hello and welcome to one metro we discuss concise medical knowledge that you can fit inside of a bun in today's video we're going to be having a look at the different spinal tracts putting a focus mainly on the sensory and motor tracks of the spinal cord with that said let's get into having a look at what the tracts actually do and how they link together with the nervous system let's start at the very beginning we know that we can break down the nervous system into two different parts the central nervous system which compromises of the brain the brain stem and the spinal cord and also the peripheral nervous system which consists of the spinal nerves or the part of the somatic nervous system and the autonomic nervous fibers as part of the autonomic nervous system now we know that in order to interact with our environment we need information to go to our brain and in order for us to act on the environment infinite nation needs to travel down our brain into our area that we need to move so let's use an example say we're petting something like a fluffy animal we need to send the information that this is fluffy and the other sensations that we're feeling in our hand from our hand to our brain and we send this information first to the spinal cord and then upwards towards the brain the brain can then process this information and after a while once we've finished petting it it may want to move our hand away and thus it needs to send information down towards and through the spinal cord to our hand telling us to move us away there we saw two examples of two different pathways the first was the ascending pathway in green where we carried sensory impulses up towards the brain and then we saw a descending pathway where our brain told us to move our hand away and thus motor information traveled down the down the spinal cord and as such we can say that all sensory information generally ascends towards the brain as we take information from our environment and center up to the brain and all voluntary motor impulses descends down from the brain telling us to carry out certain actions with that said let's now break down the ascending and descending pathways and in fact let's actually break down the sensory pathway first so in terms of sensation we have quite a different types of sensation and they can be generally grouped to some different pathways let's start with crude touch pain and temperature and these three are part of the spinothalamic pathway the pathway that links the spine to the thalamus or the spinal cord to the thalamus other sensations we can also experience include things like fine touch vibration and proprioception and this is dealt with by the dorsal column and medial lemniscus pathway now i know these words sound quite scary but let's just orient ourselves with the spinal cord and see how this fits in here you can see we have a cross section of the spinal cord with the dorsal side around here and the front side or the ventral side around here the spinal thalamic pathway actually is located anteriorly and laterally in other words around the front and slightly to the side around this area here and as a result it's called the ventro lateral spinothalamic tract ventro lateral essentially referring to exactly where in the cross-section it lies and spinothalamic tract as it connects the spinal cord to the thalamus the dorsal column medial limbiscus pathway the dcml lies more dorsally and you can see it here in blue so now let's have a closer look at exactly how nervous impulses travel through the spinothalamic pathway first and then the dcml here you can see we have a more extended picture of the spinal cord and a cross section and we can say that we we can label a few other features such as the dorsal ramus the dorsal root ganglion with some of the cell bodies of the sensory sensory cells or sensory nerve cells of our peripheral nervous system line our dorsal root and at point of entry to our spinal cord we have the dorsal horn as well information such as temperature pain and crew touch come in through our dosal ramus to our grossel root ganglion and finally into our dorsal horn now here's the interesting thing at the dorsal hole and at the point of entry the ventral lateral spinothalamic fibers actually cross to the contralateral side to the contralateral ventral lateral spinothalamic tract contralateral essentially meaning to the other side and from this point on they can be projected upwards towards the brain these projected fibers then make their way to our brain specifically to the thalamus which collects all of the sensory input from all of our external environment and from the thalamus these signals can then be sent to the somatosensory cortex where the brain can make sense of exactly what we're feeling where we're feeling it and associate it with other things in our environment so as a quick recap we can see the information once it enters the dorsal horn the fibers cross over to the opposite side the process of crossing over is called decussation to the contralateral side it travels up the spinal cord to the thalamus and they're finally projected to the somatosensory cortex how can we make this more clinically relevant well we know the decussation point is or the crossing over point is at the point of entry at the spinal cord and as such if the spinal cord is damaged because the fibers cross over we are going to see symptoms appear on the opposite or the contralateral side i hope that makes sense what about the dorsal column medial lemniscus pathway so here we have the exact same picture this time but we have a different set of inputs that of vibration proprioception and fine touch and this time we have the information enter again the exact same way through the dorsal horn but instead of going to the ventrolateral spinothalamic pathway it instead goes to the dorsal column giving it the name dorsal column medial lemniscus pathway and in fact this area of the dorsal column can be broken down into two parts the fasciculus cutaneous which deals with most of the upper body sensation and the arms and the fasciculus gracilis which deals with most of the lower body now how can we remember that well a good way i've found of remembering it is when you think of the word fasciculus cutaneous i want you to think of a cute baby and when you see a cute baby you want to pinch it and in order to pinch a baby's cheeks you need to use hands so therefore that sensation the cutaneous sensation is done for your hands and for your upper body by the fasciculus cutaneous when it comes to the fasciculus gracilis i want you to think of a ballerina and ballerinas are generally quite graceful on their feet and therefore we can say the sensations of our feet specifically of the ones mentioned before is done by the frasiculus gracilis like a graceful ballerina from here the impulses can once again be projected up the spinal cord but here's where they vary once projected up towards the spinal cord the dcml pathway actually encounters the medulla first and at the medulla the signal is sent over to the contralateral or opposite thalamus and finally projected to the somatosensory cortex where we can again make sense of things notice how this is significantly different from the spinothalamic pathway as it does not cross at point of entry but crosses at the medulla at the side here i've also got a very quick recap so you can see it enters the spinal cord it goes up the spinal cord it decorates in the medulla to the contralateral thalamus and then finally to the somatosensory cortex so how can we make this clinically relevant well we know the decoration point for both of these is the medulla and as such if we have the spinal cord damaged we're going to get the same side of symptoms and that's ipsilateral so if we had the spinal cord damaged here we're going to notice symptoms on this side so putting it all together in blue you can see we have the dcml pathway in green we have the spinothalamic if we have and we have a quick uh table summarizing all of these details on the left if we have damage to the brain in the case of a stroke we are going to get contralateral symptoms as both of these will eventually cross over however if we have damage to the spinal cord then we're going to get contralateral loss of pain and temperature loss because remember it crosses over an ipsilateral loss of vibration and proprioception as the dcml fibers cross at the medulla now that we've got a good idea of sensation let's talk about movement movement and the nerve fibers for movement are mainly carried by the corticospinal tracts the corticospinal tracts essentially runs from the cortex of the brain and down the spine and in fact the process starts off in the motor cortex as we said and the impulse is sent down the internal capsule this white sort of column you can see between these gray structures from the internal capsule they are projected down to the medullary pyramids and once again at the medullary pyramids they cross over to the opposite side and make their way down the spinal cord to the anterior horn cells in the spinal cord from this point on they can leave the spinal cord becoming a spinal nerve and as you can see in the quick summary we start off with the motor cortex unlike before we cross over at the medulla and we go up the lat down the lateral uh corticospinal tract to the anterior horn cells and to the spinal nerves so making it clinically relevant our decision point is once again the medullary pyramids and thus if we have damage to the spinal cord we're going to see the same side having symptoms so let's put all of this into some clinical relevance and just for ease of purposes i'm going to draw in the three tracks so in blue we can see we have the dcml in green we have the spinothalamic and in red we have the corticospinal motor tracts if we have something like a stroke we are going to get global and contralateral loss of all three because remember all three would have crossed over at some point if however if we affect only half of the spinal cord say for instance we affect the left hand side in this case of the spinal cord then we're going to see ipsilateral or same-sided loss of motor and vibration and proprioception sensors but remember because the fibers cross over our pain and temperature sensation is going to be intact as they are coming from the right hand side and this is a this is a specific syndrome that we call brown cicada syndrome so just to clarify we have ipsilateral motor and vibration and proprioception loss and normal pain and temperature sensation on that side and we get contralateral loss of pain and temperature on the other side okay what about a different case what if we had something like a syringe or a fluid filled space build up in our spinal canal causing it to be extended well what are we seeing in the early stages well we can see the main thing that is affecting is that crossing over of the spinothalamic tracts and as such we can say that the um it's going to be mainly the pain and temperature sensation that's going to be affected as they're the ones that cross over directly across that area and look because it's directly in the middle it's going to affect both the right hand side and the left hand side so what we're going to see is a bilateral loss of pain and temperature sensation but what about vibration and proprioception well we can see that the vibration and proprioception synthesis goes around the dorsal column and not near this area and therefore it's generally intact this it can be seen in a condition such as cyringomelia and often the very first thing that patients complain of is the characteristic cape-like distribution of pain and temperature sensation loss and they may present with something like burning their hands without meaning to that concludes the video hope you guys found it useful please feel free to share and subscribe and if you have any 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