thanks for tuning in please like subscribe and check out my instagram for cool science and not science stuff and a big thank you to my patrons on patreon for your contributions to my channel welcome back to anatomy and physiology on catalyst university my name is kevin tokoff please make sure to like this video and subscribe to my channel for future videos and notifications in this video we're going to talk about a series of afferent pathways that take sensory information to the brain and these are collectively called the cerebellar tracts but before we get into that we need to have a basic understanding of proprioception so i'm defining proprioception as the conscious and non-conscious awareness of body position and velocity in space with respect to time so that's a mouthful right there but it basically boils down to two things one knowing the spatial and temporal location of each piece of the body and the body as a whole and then using that information to coordinate the moves of the body to create a coordinated movement now there are two sets of proprioceptive pathways that go to the brain the first is the conscious proprioception pathway and this is the dcml pathway dorsal columns medial limniscial pathway we talk about that in a separate video this is proprioceptive information that you are consciously aware of so take this picture down here at the bottom from star wars empire strikes back so on the left here you have this guy and he's got his eyes open now to truly rely on proprioception we really should have our eyes closed here he has his eyes open and he can clearly see any part of his body that he looks at and therefore knows where it is in space so if he closes his eyes i guarantee you he still knows where his arm is in space and where his hand is because proprio receptors within the muscles and the joints all throughout his right upper extremity here are sending information to the brain and then his brain is able to deduce where the arm and the hand are in space and you can do this for yourself just close your eyes and move your arm or your leg into a different position than where it was originally and assuming that you don't have any serious conditions that might impact the cerebellum and these pathways well you know where your arm is you know where your leg is you know where all the parts of your body are the awareness of that is conscious proprioception and that's the dcml pathway another example of conscious proprioception would be if you're at your house at night and the power goes out and it's pitch black in your house and you can't see well vision has obviously been removed there and we know that when we can't see it all because it's dark we're gonna have our arms along trying to feel along the walls they're going to be in the air reaching for things we really need to have the awareness of where our legs are so we don't trip over things and so that's another example where we would be heavily relying on that conscious proprioception but there's of course non-conscious proprioception to understand non-conscious proprioception take a look at this exercise right here this is a deadlift and to some people it may not seem so but it's actually a very complicated movement that involves many different joints of the body all moving to certain extents and also certain muscles contracting to certain extents but let's say you go in to do this lift and you are attempting to get a new personal record when you go into that lift you are not thinking about the position of your ankle joint in space whether it's dorsiflex neutral plantar flexed throughout the duration of the movement you're not thinking about the relative position of your knee joint or the hip joint the angles of them the tension in the muscles right you're not thinking about all that stuff but yet as you go from the start position to the final position here your brain is very aware of the tension in some muscles the stretch in other muscles the angle of joints the velocity of movement of particular parts of the body and even the acceleration of those parts of the body you don't need to be aware of those things but that information that is non-conscious proprioception and your brain takes that information and it can modify it in certain ways it can make error correction during a movement and it basically gives you this nice coordinated movement that you see here in the video another example that you may not think about is something as simple as walking now we know you move the right leg forward then you move the left leg forward and so on and so forth but as you walk around your office or at school or if you're running even you're not thinking about the position of your ankle the position of your knee the position of your arms and so on and so forth that information though is still going to the brain and it's being integrated there where error correction can be made modulation of certain muscles can be and so on and so forth that information from receptors in muscles and joints that is taken to the brain via the spinal cerebellar pathways let's take a look at those pathways right now so on the right side of the screen right here this is a cross section of the central nervous system at the bottom here we have the spinal cord but this is a lower part of the spinal cord basically below the level of t6 then up here is a more superior cross-sectional region of the spinal cord this is an upper part of it above t6 and then you go up from the spinal cord you reach the medulla oblongata and then up here's the pons but remember posterior to both the medulla and the pons we have the cerebellum so here's our medulla part of the brain stem and posterior to that is all of this tissue which is our cerebellum the same thing goes for the pons here's your ponds right here and then you have the cerebellum that is posterior to that okay and all these colored fibers right here that you see in blue purple red and green these are all different tracks that are collectively the spino cerebellar tracts and the way to think about the spinal cerebellar tracts is to understand whether that information comes from the lower extremity or the upper extremity and whether or not that proprioceptive information is coming from golgi tendon organs or from muscle spindles now remember muscle spindles relay information to the central nervous system via sensory efferent fibers that are type 1a so 1a goes with muscle spindle whereas golgi tendon organs or gtos these relay information to the central nervous system via sensory afferents that are type 1b and so you just mix and match and you get the four major spinal cerebellar tracts so if we look down here at the 1b fibers here in green that are coming from the lower body or generally the lower extremity they're basically entering here through the spinal nerve and then through the dorsal root ganglion and then they come in through the dorsal roots into the spinal cord and that's where the synapse with the second order neuron comes so notice there's a synapse right here then the second order neuron actually crosses over to the opposite side of the spinal cord at the same level so if this were a 1b fiber that was coming in at the level of let's say t9 well then it would enter the spinal nerve a t9 dorsal root ankle and a t9 and then it would synapse with the second order neuron also at the level of t9 and then it crosses over to the other side also at the level of t9 i think i've hit that point to death and then that second order neuron is going to ascend upward to the cerebellum as the ventral spinal cerebellar tract it's ascending up ascending up and up and up it goes past the medulla and ultimately is going to enter the cerebellum at the level of the pons through what we call the superior cerebellar peduncle okay this is the only one of these tracks that's going to enter the cerebellum through the superior cerebellar peduncle the other three are going to enter through an inferior peduncle and then as you can see here once in the cerebellum those second order neurons are actually then going to re-cross over back to the ipsilateral side so there's one crossover here in the spinal cord another crossover in the cerebellum so ultimately this is still ipsilateral control so while we're on the lower body or the lower extremity let's look here at the 1a fibers here in purple these sensory afferents are going to enter the spinal nerve and then they're going to go through the dorsal root ganglion through the dorsal root and they're going to synapse here with second order neurons again at the same level of the spinal cord but these don't cross over they remain ipsilateral the whole way so the second order neuron is then going to ascend up the spinal cord and ultimately into the brain stem and it does so as the dorsal spinal cerebellar trapped so it's going to ascend up here you can follow it up in purple and once it gets to the level of the medulla it's actually going to enter into the cerebellum at that level through something called the inferior cerebellar peduncle this is one of the three major spinous cerebellar tracts that enters through that inferior cerebellar peduncle into the cerebellum the other two that we're about to mention also do this okay and so the ventral and dorsal spinal cerebellar tracts these are the two tracks that ultimately sense proprioceptive information from the lower body now i know i said lower extremity here it technically is the lower body because it is below t6 and so we probably have the hip girdle musculature some abdominal musculature and so on and so forth but again it's the lower body but we're just simplifying it by saying lower extremity okay now on to the upper extremities these are the rostral and the cuneo cerebellar tracts so let's start with the blue one here this is actually sensing information from golgi tendon organs the 1b sensory afferents here in blue so again these are coming above the level of t6 so upper extremity so we follow it in here through the spinal nerve through that dorsal root ganglion through the dorsal root into the spinal cord and again that snaps happens at the same level of the spinal cord and then it synapses with the second order neuron right here but it doesn't cross over to the other side in the same way as the dorsal spinal cerebellar tract here in purple instead that second order neuron remains on the same side of the spinal cord and ascends up as the rostral spinal cerebellar tract and you can see it ascend up and up and up and up and it's eventually going to cross into the cerebellum at the level of the medulla through that inferior cerebellar peduncle okay and then it goes into the cerebellum that's the rostral spinal cerebellar tract and the last one here to talk about is the cuneio cerebellar tract so that's this one here in red that's detecting proprioceptive information from muscle spindles in the upper extremity or upper body so in red here we see that this one is going to enter the spinal cord through the spinal nerve the dorsal root ganglion right here but something different happens with the cuneo cerebellar tract so instead of actually synapsing in the spinal cord it's going to come through here this dorsal root into the spinal cord and then it's going to ascend upward and then you see here that the first order neurons which are the sensory efferents right here they're going to synapse with the second order neurons here in what's called the lateral or accessory cunate nucleus this cluster of cell bodies is really the synapse between the sensory afferent and the second order neuron right here and the second order neurons as they go up further those are going to be the cuneo cerebellar tracts and so ultimately what you can see here is that the cerebellum exerts control always over the ipsilateral side of the body it's more obvious with these ones over here in red purple and blue but remember that with the green pathway over here it's a little more complicated we have one cross over here at the level of the spinal cord but then there's a re-crossover back to the other side here in the cerebellum and so that gets it back to the ipsilateral side and so those are the four major spinal cerebellar tracts we divide them up as to whether or not they sense information ultimately from the lower body or upper body and whether they come from sensory ethernets of 1b type or 1a which implies golgi tendon organs or muscle spindles so hopefully this made sense to you please make sure to like this video and subscribe to my channel for future videos and notifications thank you