all these different tracts they start to get nauseous because they have to know what tract goes away or what controls well at which side it's on is upper nor on is it lower motor neuron is it you know sensory whatever it sucks guys so let's just take a step back and kind of dive into each of these tracts individually and we'll get through this really quickly and in a high yield fashion so we're gonna start with the posterior columns and the posterior column pathway looks like this and don't freak out because it's really not that bad we're gonna go through this so first what does the posterior column spinal tract pathway do well it controls your fine touch and proprioception and they have a descriptive term for this and it is discriminative touch so discriminative touch is our fine touch and proprioception in this pathway there are three synapse and the synapses you can see in the diagram on the right side of this slide but I'm gonna list them for you the sensory neurons you know somewhere in like your fingertips are in your toes wherever it is will sense the signal and send the signal up to the dorsal column nuclei and you see that here in the slice of the medulla in the center of the picture the first synapse occurs between the sensory neuron that projects up and goes to the dorsal column nuclei that dorsal column nuclei will decussate at the medial lemniscus and then project upward to the thalamus remember that the thalamus is sort of our sensory integration center of the brain so it makes sense that sensory signals are being inputted from the periphery up and they make their way to the thalamus once at the thalamus we send that neuron the third and final synapse to the primary sensory cortex which is the cortical center of the brain responsible for processing all incoming sensory information so in review so far posterior columns do discriminative touch there are three synapses sensory neuron to dorsal column dorsal column to thalamus and thalamus to primary sensory cortex not too bad right well how do we remember this because isn't that what this channel is about giving you guys a mnemonic to understand this you know physiologically but then take that a step further and be able to instantly get the point right on us Emily or comlex so the posterior columns are the PC PC for politically correct so posterior columns PC PC is politically correct and remember our synapses are sensory neuron two dorsal column two thalamus two primary sensory cortex so s D T P and if you are politically correct we want to say that mnemonic is some doctors think politically SD T P some doctors think politically so posterior columns PC politically correct some doctors think politically s for sensory D for dorsal T four thalamus P for primary sensory cortex so that is our posterior columns some doctors think politically and this makes sense right the problem that you'll have if your posterior column does not work is that you'll have problems with discrete nation right and if you're politically correct you don't discriminate so isn't that beautiful how the mnemonic ties into exactly what the posterior column does if you have a problem with your posterior columns you're gonna have problems with discrimination and remember that our posterior columns our PC are politically correct our posterior columns are responsible for discriminative touch and that's why problems with discrimination if you don't think politically if you don't SD T P if your posterior columns do not work so that's supposed to your column we're already done one of the three major spinal spinal tracts that you need to know moving on we're gonna talk about the corticospinal tract so the corticospinal tract is basically our upper motor neuron right it is the control that descends down from the primary motor cortex makes its way all the way to our muscles in the periphery and controls what we do and how we move so the corticospinal tract is our upper motor neuron you see on the right a diagram again don't get overwhelmed guys I'm going to simplify this this is our upper motor neuron and how this works is such so you have the primary motor cortex which descends down through the internal capsule through the well it is the upper motor neuron but through the upper motor neuron down through the medullary pyramids and at the medullary pyramid something really interesting happens the corticospinal tract will split into an anterior corner corticospinal tract shown there as a CST and into a lateral corticospinal tract shown as lcst and for the purposes of USMLE and comlex you really don't need to know that I've included it for completeness sake because the LCSC right that lateral corticospinal tract that's 75 to 90 percent of all of the upper motor neurons in the body and then those two corticospinal tracts or you can think of it as just the lateral if it's easier they will descend down go into the actual slice of the spinal spinal cord that controls a certain muscle in this diagram it looks like it's the bicep and then it projects into the bicep to actually control the movement so that is the corticospinal tract and again i told you that all you really need to focus on for the purposes of USMLE and comlex is the lateral corticospinal tract because that's really 90 percent of these neurons once the neurons descent into the lateral corticospinal tract they synapse at the anterior horn and this is really important because the lcst shown there in red is the upper motor neuron but the anterior horns shown there in blue on the left side of our slide here is the lower motor neuron and I'm going to assume that you know the difference between upper and lower motor neurons and if you do need a refresher in that topic I do have a video already created go search our inventory of videos and learn about the differences but it's really important in terms of the the type of pathology that you'll see if you have a lesion so if you lesion the corticospinal tract you'll get upper motor neuron signs but if you lesion the anterior horn which connects with the corticospinal tract you'll get lower motor neuron signs so go review that if you need to but this is the simplified corticospinal tract and how do we remember this well here is the mnemonic so you want to remember P P L M primary motor goes to medullary pyramids goes to lateral corticospinal tract which controls movement so when I think of the corticospinal tract I think of the corticospinal tract and then I asked myself what has spines well cactuses have spines and cactuses that have spines which reminds me of corticospinal tract are prickly plants and prickly plants lack moisture so you know that cactus is live in deserts and they are prickly plants because they have spines which reminds us of corticospinal tract and prickly plants lack moisture ppl M primary motor pyramids lcst movements I mean could the mnemonic get any more beautiful than that well it can if you look in this picture our cactus is actually splitting and I've drawn two yellow arrows on top of the cactus and what this represents is the splitting at the medullary pyramids remember that the medullary pyramids split the corticospinal tract into the anterior CST and the lateral CSC and I just put that in here so that you remember that the corticospinal tract technically does split but the really important thing here in this mnemonic is that prickly plants lack moisture ppl em it will help you remember what the corticospinal tract is and if you can remember the ppl em you'll remember that this is our upper motor neuron that controls movement is Flitz at the pyramids as shown by these yellow arrows and why do prickly plants lack moisture while they live in deserts and they have spines for corticospinal tracts so that is our corticospinal tract we are now two out of three tracks done let's talk about the last one this is the lateral spinothalamic tract and the lateral spinothalamic tract has historically given students the most headaches and I'm going to explain why so the lateral spinothalamic tract shown here on the right he's responsible for pain and temperature sensation but two to three segments below the level that gets injured and you'll understand what I mean when I talk about Browns two-card syndrome but the important thing to remember here is that it's going to manifest two to three segments below the level of the injury on the contralateral side with that in mind I want to pause for one second and talk about a super super high yield point that we need to talk about the two tracks that I already talked about before the lateral spinothalamic tract right we talked about the corticospinal tract and the posterior columns both of those tracks are itzá lateral so if you injure them the the deficit that they that they kind of lead to is going to be experienced on the same side of as the injury but if you contrast that with the lateral spinothalamic tract if we injure the lateral spinothalamic tract where the symptoms are felt on the body is on the contralateral side two to three segments below the level of the injury and again this will all make sense in just a few more slides but let's do an example to really hammer this home so the reason that you experience this the deficit which is pain and temperature sensation the reason that you experience that deficit two to three segments below the level of the injury on the contralateral or opposite side is due to something called lists hours track and less hours track is really just a track of neurons that carries the lateral spinothalamic neurons up two to three segments before they cross over and really connect back into the synapse that leads back up to the primary somatosensory cortex so here's an example to illustrate this let's say that we have an injury to c5 in the lateral spinothalamic tract on the right where you've experienced problems with the LST is two to three segments below which is c7 because we're two to three segments below c5 but on the contralateral side so because the injury was c5 right we experience the symptoms c7 left that's two to three segments below on the opposite side so that's the lateral spinothalamic tract and again just to really hammer this home for posterior columns and for corticospinal tract it is epsilon or which means same side on the exact same segment so if we were doing this example C 5 and we injured all of the tracks even though lateral spinothalamic tract is two to three segments below opposite side the posterior column manifestation of symptoms and the corticospinal tract manifestation of symptoms would be at c5 on the right because it's same level same side and then of course everything below it lateral spinothalamic tract is two to three segments below opposite side and everything below that so how do we remember lateral spinothalamic tract causing pain and temperature problems two to three segments below well lateral spinothalamic tract is LST which stands for lower segment three literally lower segment three LST two to three segments below the injury on the opposite side lower segment and then by three so if that confused you a little bit I'm gonna bring it all together now when we talk about something called Brown Sicard syndrome so I showed you at the very beginning of this presentation this is a cut of our spinal cord and you see all of these tracks going up to the brain and what happens if we do something like this we knock out literally one half of our spinal cord this is called a heavy trans section of the spinal cord and when we do this we knock out all three of the spinal cord pathways that we talked about right we knock out the lateral spinothalamic tract we knock out the posterior columns and we knock out the cortical spinal tract so we're going to have symptoms that coincide with problems with all three of these tracts so we need to do an example to illustrate how this is going to be presented to you on boards and how you solve these problems so here is our man that is going to be injured at the level shown therein with that thick black line so just for examples sake here let's say that our man gets injured he has a stabbing injury on the right side of his spinal cord at the level of t8 so that black line roughly at the level of t8 to his right so this the knife comes into his back and it completely heavy transects the spinal cord instantly severing connections from this corticospinal tract the posterior column and the lateral spinothalamic tract those are the three spinal cord pathways that are the highest yield that you need to know when this happens when you Hemme transect all three at once you get something called browns to card syndrome and Browns to card syndrome always has the same presentation so let's talk about what the presentation is and then relate it to these three tracks so we understand it so let's first label our three tracks that are going to be affected here so we have the corticospinal tract which I told you are the upper motor neurons the posterior column is responsible for discriminative touch and the lateral spinothalamic tract is responsible for pain and temperature sensation so how do I know that the LST is responsible for that opposite that contralateral area shown in green and posterior columns and corticospinal tracts are shown there on epsilon or guys both the corticospinal tract and the posterior column are apes so lateral pathways if you knock them out the symptoms are experienced on the same side as the injury so since this guy is being injured out on the right everything EPSA laterally will be for cortical spinal tract and posterior column LST stood for lower segment 3 so 2 to 3 segments below t8 which is roughly at t10 or t 11 on the contralateral side you get problems with pain and temperature and that's how I know that the LST is what's going to be experienced they are in green so if we label what these tracts do the corticospinal tract is our upper motor neuron symptoms right and again if you need help remembering what that is see our other video on upper vs. motor excuse me upper versus lower motor neuron symptoms but we're going to get upper motor neuron symptoms at everything below t8 because the injury is at t8 so the spinal cord is being knocked out of t8 so everything below th of t9 and down is going to experience upper motor neuron symptoms as far as the posterior columns are concerned while they are responsible for discriminative touch remember posterior column PC politically correct problems with discrimination so discriminative touch loss of fine touch loss of proprioception that's going to be experienced at everything from the level of the injury and down but on the EPSA lateral or same side again just to really hammer this home lateral spinothalamic tract LST lower segment three we drop down two to three segments go to the opposite side and that is where we have pain and temperature problems so this will be starting around t10 on the left so if they're giving this to you on us Emily your complex how this will work they will tell you that a patient suffers some type of injury they might tell you that the spinal cord is heavy transected if they're being really generous but they don't have to what they'll do is they'll give you the findings so they'll say patient has loss of pain and temperature sensation at the level of t10 on the left patient has blah blah blah they'll describe upper motor neuron symptoms at everything from t8 down they'll tell you that the patient you know has decreased pinprick sensation which is a way of saying that they have decreased discriminative sensation at the level of you know t8 and down and you need to put these findings together and figure out where the injury is because the question can either ask you you know at what level was the spinal cord heavy transected or maybe they'll give you the corticospinal and posterior column findings and then say at what level will you experience pain and temperature problems so you need to go two to three segments down contralateral side and as you can get as you guys can probably see here it kind of turns into sort of like a math problem you got to figure out where the injury is and then where your corresponding symptoms are but in review these are the three highest yield spinal cord pathways corticospinal which is upper motor neuron posterior column which is discriminative touch and discriminative sensation because remember PC posterior column politically-correct don't discriminate and then lateral spinothalamic tract is pain and temperature but three segments down on the opposite side because LST lower segment three so I really hope that this was helpful for you guys and that was extremely high yield so I do wish you the best of