Cerebellum Anatomy & Function

Hi Ningeniers, in this video we are going to talk about the cerebellum. So let's go ahead and dig into this. Alright, so what we're going to do is we're going to start off with the cerebellum and we're going to look at it in three different views. We're going to look at it in kind of an anatomical lateral view, then we'll look at it in a posterior view. We'll cover the anatomy, but this is going to be more for the functional anatomy. Then what we'll do is we'll take a slice of the cerebellum and look at the internal circuitry of it, specifically the deep cerebellar nuclei, and then we'll go into a lot of the pathways associated with that. So first thing, just in general, cerebellum, it sits within the posterior cranial fossa of the skull. Remember that, anatomy-wise. It's separated from the cerebrum by a dural septa called the tentorium cerebelli. Another important thing about the cerebellum, is when you look at it, you're going to notice that it has these things called folia. Folia are just kind of like little folds. That's basically what they are. And what they are designed to do is to increase the surface area of the cerebellum. So if you notice here, I kind of made this like squiggly dark line there. That is particularly, that's pertaining to the outer gray matter of the cerebellum. The gray matter, you guys should know, is unmyelinated cell bodies or dendrites. In the center of this actual cerebellum, we have what's called the tree of life or the arborvitae. This is important because it contains the myelinated axons of multiple fibers that are connecting the cerebellum to the brainstem, to and fro. All right, so it can be from the brainstem, from the cerebrum, from the spinal cord, from the inner ear. We'll talk about all these pathways, which is extremely interesting. And then again, we'll talk about some of the deep cerebellar nuclei associated here. First things first, we have the two particular fissures which separate the cerebellum into their structural lobes. So the first one we're going to do like right here. We'll do that one. That's called the primary fissure. We have another one which is right here and that is going to be the posterior lateral fissure. Okay so we have these two fissures here primary fissure and posterior lateral fissure. Same thing we'll talk about it over here and we'll highlight that. What I want to do is we have three lobes that are anatomically separated from one another. We're going to do this first one right here, this green. This is going to be a particular lobe, more of a primitive area of the cerebellum, and they call this area the flocculonodular lobe. Okay, we'll talk about its functional name whenever we get to this diagram. Another lobe is going to be here. This is a really, really big one and this is called the posterior lobe and this is more of the newer more modern part of the cerebellum. We'll talk about its functional name in a little bit. And then we have this other one up here and this is going to be the anterior lobe. And again we'll talk about its functional term here as well. So we know the outer gray matter, we know the white matter, the arborvitae, we have the folia separated by the dentorium cerebelli, little brain, right? And we know that we have these primary fissure, posterior lateral fissure. anterior, posterior, and flocculonodular lobe. The next thing we need to understand about the cerebellum is just the basic thing that I want to get us started with because it's going to help us throughout the process of this entire video is what is its functions. I want you to remember, there's a bunch of them, but I want you to remember specifically the first one is balance and equilibrium. Okay, so we'll kind of put these separately. Balance, equilibrium. Now, where does that come from? We're not going to go into a ton of detail because we'll go into that a little bit later, so I'll save it for that. But what I want you to remember is this is connecting. The cerebellum is connected with the inner ear. So what we're going to do is we're just going to say here's our inner ear for right now. We're not going to go over the semicircular canals and all that stuff like that. But the inner ear is connected to the cerebellum. And we'll talk about the actual vestibular cerebellar tract. But the inner ear is carrying with it balance and equilibrium from the semicircular canals, right, which has the crista ampullaris and the vestibule which consists of the macula. Okay, the next thing that it plays an important role is for muscle tone. So it plays a role within our muscle tone. So let's write that down. So muscle tone and it also plays a role in the coordination of our movement. So muscle tone and coordination. And it plays a really, really important role in motor learning. So what do I mean here? I'll explain. So I want you to remember this. Balance and equilibrium, muscle tone, coordination, motor learning. These are the really important things that are controlled by the cerebellum. We know the inner ear is respect to the balance and the equilibrium. Okay? The muscle tone is particularly through specific pathways, spinal pathways. So if you guys remember, we've gone through a lot of these. This is going to be from your proprioceptors. Proprio. receptors. Your Golgi tendon organs, your muscle spindles, your joint capsules, all of those structures they're picking up proprioceptive information if you don't know what proprioception means. Your position of your muscles, your joints, your tendons, your ligaments, all of those in a three-dimensional space. Your awareness of where you are. It takes that information and sends it to the cerebellar cortex. The cerebellar cortex receive information from your inner ear, your proprioceptors and here's another important thing. It also receives information about the motor plan. What kind of movement your cerebral cortex is going to execute. So you have some specific areas here. If I were to kind of highlight here, we're not going to go into crazy detail, but remember you have your central sulcus. What's some of the big areas here around the central sulcus? Let's do this in this color here. Remember here behind it you have the Primary somatosensory cortex. In front of it you have the primary motor cortex. You have the supplementary motor area. You have the premotor cortex. All of these areas are associated with the actual motor planning, specifically sending down descending axons. These are your upper motor neurons. They'll send fibers down where? Look, let's say that we just take it from any of these. Here's your upper motor neuron. It'll come down. Go to an area of the spinal cord to the ventral, the anterior gray horn, activate a lower motor neuron which will go out to what? To a muscle, right? Let's draw here our muscle. Go out to a muscle, right? So we know that the cerebral cortex is responsible for sending down these upper motor neurons down to a lower motor neuron, activating a muscle to cause it to contract. While it's sending these pathways down, guess what it's doing? It's letting the cerebellar cortex know of these things. So it's saying, hey, cerebellum, I have some motor plans that I want to coordinate. I want you to be aware of that. So now the cerebellum is receiving information from the inner ear about balance, equilibrium. It's receiving information about our proprioceptors all throughout our entire body. It's receiving a pre-programmed motor plan, which has already gone through another structure, not just the cerebral cortex, but the basal ganglia. And it's sending this information down to the cerebellum. He's going to coordinate that. He's going to develop a perfect, perfect calculated plan and a blueprint. And then from there, it's going to say, okay, I think we have the perfect thing. What I'm going to do is I'm going to let you know what I think you should do. And we'll talk about all these pathways. This is just a general overview of what we're going to talk about, okay? So we have an idea here of what the cerebellum's anatomy is. We have a basic idea of its function. Let's go ahead and let's get into a little bit more detail on the functional anatomy of the cerebellum. What we're going to do is, I'm going to take the cerebellum and I'm going to unfold it. And I'm going to look at it in a posterior view. So this is going to be a posterior view. And we're going to cover the, again, the anatomical components here. But what I want to do now is I want to kind of start switching over into more of a functional anatomy. So again. To give you guys an idea, remember we said that the anterior, so this is going to be anterior lobe, posterior lobe, flocculonodular lobe. All I'm doing is I'm just unfolding it. Okay, so here, let's write these down. The three lobes, we're going to coordinate it with the colors. So this top lobe up here, which is this top lobe, that's going to be, so again, coordinating this, anterior lobe, anterior lobe. We'll write this one up here. So anterior lobe. Okay. Next thing, this bottom one down here is this one right here. That's the posterior lobe. So we'll have that in this purple color. And then this last one down here, which is tucked into this little area here, this green, that's our flocculonodular lobe. Such an interesting one. That is the flocculonodular. Nodular lobe. So, flocculonodular lobe. You know the flocculonodular lobe is actually one of the most primitive of all of them. It's also referred to, and we'll talk about it in a second, called the vestibulocerebellum. Also called the archicerebellum. It's a very, very primitive area of the cerebellum. Okay. So, we have the coordinating lobes. And again, I told you I was going to mention those fissures, so I don't want to forget about those. This fissure here, which is separating that one right there. Again, same thing. This is particularly the . Primary fissure, so primary fissure. Separating the anterior lobe from the posterior lobe. And then remember this one right here is going to be the posterior lateral fissure, separating the posterior lobe from the flocculonodule lobe. So posterior lateral fissure. Okay, good deal. Now that we've gotten the idea of our anatomical lobes, we want to look at them in a different way. Now we're going to look at it in a functional area, functional zones. So we have three different functional zones coordinating respectively with the corresponding lobes. Here's the first thing. The anterior lobe is also called the spinocerebellum. So let's write this down. So when we talk about the anterior lobe, another specific one for this functionally is called the spinocerebellum. Now. When we talk about the spinocerebellum, here's the tricky thing though. It is particularly occupying what's called the vermal zone. So you know when you're looking at the overall anatomy of the cerebellum, you have the lateral hemispheres and then you have the vermis. The vermal area, this is your vermis right here, the central piece right here. The vermis is primarily going to be a part of the spinocerebellum. So what I'm going to do here is we'll have this part here. is going to be a part of the spinocerebellum. It also has some nuclei here that we'll talk about in a second when we get there. Going on the sides of that, what I'm going to do is I'm going to kind of make like a little dotted line here. We have another area which is important for the spinocerebellum. And this is on the sides of the vermis. So what does it mean when it's on the sides? So this is the vermal zone. This area over here is the paravermal zone. We also give it another name which is the intermediate zone. So when I talk about the spinal cerebellum, I want you to remember three components of this. It occupies the vermal area and the paravermal area. Another name for the paravermal area is the intermediate zone. Now here's the important thing with this. What I say spinal cerebellum does, it picks up sensory information. So don't, like in the cerebrum, don't we have a sensory homunculus? Guess what? We got a homunculus for the cerebellum. So, how does this generally work? Well, what we do is we're going to look at it from up in this top lobe and then this bottom lobe. Okay? There's this kind of sensory homunculus, and here's how it kind of goes. Don't laugh because it does look funny. It looks like a little alien. But in general, we start off here. In the vermis, it's mainly for the axial part of our skeleton, our axial musculature. So what you'll see is you'll see the trunk. You'll see the neck and you'll see the head. But the head kind of also spreads out and kind of splurges over into this paravermal area as well. More of the temporal parts here. And here, let's put a little smiley face for the guy, a little bit of hair, right? So, if you look here, the trunk, the neck, and aspects of the head is occupying the vermal zone. So, the vermal area is primarily getting sensory information from the trunk, the neck, and the head. The extremities, let's put here, here's his lower leg, here's his other lower leg, here's his upper extremity, and here's another upper extremity. This is going into the paravermal area. So the paravermal area of the anterior lobe is particularly taking sensory information from the upper and lower extremities and certain aspects of the lateral head. Now, the next thing is for this bottom part down here in the posterior lobe. There's another aspect, there's another sensory homunculus. But this sensory homunculus is kind of odd. How it works is you have two little homunculi back to back with one another. So now what I'm going to do is I'm going to have the head here, I have the little nose, here's like a little face. We'll have another one here. And then here's going to be their trunks, here's his trunk. And then coming out here is going to be this arm, this arm. This leg, this leg, this arm, this arm, this leg, and this leg. This is going to be the sensory homunculus for this bottom part, for this vermal and paravermal zone within the posterior lobe. Okay? So when we're looking at the sensory homunculus, it is really important just to understand that within the vermal area is going to be the trunk, neck, and the head. And then for the paravermal or intermediate zone, it's going to be for the upper and lower extremities. Okay? Boom. We beat that like a dead horse. Now, we go to the next part, posterior lobe. Posterior lobe is mainly going to be occupying this functionally. Functionally is going to be this area over here. So now, just take all of this and just highlight this. This is going to be the lateral hemispheres. So this is primarily, the posterior lobe is going to occupy the lateral hemispheres. So let's write this down here, lateral hemispheres. So this is the functional. areas of it. And we'll talk about a really, really important nucleus in this area called the dentate nucleus. Mmm, it's going to be good. All right, next one. We go to the flocculonodular lobe. That's this little guy. We unfolded him. Remember, it's separated to be the posterolateral fissure. Well, you have this area here, so you have the nodulus, and then you got your flocculus over here, these little flocculus. This is important because it's believed to be important with respect to the vestibulocerebellum. So they believe that this is particularly related to what's called the vestibulocerebellum. So, vestibulocerebellum. And this is going to be picking up information from your vestibular system. Now, I forgot to mention here with the posterior lobe. Remember we said vestibulocerebellum for the flocculonodular lobe. Spinalcerebellum for the anterior lobe. Another really important one that we got to mention here for this posterior lobe is this is going to be what's called the cerebrocerebellum. And this is going to be connecting the cerebrum to the cerebellum. Now, let's make sense of all this really quick before we move on. Spinal cerebellum, it's this proprioceptive pathway, right? That's all it is. And it's taking it from the proprioceptors of our trunk and our extremities. Boom. Going to the vermal, paravermal areas. Post-ear lobe, it's going to the lateral hemispheres. But where is it coming from? From the cerebrum. It's this motor plan going here. Floculo nodular lobe, vestibular cerebellum. Where is it coming from? Inner ear. Isn't it cool to see how all of this stuff is kind of coordinated perfectly? Okay, so we have an idea of the general anatomy. We have an idea of the functional anatomy as well as what these general things are responsible for. Now what I want to do is we've got to dig a little bit deeper, unfortunately. I'm going to take a slice of the cerebellum, and we're going to look into the cerebellum at some of the deep cerebellar nuclei. Okay? Now, when we're looking at these, we're going to look at these from the lateral hemisphere. into the actual central part or the medial aspect here, right? I like to use a mnemonic to memorize these. So I go by don't eat greasy food, okay? Don't eat greasy food. So how this works is don't eat greasy food. The first nucleus here is going to be the dentate nucleus. Let's do this here with red. So the first one is going to be the dentate nucleus. And remember, which hemisphere did I say it should be associated with? The lateral hemisphere. I want you to remember that. Lateral hemisphere. You'll see that this is a really important structure because it connects with the red nucleus and the thalamus. The next one is these two. The bluish and purplish. So let's write these down. We're just going to do it in blue, but realize it's the same for both of these. Actually, I got an idea. We're going to call these the interposed, look at this, nucleus. The interposed nucleus is made up of two components. Remember, don't eat. Eat, this blue one, is the emboliform nucleus. So we have the emboliform nucleus. Don't eat greasy globos. So this is going to be your globus nucleus. The globus nucleus and the embolyform nucleus make up collectively what we call the interposed nucleus. Now, this is going to be primarily where? The paravermal and vermal area. Makes so much sense, right? So again, this will be occupying the vermal and paravermal area. Let's write that here, that this will be occupying the vermal. and paravermal area. Okay? The last one is don't eat greasy food. This is for the fastigial nucleus. So this last one here is called the fastigial nucleus. The fastigial nucleus is located in the center, but what I tell you... The flocculonodular lobe is responsible for the vestibulocerebellum. The vestigial nucleus is primarily connected with the flocculonodular lobe. So I want you to write that one down. That one is associated with the flocculo. Nodular, this makes this a little bit nicer here for you guys. Nodular lobe. Here's one more thing though. They've also found research. that it's not just in the flocculonodulo, but it also the fastigio nucleus is in the vermis. So I don't want you to forget that one, but you can also write down on the side there it's also in the vermis. I'm going to put here, we'll put here on the side, plus vermis. Okay, so we have our structures here and I want you to remember the mnemonic. Again, how does this mnemonic go? Don't eat greasy. food, don't eat greasy food. And this is your deep cerebellar nuclei, okay? So before we start going in now and looking at how these deep cerebellar nuclei connect with our pulmonary receptors, our inner ear, our cerebrum. I want to do a super quick recap. Again, cerebellum, really important structure. What does it do? Balance, equilibrium, muscle tone, coordination, motor learning. How does it do all this? Connects with your spinal pathways via appropriate receptors. Connects with our inner ear via the semicircular canal in the vestibule. Connects with our cortex based upon the pre-organized motor plan from these cortical areas. Takes all that, integrates it in coordination with the basal ganglia and sends it back up to the cortex with the perfect calculated motor plan. If we take it, we have the primary fissure and the posterior lateral fissure. Anterior, posterior, flocculonodular lobe. Looking at it in the functional anatomy, the lateral hemispheres are going to be particularly for the posterior lobe, right? The cerebrocerebellum. The vermal and paravermal area is going to be for the spinocerebellum of the anterior lobe. And the flocculonodral lobe is going to be specific for the vestibulocerebellum. If we dig in deeper and correlate the nuclei with these functional lobes, we have the dentate nucleus with the cerebrocerebellum, right? But specifically, the lateral hemispheres. The interposed nucleus, which is the... Interposed nucleus is the globus and emboliform nucleus. These are going to be related with the spinocerebellum. And they are going to be... taking into consideration the vermal and paravermal area. And the vestigial nucleus is the flocculonodulo, which is the vestibulocerebellum, which is connected with the inner ear structures. So now that we have a pretty good idea of that, what we got to do is we have to take and say, how does these nuclei interact with these fibers coming in or these fibers going out? Okay, so let's go ahead and do that. Alright, so now we already said that we're going to dive into the internal circuitry. So to give you a little bit of an idea, just of what we have here, we separate the cerebellum, particularly the cerebellar cortex. Remember, what did I say? The cerebellar cortex is consisting of what? Cell bodies and dendrites. Cell bodies and dendrites. Now, remember I told you that there is some gray matter lodged in the center of the cerebellum. What were those called again? Deep cerebellar nuclei. Don't remember the mnemonic? Don't eat greasy food. Dentate, emboliform, globus, fastigio. We're going to represent the deep cerebellar nuclei by one nuclei, but just realize that this could be for all of them. It's not just for dentate. It's not just for any, like one specific one. It is for all of them. This internal circuitry is for all of them. This green one is going to represent our deep cerebellar nuclei. What I'm going to do is I'm just going to put the save room because we're going to need it. I'm just going to put DC in. And I want you to remember that that is our deep cerebellar nuclei. Then I told you that there's white matter, which is going to be connecting all the way up to the cortex, the cerebellar cortex. And here's what I want you to remember. We said that the cerebellar cortex is cell bodies and dendrites. Look at all these. What we're going to do is we're going to separate this into three layers. The subrheal cortex is three layers. Going from top to bottom. The first one that we have here. is you're going to have the molecular layer. So this is going to be the molecular layer. And we're going to have two important cells in this area, and we're going to talk about them called the stellate cells and the basket cells. We're also going to have the parallel fibers of the granule cells too. The next one is we're going to have the Purkinje layer. So this is our Purkinje layer. And then this one is nice and easy to remember because guess what? The Purkinje layer is consisting of the Purkinje. neurons, so the Purkinje cells. And this last layer here, which is going to be the most inner layer, is going to be the granular layer. So this is the granular layer. So we got three layers of the cerebellar cortex from outer to inner. Molecular, Purkinje, granular, and then if we go to the center of the actual cerebellum, we have the deep cerebellar nuclei. Dentate, embolyform, globose, and fastidio. Now, What we have to do is we have to see how if we have fibers coming in to the actual cerebellum, how it organizes all of these internal circuitries and determines which one is the most important signal. Big thing I want you to take out of all this, because this is a lot. The big thing I need you guys to take out of all of this is that all of this internal circuitry is important for what's called neural sharpening. Okay? So it's extremely important with respect to what's called neural. Sharpening. You're going to see a lot of things going on here. The neural sharpening is making sure that the most important stimulus is taken care of at that point in time. Okay, so we're trying to make sure that every signal that we send out of the cerebellum has the just perfect amount of Perfect plan for movement. It's not going to be over amount. It's not going to be an under amount It's going to be just the right amount. So how does this work? First thing we have to do is remember I said we have fibers coming in the cerebellum has fibers coming in through a couple different areas one important one that I want you to remember is from the inferior olives. So let's write that down over here. Let's do this one in this blue. So we're gonna have inferior olives. I'm gonna put these right here, inferior olives. If you guys remember we have what's called the spinal olivary tract. Information is coming from proprioceptors to the spinal cord. crosses over, comes up to the inferior olives, and the inferior olives crosses over to the opposite cerebellum. The olives, when it sends these axons into the cerebellum, it sends it into the cerebellum, we'll talk about particularly what area it's going to go into. It's going to be the inferior cerebellar peduncles. But when we get into this, what you'll see is, as these fibers come in, they give off axons that go directly to the deep cerebellar nuclei. It can give off axons that go directly to the deep cerebellar nuclei. But important is it actually can ascend. So it ascends up, ascends up, ascends up through the granular layer into the molecular layer. In the molecular, I'm sorry, the Purkinje layer. In the Purkinje layer, it gives off these axons. And these axons are going to act on the Purkinje fibers. So we have two different areas. One area is it gives off axons to go to the deep cerebellar nuclei. And another one is it gives it off to go to the Purkinje. cells. How does this work? Well, once it comes in, it releases a specific neurotransmitter. This is going to be a spartate. And a spartate is a stimulatory neurotransmitter that will stimulate the deep cerebellar nuclei. The deep cerebellar nuclei upon stimulation will then send out axons to go to different areas. Maybe it's going to go to the vestibular nuclei. Maybe it's going to go to the... reticular formation, maybe it's going to go to the olives, maybe it's going to go to the cerebrum, we don't know. We'll get into that, but all we know is that it's going to stimulate it and it's going to send out a potential, or an action potential. It also can give these axons that go all the way up here to the Purkinje cells. And again, what do we say it releases? Aspartate. Aspartate, we said, is a stimulatory neurotransmitter that can stimulate these Purkinje fibers. Here's the interesting thing. When the Purkinje fibers are stimulated by these fibers, and we're going to give them a specific name, a very particular name, it activates the Purkinje fibers. They send down action potentials, but here is the interesting part. These Purkinje fibers, they release inhibitory neurotransmitters, and these inhibitory neurotransmitters is particularly going to be GABA. So this is going to release GABA. which if you know that stands for gamma amino butyric acid. And then these ones here are going to release aspartate. So we'll put ASP here. Okay, so GABA here, which is an inhibitory neurotransmitter, and then aspartate, which is a stimulatory neurotransmitter. Now here's what's interesting. We said it comes in, stimulates the deep cerebellar nuclei that sends out the action potential to activate other structures in the brainstem. But then it comes up here, activates the Purkinje fibers, and the Purkinje fibers are inhibited. Again, it's to control the overshooting and the undershooting of whatever movement that we're trying to coordinate. We don't want it to be too excessive and we don't want it to be not enough. So it's important for neural sharpening. Now, here's the important name for these fibers. These are really important because one thing I need you to remember is that one fiber goes for one Purkinje. One fiber can go to this one Purkinje. This is going to be called... your climbing fibers. So these fibers here are called your climbing fibers. And the climbing fibers again to remember this one is it is going to be connecting from the inferior olive sending in the information to the deep cerebellar nuclei where it will stimulate it continue to go up to the Purkinje's fibers activate them but they and release GABA that inhibits this deep cerebellar nuclei to play a role with a neural sharpening. That was an easy one. The next one is a little bit harder. We have other fibers. Let's do these ones in blue. This next one is going to be what we call mossy fibers. Now here's the thing, mossy fibers come from every other sensory pathway. So every other sensory pathway that you can think of, so watch this, comes in, let's use a different blue. So again we have these mossy fibers, that's better. These are going to come in. And what they're going to do is they're going to give off axons that go to the deep cerebellar nuclei. The deep cerebellar nuclei are going to get stimulated because guess what this guy releases? He releases glutamate. Glutamate is a stimulatory neurotransmitter. Activates the deep cerebellar nuclei. The deep cerebellar nuclei sends axons out to control whatever nuclei in the brain stem, which plays a role in the neural sharpening, as well as, again, what? Maintaining posture, maintaining balance, maintaining equilibrium, maintaining the coordination of the movement and motor learning. Now. These are going to be coming from multiple different structures. We'll go over these in more detail when we get into the pathways. But what I want you to remember is that this is coming from the sensory pathways. We're just going to put that for right now so that we don't go overboard in this area. We're just going to say sensory pathways. These sensory pathways are going to be coming in and what they're going to do is they're going to give off these axons to the deep cerebellar nuclei. And again, what do we call these fibers? These are called Mossy fibers. Mossy fibers will give off this stimulus. Activate this, but here's where it gets a little interesting. It comes up to the granular layer. In the granular layer, it gives off its axons that go and connect with the specific cells in this area. What do we call this area? The granular area, the granular layer. What do you think those cells are? They're granule cells. So these cells right here are called granule cells. Granule cells. So what happens is these mossy fibers give off multiple axons. Multiple axons to these granule cells. It also gives some axons off to this little weird looking cell over here. And this is called a Golgi cell. So what is this cell here called? We're going to write in pink. This is called a Golgi cell. So we'll write this one here. This is a Golgi cell. These are both in the granular layer. Okay? So what happens is these monocular fibers come up, give off stimulus to the deep cerebellar nuclei, continue to go up, relieve off multiple axons onto these granule cells, and give off axons to the Golgi cells. They have a name for this structure right here. I'm going to kind of highlight it like this. This like... tuft of interaction here where you have multiple granule cells and axons of the mossy fibers connecting this is called a glomeruli now again what do we say these fibers are releasing what kind of neurotransmitter glutamate that's a stimulatory neurotransmitter so when it releases the glutamate the glutamate should stimulate two cells the granule cells which will send axons upwards and stimulate the Golgi cells. We'll get to the Golgi cells in just a second, okay? But we'll come back to it, okay? Mossy fibers come up, activate these guys, stimulate the granule cells, and they start becoming stimulated and send axons upwards. Now, as these granule cells ascend upwards, their axons come upwards, they move through the Purkinje layer into the molecular layer, and then they spread out. They make like a T formation, these parallel fibers. So it comes up, boop, boop, and this one come up, boop. And it's going to cause all these parallel fibers to move all the way across the molecular layer. Now here's the cool thing about these. These fibers, once they're in this area, they can act on a couple different structures. They have these two important cells in this area. This bluish one is called a stellate cell. So this is called a stellate cell. And then this one over here, this green one, is going to be called a basket cell. Now, what happens is these granule cells, when they give their axons, they come up here and they can stimulate three important structures. They can give off axons that go to the stellate cells, and they can give off axons that go to the basket cells. Now, what did we say? Once these are activated, they're going to come up and they're going to give these axons to the basket cells. Whenever they release these neurotransmitters into the basket cells, it actually stimulates these basket cells. So it'll release a stimulatory neurotransmitter that activates the basket cell or can activate the stellate cell. Whenever these are activated... activated, these stellate cells and basket cells release inhibitory neurotransmitters. Okay? They release inhibitory neurotransmitters, and these inhibitory neurotransmitters are then going to inhibit. the Purkinje fibers, okay, the Purkinje cells. But before that happens, remember we said these granule cells, they send up their parallel fibers into the molecular layer, activate the stellate cells and the basket cells, but guess what else they do? They give off axons directly to the Purkinje fibers. So now let's show that. So it gives off axons here to the Purkinje fibers. When it gives off these axons to the Purkinje fibers, it actually stimulates the Purkinje fibers. So what you get is you get stimulus to the Purkinje fibers that then can go down and release inhibitory neurotransmitters here. All right, so the mossy fibers are a little bit of a harder pathway. So let's get this down to like a simple way, right? Because I know it's a lot. Sensory pathways come in. Remember, this is a bunch of different sensory pathways. First thing, stimulates the deep cerebellar nuclei. Second thing, comes up, activates multiple granule cells and Golgi cells. The granule cells send up their axons into the molecular layer. First thing it can do is stimulate the Purkinje fibers. The Purkinje fibers can send down axons and inhibit the deep cerebellar nuclei. Also, to play a role with the neural sharpening, these parallel fibers can also give off axons to the stellate cells and the basket cells. It can stimulate them. When they're stimulated, they inhibit the Purkinje fibers. When they inhibit the Purkinje fibers, the Purkinje fibers are now no longer going to be releasing GABA. So the deep cerebellar nuclei in that area will fire. This is helping to make sure that in certain areas of the cerebellum, we're having those axons fire, and in certain areas, we're not. Again, it's playing a role with that overall goal here, neural sharpening. Now, another thing here, as I mentioned, is that these mossy fibers, whenever they act on the granule cells, they also give off fibers to the Golgi cells. When the Golgi cells are stimulated, guess what they do to the granule cells? They inhibit them. So they can also play a role in inhibiting the granule cells. And again, it's playing a role within all that modification, that neural sharpening activity. Again, guess what else can happen? Not just these mossy fibers can stimulate the Golgi cells, but whenever there's a lot of activity running through these granule cells, the granule cells can also stimulate the Golgi cells. And guess what the Golgi cells can do? They can inhibit the granule cells. So there's this constant control in this. feedback in this intense circuitry here when it comes to the mossy fiber path. Okay? So that is how we would describe our internal circuitry. What we're gonna do now is, and I know it was a lot, is we're gonna go ahead and we're gonna take a look at some of the pathways associated with the cerebellum. Alright, so let's finish up here guys talking about the pathways. So if you remember, go back to that first diagram we said talking about appropriate receptors connecting with the cerebellum. how the vestibule and the semicircular canals are connected to the cerebellum, how the cerebellum is also receiving information from the cerebrum, how it's sending that information out up to the cerebral cortex, and how it actually sends information to some of the nuclei within our brainstem that controls our extra-parameter pathways. We're not going to go into all the pathways. The reason why is, is this, it'll look like a crime scene if we do that here. So, if you guys want to know a little bit more about some of the pathways, So our specifically the pyramidal tracts, like our corticospinal tracts, our subcortical tracts. If you want to learn about all the ascending tracts, go into our neurology playlist and watch some of those. The reason why is I just want us to focus more on the cerebellum at hand than going into all of those tracts, okay? So how we're going to do this is we're going to go through the connections, the pathways, and basic detail here with respect to the peduncles. I think it's an easier way to celebrate them. them, not celebrate them, separate them. Okay? So what we'll do first is we'll start with the superior cerebellar peduncles and we'll talk about the relationships there with this one. Okay, superior cerebellar peduncles. Here's what I want you to remember for this one. It has afferent connections and efferent connections. So afferent and efferent connections. So what do I mean? So the first one we're going to go with is we're going to talk about the efferent connections. So efferent connections, meaning that the fibers coming from those deep cerebellar nuclei are going to go directly to a specific structure. They're coming out of the cerebellum. So that's what efferent means. Those deep cerebellar nuclei that we were talking about over there, that big green one coming out, it's going to go to specific nuclei out here in the brainstem or the thalamus. We'll talk about what I mean by that. Afferent pathways is we're going to talk about fibers like the mossy fibers or we're going to talk about the climbing fibers. So all of this should start coming and making sense what we're trying to do here. Efferent, what are the important processes here with respect to the efferent pathways in the superior cerebellar peduncles? Okay, so let me put this up here really quick here. Let's write over here that this is specifically SCP, superior cerebellar peduncles, is what we're talking about with this one. Now, efferent, what's coming out? The first one that I want you to remember is the dentate nucleus. If you remember we had the dentate nucleus. I'm just going to do it here in pink for this situation. But we're going to put here the dentate nucleus. The dentate nucleus is a part of the cerebrocerebellum. Remember that? The cerebrocerebellum, the lateral hemispheres. Whenever it receives signals via the afferent pathways coming from the cortex, what it'll do is it can has two main pathways. It can send its axons out to two areas. One is it can send it to the red nucleus in the midbrain. Another area is it can send it all the way up here to the thalamus. So it can send it to the red nucleus and it can send it to the thalamus. Now here's what I got to be careful of. It goes to the contralateral side. So when I do this one, I want to show you this. I got to be particular. It actually goes to the contralateral thalamus. or the contralateral red nucleus. So the dentate nucleus, let's put that here, dentate, if we want to talk about its etherent pathways, it can send axons to the contralateral red nucleus or it can send it to the contralateral thalamus. Sometimes it can even connect from the red nucleus to the thalamus. So there can even be axons here that can go from the red nucleus to the thalamus. What is this pathway called? So we have two different pathways. One is if we go dentate directly to the thalamus. This is called dentothalamic pathway. Now, what's the significance of that? It's simple. Remember the cerebrum was sending information down to the cerebellum about what it wants to do? The dentate nucleus says, okay, I've done everything. I've received proprioceptive information, vestibular information, information from what you want to do. What I'm going to do is I'm going to send my perfect, corrected, organized, calculated plan back to you. Guess how it does it? It sends it from the dentate nucleus to the thalamus. Guess where the thalamus can send information? To the cortex. So now from here, it's going to send this information to the primary somatosensory cortex, to the primary motor cortex, to the premotor cortex, to the supplementary motor area. And now it has the perfect motor plan. Isn't that beautiful? Now, next thing it can do is it can activate the red nucleus. Now, the red nucleus can go up to the thalamus. That's just a modified pathway. So we call that the dentorubrothalamic pathway. And it's the same concept here. Same concept. Okay? Same concept. I'm going to send the information to the red nucleus, go to the thalamus, and up. What can happen is the red nucleus can also get activated. If the red nucleus is activated, if you go back to our extrapyramidal pathways, what does it do? The rubrospinal pathway. So if the red nucleus is stimulated, it can cross over. It moves to the contralateral side. That's important. I can't stress that enough. That's important. What will happen is, if it's stimulated, this can... cross over to the contralateral side and move down into the aspect of the spinal cord and activate lower motor neurons that go to our flexor muscles, particularly of the distal extremities. That's called the rubrospinal pathway. So again, two efferent pathways I want you to remember is dentate to thalamus, dentate to the red nucleus to the thalamus, but again another pathway with this is you can also have the rubro. spinal pathway. Okay. Another thing is it just doesn't have to be the dentate nucleus that receives information. This is also pretty cool. It can also receive information from the globose and emboli form. Let's do that over here now. So let's put here we're gonna have the globose and we'll have the emboli form. So we have emboli form and then over here We'll have the globose, again collectively we call these the interposed nucleus. We're going to do one specific color here, but they can send out axons and these axons can go again to the Contralateral red nucleus. If it activates the contralateral red nucleus, what does the red nucleus do? Decocetes. Goes down to the other side of the spinal cord, activates the lower motor neurons, and then goes out to the muscles. Right? So that should be a simple concept there. So that's another pathway is you can also have the interposed nucleus go to the red nucleus. Okay? Another pathway that can happen, it's common in both areas, is you also have another one which is called the cerebellovascular vestibular pathway. Okay, let's write this one down here. Cerebellum vestibular pathway. So what happens here is, this one is actually extremely weird. It's kind of interesting, this one. Here's our vestibular nuclei located in the medulla, right? Our vestibular nuclei, superior, lateral, medial, and inferior nuclei. Remember we had those Purkinje fibers? Those Purkinje cells. It's weird because it used to be thought that the vestigial nucleus was the connection. The deep cerebellar nuclei that connected to the vestibular nuclei. Now, they're finding that the Purkinje fibers actually directly leave. They don't even go to the deep cerebellar nuclei. They actually come out and they are the ones that directly stimulate the vestibular nuclei. If the vestibular nuclei are activated, go back to the vestibular pathway. What can the vestibular nuclei do? They can activate the vestibulospinal tract. It can go down through the spinal cord, activate the lower motor neurons, and go to muscles. Which muscles? Extensor muscles, anti-gravity muscles, and here's the other one I want you to remember. If it stimulates it, guess what else it could do? It can go up and do what? It can activate. What's this structure here called? Medial longitudinal fasciculus. The medial longitudinal fasciculus is connecting what particular structures? The third cranial nuclei, the third cranial nerve, the fourth cranial nerve, and the sixth cranial nerve. What is that specifically responsible for? The extraocular movements. So, what I want you to remember is, efferent pathways, dentothalamic. Dentorubrothalamic controlling the interaction with the cerebrum letting it know the premotor plan or the motor plan that it calculated Cerebellar vestibular tract is connecting via the Purkinje fibers directly to the vestibular nuclei What are the vestibular nuclei do they go vestibular spinal tract or they can go up via the medial longitudinal fasciculus which controls your extra ocular movements again. This is your Purkinje, okay? Okay, next thing, we'll go to the afferents. Afferents, again, we're not going to go through all of the pathways here with the afferents because we've already gone over that in our cerebellar video, the ascending tracts of the cerebellum. But for this one, I want you to remember just three important ones. So one is going to be the, we talked about this in the cerebellar video, the ventral spinocerebellar tract. Okay? And if you remember the ventral spinal cerebellar tract, we're not going to go into all the detail, we did it in that video. It takes sensory information from proprioceptors below what level? L2, L3. So it's usually, we'll put it here, we'll put below L2, L3 level. Okay? That's an important one. The other one we did not talk about, but again, it's still an important one, is called the rostrocerebellar tract. So we're going to put this one here. The rostro... Sarah Beller. tract. This one is taking it from the cervical region. So from the cervical region of the spinal cord. Okay so cervical and even upper extremity region of the spinal cord. And that one is also going to the superior cerebellar peduncles. And the last one is going to be the tectocerebellar tract. So the other one is going to be the tectocerebellar tract. Now if you guys know what the tectum is, tectum is actually the superior colliculus and the inferior colliculus. We're going to represent it with this brown little color here. The tectum receives information from our visual. Superior colliculus is visual stimulus. And then the inferior colliculus is going to be auditory stimulus. That can send information also to the cerebellum to make sure that it helps us to coordinate our eye movements and our head movements in response to visual or auditory stimulus. Isn't that a beautiful thing? So again, let's put that in here. We also have the tecto. Cerebellar tract here. Okay? So that's an important one. So, atherin pathways that are going into the superior cerebellar peduncles is going to be the ventral spinocerebellar. If you remember, proprioceptive information from L2, L3 below. If you want to remember, comes in, crosses over, comes up, and then does what? Goes to the superior cerebellar peduncles and then crosses over to the opposite side. Remember that? It's interesting. Rostral cerebellar, just remember that it's coming in and it's also going to go through the around the dorsal column area up and then it's going to be taking information from the cervical and upper extremity areas. Tectocerebellar coming via the superior colliculus, inferior colliculus, sending that information based upon visual and auditory stimulus. These are the main ones that I want you to remember for the superior cerebellar peduncles. Okay, next one we're going to go to is we're going to go to the middle cerebellar peduncles. We're going to do this one right here. So this one is going to be for the middle cerebellar peduncles. So MCP. Now I want to mention something just because some people usually, some people don't understand it completely, but peduncles. These peduncles, they're not little tubes, they're actually the axons of these fibers going in and out of the cerebellum. So that's really what's making up these peduncles. So if you understand the peduncles, like what those actually are, it'll help you to really understand the connections with the cerebellum. Okay, middle cerebellar peduncles. Don't know why I have two here. It's one main thing, really important, the most thick, biggest peduncle of all of them. This one is particular. We're going to do it here in orange because that's where we're going to have these nuclei. Is this going to be related afferent? It's going to be primarily afferent, actually not primarily, all afferent. Okay, what is this connection? It is via what's called the cortico. It's a heck of a name. Ponto. Cerebellar fibers. Okay, this is a really, really, really important one. Remember I told you back in the general way, the primary somatosensory, the premotor, the primary motor, the somatosensory cortex, all those areas of supplementary motor, they're developing a motor plan. That motor plan, what are they doing? They're sending it down to the lower motor neuron, but also what else do they do? Remember I told you, we'll do it here in this color. It's sending this motor plan down. Let's just say this is one of those areas of the motor cortex or the somatosensory cortex. It's coming down and it comes to these pontine nuclei. So here's the upper motor neuron. And then this area right here where it's synapsing is our pontine nuclei. Same thing over here. If I were to draw this one, this would be coming down and this would be going to our pontine nuclei. So upper motor neurons. to the pontine nuclei. So that's where we have corticoponto. From here, these axons cross over, and this will come here, and then these will come over here. And isn't that insane? All of these fibers pass through here and then go to the cerebellum. Now, what is that designed to do? The cortex is coordinated with what other structure? We can't forget this. What other structure is it coordinated with up here in the cerebrum? These are two intricate structures. One is going to be the basal ganglia. So it's also coordinating with the basal ganglia. Sending the information down, motor plant goes to the pontine nuclei. Pontine nuclei cross over to the other cerebellar cortex. Cerebellar cortex receives this information. As well as the proprioceptive information, as well as the inner ear information says, okay, developed a perfect plan. Guess who it sends it back up through? Dentate to thalamus to the cortex. Or it can go dentorubrothalamic pathway. Isn't that interesting? And it tells it, okay, I received everything. I've calculated the perfect plan for you. So that one's an interesting one. I love that one. Okay, the last one is the inferior cerebellar peduncles. So let's put this one here. This is going to be for ICP. ICP. Inferior cerebellar peduncles. This is a little bit of a bigger one. Okay, we're going to go through afferent first because it's primarily afferent, but we'll talk about a couple efferent ones. Okay. So the afferent ones. The big one is remember we said for the SCP it was ventral spinocerebellar tract. I want you to remember dorsal spinocerebellar tract for the afferent. So for this one I want you to remember dorsal spinocerebellar tract. Remember that one comes in, when it comes in it actually synapses on the Neurons of the posterior grey horn goes into the same side of the lateral white column, ascends upwards and goes to the same cerebellum. The other one, and then what is this L level? This is from C8 to L2, L3 area. Some books will even say T1. But this is where the Clark's nucleus is. The next one is the cuneocerebellar tract. Remember, this one comes in. goes to the dorsal gray horn, actually goes into the dorsal gray horn, ascends up, goes to the accessory cuneate nucleus, right? And then that goes in via the external arcuate fibers into the cerebellum. That's going to be the cuneal cerebellar, and this is picking it up from the cervical region. So above C8. The next one is it's going to be receiving information from the vestibulocerebellar tract. The olivo cerebellar tract and the reticulo cerebellar tract. Now let me work through this one, okay? Vestibulocerebellar tract, where is that receiving information from? The inner ear. So let's write that over here. Let's put the inner ears right here. We're not going to draw the whole structure here. I just want to write inner ear. Over here, inner. Here, these come in, right? They go to the vestibular nuclei. From the vestibular nuclei, where can these go? They can send their axons in about the balance and equilibrium into the inferior cerebellar peduncles. And then again here, and then boom. Another interesting thing is, there's actually been research that shows that the fibers from the vestibular cochlear nerve can actually go directly in to the actual cerebellum. Olivocerebellar. Remember we have the inferior olives. The inferior olives, if you remember, we have the spinal olivary tract, receives information from the proprioceptors, comes into the dorsal gray horn, crosses over, ascends, goes to the inferior olives, and then the inferior olives, they cross over and go to the other side of the cerebellum. So these are also important ones, and they're going to be receiving information, and they're going to be sending the information to the contralateral one, but it's going to be on the ipsilateral side. So what I mean is, Just to reiterate here, I know that we have a video on it, but let's say that you have the proprioceptors here, sends it in, synapses, crosses over, ascends, goes to this inferior olive, and then this inferior olive will cross over and go to this side, okay? Everything for the cerebellum should be ipsilateral. That's why whenever you see people who have ipsilateral cerebellar ataxia or some cerebellar disease, Whether it be due to multiple sclerosis or B12 deficiency, whether it be due to alcoholism, whether it be due to a cerebellar infarct, whatever it might be, whenever they have that ataxia, it's on the ipsilateral side. Okay, that's important because of all the connections are ipsilateral. Next thing, vestibular cerebellar connects with the inner ear. Olivocerebellar connects with the inferior olives, which is taking information proprioceptors, right? And this is the important one. What is this pathway coming in from the inferior olives? The climbing fibers, these are super, super sensitive because remember they interact directly with what neurons? Purkinje. And the last one is the reticulocerebellar. And the reticulocerebellar is important because it's receiving information about all of our sensory information throughout the entire body. And it's going to be taking that and sending that into the cerebellum, letting it know of what's going on in the body. Okay? Efferent. Efferent, the ones that I want you to remember here, is going to be... The cerebellum, so we'll say here, let's actually keep it in green here, cerebellum reticular, cerebellum reticular, and cerebellum vestibular. And some books and some literature will even say cerebellum olivary, but there wasn't a lot of research on that, so I don't want to include that one, okay? So cerebellum reticular, it's simple. You have, we'll go back to this one, cerebellar reticular, fastigial nucleus. The fastigial nucleus actually connects with the reticular formation. When it connects with the reticular formation, go back to those subcortical tracts. What were the two tracts from the reticular formation? The medullary and pontine. Medullary is going to be for what? Flexion. Pontine is going to be for extension. Now, if they're activated, they send down those axons through the spinal cord and go and activate those particular muscles. Cerebellar vestibular, it's going to send information from the Purkinje fibers. Purkinje fibers go directly to the vestibular nuclei. They can go up via the medial longitudinal fasciculus to control extraocular eye movements or they can go down via the vestibular spinal tract and activate the extensor muscles or anti-gravity or postural muscles. Alright Ninja Nerds, I hope you guys like this video. I hope it made sense. I really do. If it was hard, just continue to keep working at it. It'll come with time. This is just a lot of practice. If you guys like this video, just please hit that like button, subscribe, leave some comments down in the comment section if you guys can. Go check out our Facebook, our Instagram so we can keep in contact with you guys. Also, if you guys have the opportunity, if you could go and donate to our GoFundMe page or our Patreon, we'll have those down in the description box. We truly appreciate that. I just want to say thank you, Ninja Nerds, for everything that you guys do. We love you and until next time. Thank you.

We'll cover the anatomy, but this is going to be more for the functional anatomy. Then what we'll do is we'll take a slice of the cerebellum and look at the internal circuitry of it, specifically the deep cerebellar nuclei, and then we'll go into a lot of the pathways associated with that. So first thing, just in general, cerebellum, it sits within the posterior cranial fossa of the skull.

Remember that, anatomy-wise. It's separated from the cerebrum by a dural septa called the tentorium cerebelli. Another important thing about the cerebellum, is when you look at it, you're going to notice that it has these things called folia. Folia are just kind of like little folds. That's basically what they are.

And what they are designed to do is to increase the surface area of the cerebellum. So if you notice here, I kind of made this like squiggly dark line there. That is particularly, that's pertaining to the outer gray matter of the cerebellum.

The gray matter, you guys should know, is unmyelinated cell bodies or dendrites. In the center of this actual cerebellum, we have what's called the tree of life or the arborvitae. This is important because it contains the myelinated axons of multiple fibers that are connecting the cerebellum to the brainstem, to and fro.

All right, so it can be from the brainstem, from the cerebrum, from the spinal cord, from the inner ear. We'll talk about all these pathways, which is extremely interesting. And then again, we'll talk about some of the deep cerebellar nuclei associated here. First things first, we have the two particular fissures which separate the cerebellum into their structural lobes.

So the first one we're going to do like right here. We'll do that one. That's called the primary fissure.

We have another one which is right here and that is going to be the posterior lateral fissure. Okay so we have these two fissures here primary fissure and posterior lateral fissure. Same thing we'll talk about it over here and we'll highlight that.

What I want to do is we have three lobes that are anatomically separated from one another. We're going to do this first one right here, this green. This is going to be a particular lobe, more of a primitive area of the cerebellum, and they call this area the flocculonodular lobe. Okay, we'll talk about its functional name whenever we get to this diagram.

Another lobe is going to be here. This is a really, really big one and this is called the posterior lobe and this is more of the newer more modern part of the cerebellum. We'll talk about its functional name in a little bit. And then we have this other one up here and this is going to be the anterior lobe.

And again we'll talk about its functional term here as well. So we know the outer gray matter, we know the white matter, the arborvitae, we have the folia separated by the dentorium cerebelli, little brain, right? And we know that we have these primary fissure, posterior lateral fissure. anterior, posterior, and flocculonodular lobe.

The next thing we need to understand about the cerebellum is just the basic thing that I want to get us started with because it's going to help us throughout the process of this entire video is what is its functions. I want you to remember, there's a bunch of them, but I want you to remember specifically the first one is balance and equilibrium. Okay, so we'll kind of put these separately.

Balance, equilibrium. Now, where does that come from? We're not going to go into a ton of detail because we'll go into that a little bit later, so I'll save it for that.

But what I want you to remember is this is connecting. The cerebellum is connected with the inner ear. So what we're going to do is we're just going to say here's our inner ear for right now.

We're not going to go over the semicircular canals and all that stuff like that. But the inner ear is connected to the cerebellum. And we'll talk about the actual vestibular cerebellar tract.

But the inner ear is carrying with it balance and equilibrium from the semicircular canals, right, which has the crista ampullaris and the vestibule which consists of the macula. Okay, the next thing that it plays an important role is for muscle tone. So it plays a role within our muscle tone. So let's write that down.

So muscle tone and it also plays a role in the coordination of our movement. So muscle tone and coordination. And it plays a really, really important role in motor learning.

So what do I mean here? I'll explain. So I want you to remember this. Balance and equilibrium, muscle tone, coordination, motor learning. These are the really important things that are controlled by the cerebellum.

We know the inner ear is respect to the balance and the equilibrium. Okay? The muscle tone is particularly through specific pathways, spinal pathways. So if you guys remember, we've gone through a lot of these. This is going to be from your proprioceptors.

Proprio. receptors. Your Golgi tendon organs, your muscle spindles, your joint capsules, all of those structures they're picking up proprioceptive information if you don't know what proprioception means.

Your position of your muscles, your joints, your tendons, your ligaments, all of those in a three-dimensional space. Your awareness of where you are. It takes that information and sends it to the cerebellar cortex.

The cerebellar cortex receive information from your inner ear, your proprioceptors and here's another important thing. It also receives information about the motor plan. What kind of movement your cerebral cortex is going to execute.

So you have some specific areas here. If I were to kind of highlight here, we're not going to go into crazy detail, but remember you have your central sulcus. What's some of the big areas here around the central sulcus? Let's do this in this color here.

Remember here behind it you have the Primary somatosensory cortex. In front of it you have the primary motor cortex. You have the supplementary motor area. You have the premotor cortex.

All of these areas are associated with the actual motor planning, specifically sending down descending axons. These are your upper motor neurons. They'll send fibers down where? Look, let's say that we just take it from any of these.

Here's your upper motor neuron. It'll come down. Go to an area of the spinal cord to the ventral, the anterior gray horn, activate a lower motor neuron which will go out to what?

To a muscle, right? Let's draw here our muscle. Go out to a muscle, right? So we know that the cerebral cortex is responsible for sending down these upper motor neurons down to a lower motor neuron, activating a muscle to cause it to contract. While it's sending these pathways down, guess what it's doing?

It's letting the cerebellar cortex know of these things. So it's saying, hey, cerebellum, I have some motor plans that I want to coordinate. I want you to be aware of that.

So now the cerebellum is receiving information from the inner ear about balance, equilibrium. It's receiving information about our proprioceptors all throughout our entire body. It's receiving a pre-programmed motor plan, which has already gone through another structure, not just the cerebral cortex, but the basal ganglia. And it's sending this information down to the cerebellum. He's going to coordinate that.

He's going to develop a perfect, perfect calculated plan and a blueprint. And then from there, it's going to say, okay, I think we have the perfect thing. What I'm going to do is I'm going to let you know what I think you should do.

And we'll talk about all these pathways. This is just a general overview of what we're going to talk about, okay? So we have an idea here of what the cerebellum's anatomy is.

We have a basic idea of its function. Let's go ahead and let's get into a little bit more detail on the functional anatomy of the cerebellum. What we're going to do is, I'm going to take the cerebellum and I'm going to unfold it. And I'm going to look at it in a posterior view. So this is going to be a posterior view.

And we're going to cover the, again, the anatomical components here. But what I want to do now is I want to kind of start switching over into more of a functional anatomy. So again. To give you guys an idea, remember we said that the anterior, so this is going to be anterior lobe, posterior lobe, flocculonodular lobe. All I'm doing is I'm just unfolding it.

Okay, so here, let's write these down. The three lobes, we're going to coordinate it with the colors. So this top lobe up here, which is this top lobe, that's going to be, so again, coordinating this, anterior lobe, anterior lobe.

We'll write this one up here. So anterior lobe. Okay.

Next thing, this bottom one down here is this one right here. That's the posterior lobe. So we'll have that in this purple color.

And then this last one down here, which is tucked into this little area here, this green, that's our flocculonodular lobe. Such an interesting one. That is the flocculonodular. Nodular lobe.

So, flocculonodular lobe. You know the flocculonodular lobe is actually one of the most primitive of all of them. It's also referred to, and we'll talk about it in a second, called the vestibulocerebellum.

Also called the archicerebellum. It's a very, very primitive area of the cerebellum. Okay. So, we have the coordinating lobes. And again, I told you I was going to mention those fissures, so I don't want to forget about those.

This fissure here, which is separating that one right there. Again, same thing. This is particularly the . Primary fissure, so primary fissure.

Separating the anterior lobe from the posterior lobe. And then remember this one right here is going to be the posterior lateral fissure, separating the posterior lobe from the flocculonodule lobe. So posterior lateral fissure. Okay, good deal. Now that we've gotten the idea of our anatomical lobes, we want to look at them in a different way.

Now we're going to look at it in a functional area, functional zones. So we have three different functional zones coordinating respectively with the corresponding lobes. Here's the first thing. The anterior lobe is also called the spinocerebellum. So let's write this down.

So when we talk about the anterior lobe, another specific one for this functionally is called the spinocerebellum. Now. When we talk about the spinocerebellum, here's the tricky thing though. It is particularly occupying what's called the vermal zone.

So you know when you're looking at the overall anatomy of the cerebellum, you have the lateral hemispheres and then you have the vermis. The vermal area, this is your vermis right here, the central piece right here. The vermis is primarily going to be a part of the spinocerebellum.

So what I'm going to do here is we'll have this part here. is going to be a part of the spinocerebellum. It also has some nuclei here that we'll talk about in a second when we get there.

Going on the sides of that, what I'm going to do is I'm going to kind of make like a little dotted line here. We have another area which is important for the spinocerebellum. And this is on the sides of the vermis.

So what does it mean when it's on the sides? So this is the vermal zone. This area over here is the paravermal zone. We also give it another name which is the intermediate zone.

So when I talk about the spinal cerebellum, I want you to remember three components of this. It occupies the vermal area and the paravermal area. Another name for the paravermal area is the intermediate zone.

Now here's the important thing with this. What I say spinal cerebellum does, it picks up sensory information. So don't, like in the cerebrum, don't we have a sensory homunculus?

Guess what? We got a homunculus for the cerebellum. So, how does this generally work? Well, what we do is we're going to look at it from up in this top lobe and then this bottom lobe.

Okay? There's this kind of sensory homunculus, and here's how it kind of goes. Don't laugh because it does look funny. It looks like a little alien.

But in general, we start off here. In the vermis, it's mainly for the axial part of our skeleton, our axial musculature. So what you'll see is you'll see the trunk.

You'll see the neck and you'll see the head. But the head kind of also spreads out and kind of splurges over into this paravermal area as well. More of the temporal parts here.

And here, let's put a little smiley face for the guy, a little bit of hair, right? So, if you look here, the trunk, the neck, and aspects of the head is occupying the vermal zone. So, the vermal area is primarily getting sensory information from the trunk, the neck, and the head.

The extremities, let's put here, here's his lower leg, here's his other lower leg, here's his upper extremity, and here's another upper extremity. This is going into the paravermal area. So the paravermal area of the anterior lobe is particularly taking sensory information from the upper and lower extremities and certain aspects of the lateral head.

Now, the next thing is for this bottom part down here in the posterior lobe. There's another aspect, there's another sensory homunculus. But this sensory homunculus is kind of odd. How it works is you have two little homunculi back to back with one another.

So now what I'm going to do is I'm going to have the head here, I have the little nose, here's like a little face. We'll have another one here. And then here's going to be their trunks, here's his trunk. And then coming out here is going to be this arm, this arm.

This leg, this leg, this arm, this arm, this leg, and this leg. This is going to be the sensory homunculus for this bottom part, for this vermal and paravermal zone within the posterior lobe. Okay? So when we're looking at the sensory homunculus, it is really important just to understand that within the vermal area is going to be the trunk, neck, and the head.

And then for the paravermal or intermediate zone, it's going to be for the upper and lower extremities. Okay? Boom. We beat that like a dead horse.

Now, we go to the next part, posterior lobe. Posterior lobe is mainly going to be occupying this functionally. Functionally is going to be this area over here.

So now, just take all of this and just highlight this. This is going to be the lateral hemispheres. So this is primarily, the posterior lobe is going to occupy the lateral hemispheres.

So let's write this down here, lateral hemispheres. So this is the functional. areas of it.

And we'll talk about a really, really important nucleus in this area called the dentate nucleus. Mmm, it's going to be good. All right, next one. We go to the flocculonodular lobe.

That's this little guy. We unfolded him. Remember, it's separated to be the posterolateral fissure. Well, you have this area here, so you have the nodulus, and then you got your flocculus over here, these little flocculus.

This is important because it's believed to be important with respect to the vestibulocerebellum. So they believe that this is particularly related to what's called the vestibulocerebellum. So, vestibulocerebellum.

And this is going to be picking up information from your vestibular system. Now, I forgot to mention here with the posterior lobe. Remember we said vestibulocerebellum for the flocculonodular lobe.

Spinalcerebellum for the anterior lobe. Another really important one that we got to mention here for this posterior lobe is this is going to be what's called the cerebrocerebellum. And this is going to be connecting the cerebrum to the cerebellum.

Now, let's make sense of all this really quick before we move on. Spinal cerebellum, it's this proprioceptive pathway, right? That's all it is. And it's taking it from the proprioceptors of our trunk and our extremities. Boom.

Going to the vermal, paravermal areas. Post-ear lobe, it's going to the lateral hemispheres. But where is it coming from? From the cerebrum. It's this motor plan going here.

Floculo nodular lobe, vestibular cerebellum. Where is it coming from? Inner ear. Isn't it cool to see how all of this stuff is kind of coordinated perfectly?

Okay, so we have an idea of the general anatomy. We have an idea of the functional anatomy as well as what these general things are responsible for. Now what I want to do is we've got to dig a little bit deeper, unfortunately. I'm going to take a slice of the cerebellum, and we're going to look into the cerebellum at some of the deep cerebellar nuclei. Okay?

Now, when we're looking at these, we're going to look at these from the lateral hemisphere. into the actual central part or the medial aspect here, right? I like to use a mnemonic to memorize these.

So I go by don't eat greasy food, okay? Don't eat greasy food. So how this works is don't eat greasy food.

The first nucleus here is going to be the dentate nucleus. Let's do this here with red. So the first one is going to be the dentate nucleus. And remember, which hemisphere did I say it should be associated with? The lateral hemisphere.

I want you to remember that. Lateral hemisphere. You'll see that this is a really important structure because it connects with the red nucleus and the thalamus. The next one is these two.

The bluish and purplish. So let's write these down. We're just going to do it in blue, but realize it's the same for both of these. Actually, I got an idea. We're going to call these the interposed, look at this, nucleus.

The interposed nucleus is made up of two components. Remember, don't eat. Eat, this blue one, is the emboliform nucleus.

So we have the emboliform nucleus. Don't eat greasy globos. So this is going to be your globus nucleus. The globus nucleus and the embolyform nucleus make up collectively what we call the interposed nucleus. Now, this is going to be primarily where?

The paravermal and vermal area. Makes so much sense, right? So again, this will be occupying the vermal and paravermal area.

Let's write that here, that this will be occupying the vermal. and paravermal area. Okay?

The last one is don't eat greasy food. This is for the fastigial nucleus. So this last one here is called the fastigial nucleus.

The fastigial nucleus is located in the center, but what I tell you... The flocculonodular lobe is responsible for the vestibulocerebellum. The vestigial nucleus is primarily connected with the flocculonodular lobe.

So I want you to write that one down. That one is associated with the flocculo. Nodular, this makes this a little bit nicer here for you guys.

Nodular lobe. Here's one more thing though. They've also found research. that it's not just in the flocculonodulo, but it also the fastigio nucleus is in the vermis.

So I don't want you to forget that one, but you can also write down on the side there it's also in the vermis. I'm going to put here, we'll put here on the side, plus vermis. Okay, so we have our structures here and I want you to remember the mnemonic. Again, how does this mnemonic go? Don't eat greasy.

food, don't eat greasy food. And this is your deep cerebellar nuclei, okay? So before we start going in now and looking at how these deep cerebellar nuclei connect with our pulmonary receptors, our inner ear, our cerebrum. I want to do a super quick recap.

Again, cerebellum, really important structure. What does it do? Balance, equilibrium, muscle tone, coordination, motor learning.

How does it do all this? Connects with your spinal pathways via appropriate receptors. Connects with our inner ear via the semicircular canal in the vestibule. Connects with our cortex based upon the pre-organized motor plan from these cortical areas. Takes all that, integrates it in coordination with the basal ganglia and sends it back up to the cortex with the perfect calculated motor plan.

If we take it, we have the primary fissure and the posterior lateral fissure. Anterior, posterior, flocculonodular lobe. Looking at it in the functional anatomy, the lateral hemispheres are going to be particularly for the posterior lobe, right? The cerebrocerebellum. The vermal and paravermal area is going to be for the spinocerebellum of the anterior lobe.

And the flocculonodral lobe is going to be specific for the vestibulocerebellum. If we dig in deeper and correlate the nuclei with these functional lobes, we have the dentate nucleus with the cerebrocerebellum, right? But specifically, the lateral hemispheres. The interposed nucleus, which is the...

Interposed nucleus is the globus and emboliform nucleus. These are going to be related with the spinocerebellum. And they are going to be...

taking into consideration the vermal and paravermal area. And the vestigial nucleus is the flocculonodulo, which is the vestibulocerebellum, which is connected with the inner ear structures. So now that we have a pretty good idea of that, what we got to do is we have to take and say, how does these nuclei interact with these fibers coming in or these fibers going out?

Okay, so let's go ahead and do that. Alright, so now we already said that we're going to dive into the internal circuitry. So to give you a little bit of an idea, just of what we have here, we separate the cerebellum, particularly the cerebellar cortex. Remember, what did I say?

The cerebellar cortex is consisting of what? Cell bodies and dendrites. Cell bodies and dendrites.

Now, remember I told you that there is some gray matter lodged in the center of the cerebellum. What were those called again? Deep cerebellar nuclei.

Don't remember the mnemonic? Don't eat greasy food. Dentate, emboliform, globus, fastigio. We're going to represent the deep cerebellar nuclei by one nuclei, but just realize that this could be for all of them.

It's not just for dentate. It's not just for any, like one specific one. It is for all of them.

This internal circuitry is for all of them. This green one is going to represent our deep cerebellar nuclei. What I'm going to do is I'm just going to put the save room because we're going to need it. I'm just going to put DC in.

And I want you to remember that that is our deep cerebellar nuclei. Then I told you that there's white matter, which is going to be connecting all the way up to the cortex, the cerebellar cortex. And here's what I want you to remember.

We said that the cerebellar cortex is cell bodies and dendrites. Look at all these. What we're going to do is we're going to separate this into three layers.

The subrheal cortex is three layers. Going from top to bottom. The first one that we have here.

is you're going to have the molecular layer. So this is going to be the molecular layer. And we're going to have two important cells in this area, and we're going to talk about them called the stellate cells and the basket cells. We're also going to have the parallel fibers of the granule cells too.

The next one is we're going to have the Purkinje layer. So this is our Purkinje layer. And then this one is nice and easy to remember because guess what? The Purkinje layer is consisting of the Purkinje. neurons, so the Purkinje cells.

And this last layer here, which is going to be the most inner layer, is going to be the granular layer. So this is the granular layer. So we got three layers of the cerebellar cortex from outer to inner.

Molecular, Purkinje, granular, and then if we go to the center of the actual cerebellum, we have the deep cerebellar nuclei. Dentate, embolyform, globose, and fastidio. Now, What we have to do is we have to see how if we have fibers coming in to the actual cerebellum, how it organizes all of these internal circuitries and determines which one is the most important signal.

Big thing I want you to take out of all this, because this is a lot. The big thing I need you guys to take out of all of this is that all of this internal circuitry is important for what's called neural sharpening. Okay? So it's extremely important with respect to what's called neural. Sharpening.

You're going to see a lot of things going on here. The neural sharpening is making sure that the most important stimulus is taken care of at that point in time. Okay, so we're trying to make sure that every signal that we send out of the cerebellum has the just perfect amount of Perfect plan for movement.

It's not going to be over amount. It's not going to be an under amount It's going to be just the right amount. So how does this work?

First thing we have to do is remember I said we have fibers coming in the cerebellum has fibers coming in through a couple different areas one important one that I want you to remember is from the inferior olives. So let's write that down over here. Let's do this one in this blue.

So we're gonna have inferior olives. I'm gonna put these right here, inferior olives. If you guys remember we have what's called the spinal olivary tract. Information is coming from proprioceptors to the spinal cord.

crosses over, comes up to the inferior olives, and the inferior olives crosses over to the opposite cerebellum. The olives, when it sends these axons into the cerebellum, it sends it into the cerebellum, we'll talk about particularly what area it's going to go into. It's going to be the inferior cerebellar peduncles. But when we get into this, what you'll see is, as these fibers come in, they give off axons that go directly to the deep cerebellar nuclei. It can give off axons that go directly to the deep cerebellar nuclei.

But important is it actually can ascend. So it ascends up, ascends up, ascends up through the granular layer into the molecular layer. In the molecular, I'm sorry, the Purkinje layer.

In the Purkinje layer, it gives off these axons. And these axons are going to act on the Purkinje fibers. So we have two different areas.

One area is it gives off axons to go to the deep cerebellar nuclei. And another one is it gives it off to go to the Purkinje. cells. How does this work? Well, once it comes in, it releases a specific neurotransmitter.

This is going to be a spartate. And a spartate is a stimulatory neurotransmitter that will stimulate the deep cerebellar nuclei. The deep cerebellar nuclei upon stimulation will then send out axons to go to different areas. Maybe it's going to go to the vestibular nuclei. Maybe it's going to go to the...

reticular formation, maybe it's going to go to the olives, maybe it's going to go to the cerebrum, we don't know. We'll get into that, but all we know is that it's going to stimulate it and it's going to send out a potential, or an action potential. It also can give these axons that go all the way up here to the Purkinje cells. And again, what do we say it releases?

Aspartate. Aspartate, we said, is a stimulatory neurotransmitter that can stimulate these Purkinje fibers. Here's the interesting thing. When the Purkinje fibers are stimulated by these fibers, and we're going to give them a specific name, a very particular name, it activates the Purkinje fibers. They send down action potentials, but here is the interesting part.

These Purkinje fibers, they release inhibitory neurotransmitters, and these inhibitory neurotransmitters is particularly going to be GABA. So this is going to release GABA. which if you know that stands for gamma amino butyric acid. And then these ones here are going to release aspartate. So we'll put ASP here.

Okay, so GABA here, which is an inhibitory neurotransmitter, and then aspartate, which is a stimulatory neurotransmitter. Now here's what's interesting. We said it comes in, stimulates the deep cerebellar nuclei that sends out the action potential to activate other structures in the brainstem. But then it comes up here, activates the Purkinje fibers, and the Purkinje fibers are inhibited.

Again, it's to control the overshooting and the undershooting of whatever movement that we're trying to coordinate. We don't want it to be too excessive and we don't want it to be not enough. So it's important for neural sharpening.

Now, here's the important name for these fibers. These are really important because one thing I need you to remember is that one fiber goes for one Purkinje. One fiber can go to this one Purkinje. This is going to be called... your climbing fibers.

So these fibers here are called your climbing fibers. And the climbing fibers again to remember this one is it is going to be connecting from the inferior olive sending in the information to the deep cerebellar nuclei where it will stimulate it continue to go up to the Purkinje's fibers activate them but they and release GABA that inhibits this deep cerebellar nuclei to play a role with a neural sharpening. That was an easy one.

The next one is a little bit harder. We have other fibers. Let's do these ones in blue.

This next one is going to be what we call mossy fibers. Now here's the thing, mossy fibers come from every other sensory pathway. So every other sensory pathway that you can think of, so watch this, comes in, let's use a different blue. So again we have these mossy fibers, that's better. These are going to come in.

And what they're going to do is they're going to give off axons that go to the deep cerebellar nuclei. The deep cerebellar nuclei are going to get stimulated because guess what this guy releases? He releases glutamate.

Glutamate is a stimulatory neurotransmitter. Activates the deep cerebellar nuclei. The deep cerebellar nuclei sends axons out to control whatever nuclei in the brain stem, which plays a role in the neural sharpening, as well as, again, what? Maintaining posture, maintaining balance, maintaining equilibrium, maintaining the coordination of the movement and motor learning. Now.

These are going to be coming from multiple different structures. We'll go over these in more detail when we get into the pathways. But what I want you to remember is that this is coming from the sensory pathways. We're just going to put that for right now so that we don't go overboard in this area.

We're just going to say sensory pathways. These sensory pathways are going to be coming in and what they're going to do is they're going to give off these axons to the deep cerebellar nuclei. And again, what do we call these fibers?

These are called Mossy fibers. Mossy fibers will give off this stimulus. Activate this, but here's where it gets a little interesting.

It comes up to the granular layer. In the granular layer, it gives off its axons that go and connect with the specific cells in this area. What do we call this area? The granular area, the granular layer.

What do you think those cells are? They're granule cells. So these cells right here are called granule cells. Granule cells.

So what happens is these mossy fibers give off multiple axons. Multiple axons to these granule cells. It also gives some axons off to this little weird looking cell over here. And this is called a Golgi cell. So what is this cell here called?

We're going to write in pink. This is called a Golgi cell. So we'll write this one here.

This is a Golgi cell. These are both in the granular layer. Okay?

So what happens is these monocular fibers come up, give off stimulus to the deep cerebellar nuclei, continue to go up, relieve off multiple axons onto these granule cells, and give off axons to the Golgi cells. They have a name for this structure right here. I'm going to kind of highlight it like this.

This like... tuft of interaction here where you have multiple granule cells and axons of the mossy fibers connecting this is called a glomeruli now again what do we say these fibers are releasing what kind of neurotransmitter glutamate that's a stimulatory neurotransmitter so when it releases the glutamate the glutamate should stimulate two cells the granule cells which will send axons upwards and stimulate the Golgi cells. We'll get to the Golgi cells in just a second, okay? But we'll come back to it, okay? Mossy fibers come up, activate these guys, stimulate the granule cells, and they start becoming stimulated and send axons upwards.

Now, as these granule cells ascend upwards, their axons come upwards, they move through the Purkinje layer into the molecular layer, and then they spread out. They make like a T formation, these parallel fibers. So it comes up, boop, boop, and this one come up, boop. And it's going to cause all these parallel fibers to move all the way across the molecular layer.

Now here's the cool thing about these. These fibers, once they're in this area, they can act on a couple different structures. They have these two important cells in this area.

This bluish one is called a stellate cell. So this is called a stellate cell. And then this one over here, this green one, is going to be called a basket cell. Now, what happens is these granule cells, when they give their axons, they come up here and they can stimulate three important structures. They can give off axons that go to the stellate cells, and they can give off axons that go to the basket cells.

Now, what did we say? Once these are activated, they're going to come up and they're going to give these axons to the basket cells. Whenever they release these neurotransmitters into the basket cells, it actually stimulates these basket cells. So it'll release a stimulatory neurotransmitter that activates the basket cell or can activate the stellate cell. Whenever these are activated...

activated, these stellate cells and basket cells release inhibitory neurotransmitters. Okay? They release inhibitory neurotransmitters, and these inhibitory neurotransmitters are then going to inhibit. the Purkinje fibers, okay, the Purkinje cells. But before that happens, remember we said these granule cells, they send up their parallel fibers into the molecular layer, activate the stellate cells and the basket cells, but guess what else they do?

They give off axons directly to the Purkinje fibers. So now let's show that. So it gives off axons here to the Purkinje fibers.

When it gives off these axons to the Purkinje fibers, it actually stimulates the Purkinje fibers. So what you get is you get stimulus to the Purkinje fibers that then can go down and release inhibitory neurotransmitters here. All right, so the mossy fibers are a little bit of a harder pathway. So let's get this down to like a simple way, right? Because I know it's a lot.

Sensory pathways come in. Remember, this is a bunch of different sensory pathways. First thing, stimulates the deep cerebellar nuclei.

Second thing, comes up, activates multiple granule cells and Golgi cells. The granule cells send up their axons into the molecular layer. First thing it can do is stimulate the Purkinje fibers.

The Purkinje fibers can send down axons and inhibit the deep cerebellar nuclei. Also, to play a role with the neural sharpening, these parallel fibers can also give off axons to the stellate cells and the basket cells. It can stimulate them. When they're stimulated, they inhibit the Purkinje fibers. When they inhibit the Purkinje fibers, the Purkinje fibers are now no longer going to be releasing GABA.

So the deep cerebellar nuclei in that area will fire. This is helping to make sure that in certain areas of the cerebellum, we're having those axons fire, and in certain areas, we're not. Again, it's playing a role with that overall goal here, neural sharpening.

Now, another thing here, as I mentioned, is that these mossy fibers, whenever they act on the granule cells, they also give off fibers to the Golgi cells. When the Golgi cells are stimulated, guess what they do to the granule cells? They inhibit them. So they can also play a role in inhibiting the granule cells.

And again, it's playing a role within all that modification, that neural sharpening activity. Again, guess what else can happen? Not just these mossy fibers can stimulate the Golgi cells, but whenever there's a lot of activity running through these granule cells, the granule cells can also stimulate the Golgi cells.

And guess what the Golgi cells can do? They can inhibit the granule cells. So there's this constant control in this. feedback in this intense circuitry here when it comes to the mossy fiber path.

Okay? So that is how we would describe our internal circuitry. What we're gonna do now is, and I know it was a lot, is we're gonna go ahead and we're gonna take a look at some of the pathways associated with the cerebellum. Alright, so let's finish up here guys talking about the pathways. So if you remember, go back to that first diagram we said talking about appropriate receptors connecting with the cerebellum.

how the vestibule and the semicircular canals are connected to the cerebellum, how the cerebellum is also receiving information from the cerebrum, how it's sending that information out up to the cerebral cortex, and how it actually sends information to some of the nuclei within our brainstem that controls our extra-parameter pathways. We're not going to go into all the pathways. The reason why is, is this, it'll look like a crime scene if we do that here. So, if you guys want to know a little bit more about some of the pathways, So our specifically the pyramidal tracts, like our corticospinal tracts, our subcortical tracts. If you want to learn about all the ascending tracts, go into our neurology playlist and watch some of those.

The reason why is I just want us to focus more on the cerebellum at hand than going into all of those tracts, okay? So how we're going to do this is we're going to go through the connections, the pathways, and basic detail here with respect to the peduncles. I think it's an easier way to celebrate them. them, not celebrate them, separate them. Okay?

So what we'll do first is we'll start with the superior cerebellar peduncles and we'll talk about the relationships there with this one. Okay, superior cerebellar peduncles. Here's what I want you to remember for this one. It has afferent connections and efferent connections. So afferent and efferent connections.

So what do I mean? So the first one we're going to go with is we're going to talk about the efferent connections. So efferent connections, meaning that the fibers coming from those deep cerebellar nuclei are going to go directly to a specific structure. They're coming out of the cerebellum.

So that's what efferent means. Those deep cerebellar nuclei that we were talking about over there, that big green one coming out, it's going to go to specific nuclei out here in the brainstem or the thalamus. We'll talk about what I mean by that.

Afferent pathways is we're going to talk about fibers like the mossy fibers or we're going to talk about the climbing fibers. So all of this should start coming and making sense what we're trying to do here. Efferent, what are the important processes here with respect to the efferent pathways in the superior cerebellar peduncles?

Okay, so let me put this up here really quick here. Let's write over here that this is specifically SCP, superior cerebellar peduncles, is what we're talking about with this one. Now, efferent, what's coming out? The first one that I want you to remember is the dentate nucleus. If you remember we had the dentate nucleus.

I'm just going to do it here in pink for this situation. But we're going to put here the dentate nucleus. The dentate nucleus is a part of the cerebrocerebellum.

Remember that? The cerebrocerebellum, the lateral hemispheres. Whenever it receives signals via the afferent pathways coming from the cortex, what it'll do is it can has two main pathways.

It can send its axons out to two areas. One is it can send it to the red nucleus in the midbrain. Another area is it can send it all the way up here to the thalamus.

So it can send it to the red nucleus and it can send it to the thalamus. Now here's what I got to be careful of. It goes to the contralateral side. So when I do this one, I want to show you this. I got to be particular.

It actually goes to the contralateral thalamus. or the contralateral red nucleus. So the dentate nucleus, let's put that here, dentate, if we want to talk about its etherent pathways, it can send axons to the contralateral red nucleus or it can send it to the contralateral thalamus.

Sometimes it can even connect from the red nucleus to the thalamus. So there can even be axons here that can go from the red nucleus to the thalamus. What is this pathway called? So we have two different pathways.

One is if we go dentate directly to the thalamus. This is called dentothalamic pathway. Now, what's the significance of that?

It's simple. Remember the cerebrum was sending information down to the cerebellum about what it wants to do? The dentate nucleus says, okay, I've done everything.

I've received proprioceptive information, vestibular information, information from what you want to do. What I'm going to do is I'm going to send my perfect, corrected, organized, calculated plan back to you. Guess how it does it? It sends it from the dentate nucleus to the thalamus. Guess where the thalamus can send information?

To the cortex. So now from here, it's going to send this information to the primary somatosensory cortex, to the primary motor cortex, to the premotor cortex, to the supplementary motor area. And now it has the perfect motor plan. Isn't that beautiful?

Now, next thing it can do is it can activate the red nucleus. Now, the red nucleus can go up to the thalamus. That's just a modified pathway.

So we call that the dentorubrothalamic pathway. And it's the same concept here. Same concept. Okay? Same concept.

I'm going to send the information to the red nucleus, go to the thalamus, and up. What can happen is the red nucleus can also get activated. If the red nucleus is activated, if you go back to our extrapyramidal pathways, what does it do?

The rubrospinal pathway. So if the red nucleus is stimulated, it can cross over. It moves to the contralateral side. That's important. I can't stress that enough.

That's important. What will happen is, if it's stimulated, this can... cross over to the contralateral side and move down into the aspect of the spinal cord and activate lower motor neurons that go to our flexor muscles, particularly of the distal extremities. That's called the rubrospinal pathway.

So again, two efferent pathways I want you to remember is dentate to thalamus, dentate to the red nucleus to the thalamus, but again another pathway with this is you can also have the rubro. spinal pathway. Okay.

Another thing is it just doesn't have to be the dentate nucleus that receives information. This is also pretty cool. It can also receive information from the globose and emboli form. Let's do that over here now.

So let's put here we're gonna have the globose and we'll have the emboli form. So we have emboli form and then over here We'll have the globose, again collectively we call these the interposed nucleus. We're going to do one specific color here, but they can send out axons and these axons can go again to the Contralateral red nucleus. If it activates the contralateral red nucleus, what does the red nucleus do?

Decocetes. Goes down to the other side of the spinal cord, activates the lower motor neurons, and then goes out to the muscles. Right?

So that should be a simple concept there. So that's another pathway is you can also have the interposed nucleus go to the red nucleus. Okay? Another pathway that can happen, it's common in both areas, is you also have another one which is called the cerebellovascular vestibular pathway.

Okay, let's write this one down here. Cerebellum vestibular pathway. So what happens here is, this one is actually extremely weird. It's kind of interesting, this one.

Here's our vestibular nuclei located in the medulla, right? Our vestibular nuclei, superior, lateral, medial, and inferior nuclei. Remember we had those Purkinje fibers? Those Purkinje cells.

It's weird because it used to be thought that the vestigial nucleus was the connection. The deep cerebellar nuclei that connected to the vestibular nuclei. Now, they're finding that the Purkinje fibers actually directly leave. They don't even go to the deep cerebellar nuclei.

They actually come out and they are the ones that directly stimulate the vestibular nuclei. If the vestibular nuclei are activated, go back to the vestibular pathway. What can the vestibular nuclei do? They can activate the vestibulospinal tract.

It can go down through the spinal cord, activate the lower motor neurons, and go to muscles. Which muscles? Extensor muscles, anti-gravity muscles, and here's the other one I want you to remember.

If it stimulates it, guess what else it could do? It can go up and do what? It can activate.

What's this structure here called? Medial longitudinal fasciculus. The medial longitudinal fasciculus is connecting what particular structures? The third cranial nuclei, the third cranial nerve, the fourth cranial nerve, and the sixth cranial nerve. What is that specifically responsible for?

The extraocular movements. So, what I want you to remember is, efferent pathways, dentothalamic. Dentorubrothalamic controlling the interaction with the cerebrum letting it know the premotor plan or the motor plan that it calculated Cerebellar vestibular tract is connecting via the Purkinje fibers directly to the vestibular nuclei What are the vestibular nuclei do they go vestibular spinal tract or they can go up via the medial longitudinal fasciculus which controls your extra ocular movements again. This is your Purkinje, okay? Okay, next thing, we'll go to the afferents.

Afferents, again, we're not going to go through all of the pathways here with the afferents because we've already gone over that in our cerebellar video, the ascending tracts of the cerebellum. But for this one, I want you to remember just three important ones. So one is going to be the, we talked about this in the cerebellar video, the ventral spinocerebellar tract. Okay?

And if you remember the ventral spinal cerebellar tract, we're not going to go into all the detail, we did it in that video. It takes sensory information from proprioceptors below what level? L2, L3.

So it's usually, we'll put it here, we'll put below L2, L3 level. Okay? That's an important one.

The other one we did not talk about, but again, it's still an important one, is called the rostrocerebellar tract. So we're going to put this one here. The rostro...

Sarah Beller. tract. This one is taking it from the cervical region. So from the cervical region of the spinal cord. Okay so cervical and even upper extremity region of the spinal cord.

And that one is also going to the superior cerebellar peduncles. And the last one is going to be the tectocerebellar tract. So the other one is going to be the tectocerebellar tract.

Now if you guys know what the tectum is, tectum is actually the superior colliculus and the inferior colliculus. We're going to represent it with this brown little color here. The tectum receives information from our visual. Superior colliculus is visual stimulus. And then the inferior colliculus is going to be auditory stimulus.

That can send information also to the cerebellum to make sure that it helps us to coordinate our eye movements and our head movements in response to visual or auditory stimulus. Isn't that a beautiful thing? So again, let's put that in here.

We also have the tecto. Cerebellar tract here. Okay?

So that's an important one. So, atherin pathways that are going into the superior cerebellar peduncles is going to be the ventral spinocerebellar. If you remember, proprioceptive information from L2, L3 below.

If you want to remember, comes in, crosses over, comes up, and then does what? Goes to the superior cerebellar peduncles and then crosses over to the opposite side. Remember that?

It's interesting. Rostral cerebellar, just remember that it's coming in and it's also going to go through the around the dorsal column area up and then it's going to be taking information from the cervical and upper extremity areas. Tectocerebellar coming via the superior colliculus, inferior colliculus, sending that information based upon visual and auditory stimulus.

These are the main ones that I want you to remember for the superior cerebellar peduncles. Okay, next one we're going to go to is we're going to go to the middle cerebellar peduncles. We're going to do this one right here. So this one is going to be for the middle cerebellar peduncles. So MCP.

Now I want to mention something just because some people usually, some people don't understand it completely, but peduncles. These peduncles, they're not little tubes, they're actually the axons of these fibers going in and out of the cerebellum. So that's really what's making up these peduncles. So if you understand the peduncles, like what those actually are, it'll help you to really understand the connections with the cerebellum. Okay, middle cerebellar peduncles.

Don't know why I have two here. It's one main thing, really important, the most thick, biggest peduncle of all of them. This one is particular.

We're going to do it here in orange because that's where we're going to have these nuclei. Is this going to be related afferent? It's going to be primarily afferent, actually not primarily, all afferent.

Okay, what is this connection? It is via what's called the cortico. It's a heck of a name.

Ponto. Cerebellar fibers. Okay, this is a really, really, really important one. Remember I told you back in the general way, the primary somatosensory, the premotor, the primary motor, the somatosensory cortex, all those areas of supplementary motor, they're developing a motor plan. That motor plan, what are they doing?

They're sending it down to the lower motor neuron, but also what else do they do? Remember I told you, we'll do it here in this color. It's sending this motor plan down.

Let's just say this is one of those areas of the motor cortex or the somatosensory cortex. It's coming down and it comes to these pontine nuclei. So here's the upper motor neuron. And then this area right here where it's synapsing is our pontine nuclei.

Same thing over here. If I were to draw this one, this would be coming down and this would be going to our pontine nuclei. So upper motor neurons. to the pontine nuclei. So that's where we have corticoponto.

From here, these axons cross over, and this will come here, and then these will come over here. And isn't that insane? All of these fibers pass through here and then go to the cerebellum. Now, what is that designed to do?

The cortex is coordinated with what other structure? We can't forget this. What other structure is it coordinated with up here in the cerebrum?

These are two intricate structures. One is going to be the basal ganglia. So it's also coordinating with the basal ganglia. Sending the information down, motor plant goes to the pontine nuclei. Pontine nuclei cross over to the other cerebellar cortex.

Cerebellar cortex receives this information. As well as the proprioceptive information, as well as the inner ear information says, okay, developed a perfect plan. Guess who it sends it back up through? Dentate to thalamus to the cortex.

Or it can go dentorubrothalamic pathway. Isn't that interesting? And it tells it, okay, I received everything.

I've calculated the perfect plan for you. So that one's an interesting one. I love that one. Okay, the last one is the inferior cerebellar peduncles.

So let's put this one here. This is going to be for ICP. ICP.

Inferior cerebellar peduncles. This is a little bit of a bigger one. Okay, we're going to go through afferent first because it's primarily afferent, but we'll talk about a couple efferent ones. Okay. So the afferent ones.

The big one is remember we said for the SCP it was ventral spinocerebellar tract. I want you to remember dorsal spinocerebellar tract for the afferent. So for this one I want you to remember dorsal spinocerebellar tract.

Remember that one comes in, when it comes in it actually synapses on the Neurons of the posterior grey horn goes into the same side of the lateral white column, ascends upwards and goes to the same cerebellum. The other one, and then what is this L level? This is from C8 to L2, L3 area. Some books will even say T1. But this is where the Clark's nucleus is.

The next one is the cuneocerebellar tract. Remember, this one comes in. goes to the dorsal gray horn, actually goes into the dorsal gray horn, ascends up, goes to the accessory cuneate nucleus, right?

And then that goes in via the external arcuate fibers into the cerebellum. That's going to be the cuneal cerebellar, and this is picking it up from the cervical region. So above C8.

The next one is it's going to be receiving information from the vestibulocerebellar tract. The olivo cerebellar tract and the reticulo cerebellar tract. Now let me work through this one, okay? Vestibulocerebellar tract, where is that receiving information from? The inner ear.

So let's write that over here. Let's put the inner ears right here. We're not going to draw the whole structure here. I just want to write inner ear.

Over here, inner. Here, these come in, right? They go to the vestibular nuclei. From the vestibular nuclei, where can these go? They can send their axons in about the balance and equilibrium into the inferior cerebellar peduncles.

And then again here, and then boom. Another interesting thing is, there's actually been research that shows that the fibers from the vestibular cochlear nerve can actually go directly in to the actual cerebellum. Olivocerebellar.

Remember we have the inferior olives. The inferior olives, if you remember, we have the spinal olivary tract, receives information from the proprioceptors, comes into the dorsal gray horn, crosses over, ascends, goes to the inferior olives, and then the inferior olives, they cross over and go to the other side of the cerebellum. So these are also important ones, and they're going to be receiving information, and they're going to be sending the information to the contralateral one, but it's going to be on the ipsilateral side.

So what I mean is, Just to reiterate here, I know that we have a video on it, but let's say that you have the proprioceptors here, sends it in, synapses, crosses over, ascends, goes to this inferior olive, and then this inferior olive will cross over and go to this side, okay? Everything for the cerebellum should be ipsilateral. That's why whenever you see people who have ipsilateral cerebellar ataxia or some cerebellar disease, Whether it be due to multiple sclerosis or B12 deficiency, whether it be due to alcoholism, whether it be due to a cerebellar infarct, whatever it might be, whenever they have that ataxia, it's on the ipsilateral side. Okay, that's important because of all the connections are ipsilateral.

Next thing, vestibular cerebellar connects with the inner ear. Olivocerebellar connects with the inferior olives, which is taking information proprioceptors, right? And this is the important one.

What is this pathway coming in from the inferior olives? The climbing fibers, these are super, super sensitive because remember they interact directly with what neurons? Purkinje. And the last one is the reticulocerebellar.

And the reticulocerebellar is important because it's receiving information about all of our sensory information throughout the entire body. And it's going to be taking that and sending that into the cerebellum, letting it know of what's going on in the body. Okay?

Efferent. Efferent, the ones that I want you to remember here, is going to be... The cerebellum, so we'll say here, let's actually keep it in green here, cerebellum reticular, cerebellum reticular, and cerebellum vestibular.

And some books and some literature will even say cerebellum olivary, but there wasn't a lot of research on that, so I don't want to include that one, okay? So cerebellum reticular, it's simple. You have, we'll go back to this one, cerebellar reticular, fastigial nucleus.

The fastigial nucleus actually connects with the reticular formation. When it connects with the reticular formation, go back to those subcortical tracts. What were the two tracts from the reticular formation?

The medullary and pontine. Medullary is going to be for what? Flexion. Pontine is going to be for extension. Now, if they're activated, they send down those axons through the spinal cord and go and activate those particular muscles.

Cerebellar vestibular, it's going to send information from the Purkinje fibers. Purkinje fibers go directly to the vestibular nuclei. They can go up via the medial longitudinal fasciculus to control extraocular eye movements or they can go down via the vestibular spinal tract and activate the extensor muscles or anti-gravity or postural muscles.

Alright Ninja Nerds, I hope you guys like this video. I hope it made sense. I really do. If it was hard, just continue to keep working at it. It'll come with time.

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Transcript for:Cerebellum Anatomy & Function

Transcript for:
Cerebellum Anatomy & Function