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Hi, everyone. I hope that you can see us and hear us all good now, sorry about the delay earlier, but we're now up and running and ready to go. Um Thank you for joining today's lecture. Um We'll be talking about central and peripheral nervous systems and today's lecture will be given by should be, so I will hand over to you now. Should be um take it away. Sure, thank you. Um Hi guys, I'm tr I'm currently indicating um in Imperial. So I'm 1/4 year medical student and I'm doing my cardiology PSE. So um I'm gonna be running your lecture today, sorry about the delay earlier. Um So before we start, obviously, today is gonna be quite interactive. So please do get your answers into the chat. Um So that we can kind of keep going forward. We're gonna do questions as we go along. So hopefully you should feel a bit more confident about um picking up um what we're learning as we go along and I have got most of the information all in the slides um or in the notes which will be released to you afterwards. And I've also got a summary table. So um you don't need to spend too much time, sort of taking notes and things like that. Um Cool. So let's get started. So, as I said, this is just a little bit by me. If you've got any other questions like specifically um you know, about imperial or anything like that, um um or like BSE options and things like that, then you can ask me later on as well and that's fine. So um the topics that we're going to cover today, firstly, obviously central nervous system and then peripheral nervous system. And at the end, we're going to focus on some SBA questions. So to begin with um kind of the central nervous system. Um but these are the topics we're going to cover. So this is gonna make up the bulk of our lecture and then towards the end, we will move on to the peripheral nervous system. So to begin with, let's start off with the divisions of the nervous system. So this is some basic recap for you. So the nervous system, we can divide that into um the central nervous system and the peripheral nervous system. So the central nervous system consists of the brain and spinal cord, um and the peripheral nervous system consists of our cranial nerves and our spinal cord nerves. So that comes under the nerves group and then we have Gamia as well. Um And these are found outside of the brain and spinal cord So um that's just a quick introduction. Let's move on to the brain now. So if we have a look here, these are the main parts of the brain. So we've got the cerebral hemisphere up here. Let me just grab my um pointer. So we've got the cerebral hemispheres up here which are divided into our lobes, which we'll come on to in a moment. Er, we've got our midbrain pons and Medlar which together makes up the brain stem and then that continues down to form the spinal cord at the back here, we have the cerebellum and then we've got a structure here which is the thalamus and the hypothalamus here together, they can be called aci diencephalon. So it just means the thalamus and hypothalamus put together. So the brain, we can divide into the forebrain, midbrain and hindbrain. Um And each part consists of various subparts. So the forebrain consists of our cerebral hemispheres and the diencephalon. So remember the diencephalon is what is um the thalamus and the hypothalamus put together and then in the hindbrain, we have the pons medulla cerebellum. Um So you might remember from the diagram here. So, Pons Medullar and then the cerebellum put together um gives us the hindbrain. So there's different ways of classifying different parts of the brain. So, moving on um we have our different lobes of the brain. Um Do we wanna get some ideas in the chart? So which what is the blue part, green part, yellow part and the pink part. Could we put some ideas in the chat? Think about the position of the cerebellum. Um I can't see the chat, please. So showing me, would you be able to help with that, please? Nothing's come through. Oh, we've got blue being occipital. Ok. That's the only response so far. Ok. No worries. Ok, we'll go through this uh together in that case. So, um this big blue bit here, that's the front of the brain. So let's orientate ourselves. So this is the front part and this is the back because we've got the cerebellum here at the bottom. So the occipital lobe is found at the back. Um So this pink area here is actually the occipital lobe. The big one part is um what makes up the majority of the hemisphere, which is um the frontal lobe. We have the yellow part here, which is called the parietal lobe. So that's found at the tops and then the temporal lobe, which is, it's sort of in the middle, but it's on the lower half. So it's kind of found um if you're going sort of from front to back of the brain, it's found sort of midway. But unlike the parietal parietal lobe, which is kind of found at the top of the brain, the temporal lobes are found closer to the bottom. Now, they each have very different functions which you will need to learn. Unfortunately, this is a kind of a little bit of rote learning. So the frontal lobe, it's kind of like you can think of them as like higher function. So things like language. So the ability to speak cognitive function, attention, memory, and all of those kind of like um higher level functions are all done by the frontal lobe. The parietal lobe is kind of like your sensory lobe. So um things like touch pain temperature, your sensory limb position. So that's called proprioception. Um Those are all sort of conducted by the parietal lobe, temporal lobe, you can think of it as like the hearing. So it processes auditory information and the occipital lobe is visual information. So these are the main functions and um it is something that can sort of be easily tested through an SBA as well. Now, we do have some other lobes. So these are the lobes that you tend to commonly come across, but there are some extra lobes um which sometimes get examined as well. So, one of them is a lobe here, which is called the limbic lobe. It's quite deep um inside and it's also probably why it's not as uncommonly discussed as the other ones. Um So that's the limbic lobe. Now, the limbic lobe has a lot of other structures in it, like the Amygdala, the cingulate gyrus. Um now, obviously, depending on the level of detail you need for your anatomy exams, um you might go into this in more detail, but um from sort of a um sort of like physiology perspective, um this is probably as, as far as you need. And then you have another one here, which is called the insular lobe. Um So again, it's quite deep, it's buried inside and you need to go through the lateral fissure. So that's what they're holding out here to actually find it. Um And this is to do with autonomic control. And so it's also associated with things like auditory information, visual vestibular integration. So that's kind of like when you see something and when you're doing something and coordinating the balance between them. But as I said, so this is not like the main lobe that controls auditory information, that's the temporal lobe, but this is another extra lobe which has multiple functions, one of which is also processing auditory information. So moving on to the meninges. Now, the meninges are basically like a layer of membranes that protect the central nervous system. So the brain and the spinal cord. So we have three layers. So the dura mater which is the outermost layer, then we have the arachnoid mater, which is sort of the middle layer and the pia mater, which is the innermost layer. Now, our dura mater is made up of two parts. So the periosteal membrane and the meningeal membrane. So the periosteal is the part that's on the outside. And then the meningeal part is the part that comes further inside and it's sort of adherent to the skull. Um the perso one. So, um that's the difference between them. So you can see it here. So we've got the skin like the scalp. Um You've got your Chiara mater. So as you can see the periosteal one kind of covers and lines the skull, whereas the meningo is a little bit deeper inside. And then we've got our arachnoid mater and our pia mater um further inside the pia mater is really, really thin. Um And it kind of follows all of those sort of grooves in the um in the brain surface. So it's literally like such a thin piece of membrane, unlike our mater, which is a lot thicker and tougher. So cerebrospinal fluid. So this is basically um a substance that bas the structures within the brain and the spinal cord. Um Now we'll just go through this together. So, per day. So we have 125 mL of um C A that's produced at any one time. So at any one time, someone will have 125 mL, but per day, you have 500 mL of stuff that's produced. So it kind of tops up throughout the day. Now, it's produced in the core reflexes um of the lateral 3rd and 4th ventricles, the CSF collects in the subarachnoid space and the ventricles and it's reabsorbed via the Arachnoid bili into the superior sagittal sinus. So these are different terminologies that you need to remember and that remember it's produced in one place, it collects in one place and it's reabsorbed via another system. I think this is where sometimes it gets confusing because you see one answer for one question and another answer for another. Um But it's because you need to focus on what they ask. Are they asking why are a CSF produced? Are they asking where it collects or are they asking where it's reabsorbed? Um So you do need to be careful with that. OK. So that was a quick overview of the brain. Um We're going to just quickly talk about the spinal cord and then we'll move on to the ascending and descending tracks, which is what we're gonna focus on mostly today because I know that's something that tends to confuse people. So moving on to the spinal cord. Now, you can see here the spinal cord runs from the brain stem down, you know, all the way down the back and it's very fragile, which is why you've got, you know, like bones protecting you throughout. And you've got spinal cord nerves that sort of emerge between the bones as you can see in this representation here. Um So we have five parts or segments to the spinal cord almost. So there's a cervical thoracic lumbar, sacral, and coccygeal and it is worth remembering how many pairs of nerves we have for each one. So we've got eight cervical 12 thoracic five lumbar, five sacral and one coccygeal. But remember that this is pairs of nerves, the actual bones themselves are different. So in terms of where the spinal nerves exit, they basically exit through the small holes. So these little holes between the bones are called intervertebral parameter. And that's where the nerves exit through. Now, you find meat on either side um at every single level. And basically, in terms of the vertebra, we have. So we have C one, C two, C 3 L1 L2 L3 and so on. Um but the relationship between the nerves and the para changes. So I think this is where sometimes it can be a little bit confusing. Now, to begin with, as you can see here at the top, our C one spinal nerve leaves above the C one vertebra. Our C two spinal nerve leaves above the C two vertebra and so on. However, we only have seven cervical er vertebra. But remember we've got eight cervical nerves. So what happens is up to C seven. So the C seven nerve leaves above the C seven vertebra, which is this one here. But then the C eight nerve is basically leaving below the C seven vertebra. Our T one nerve is leaving below the T one vertebra. So after up to C seven, they all leave above their corresponding bladder number. But then from C eight onwards, they sort of go below the previous one So um T one goes underneath the T one bladder, T two spinal under T two blatter and so on. So that's something to be careful of. Um also from an an anatomy perspective as well. Um Cool. So learning those numbers is important and remember this is to do with the nerves and not the vertebra, vertebra, there's one less of the cervical. Now, we have something called spinal cord enlargements. Um So you can see here the cross sections. Um And you might notice that we have sort of enlargements in the cervical area and in the lumbar area. So these areas are a little bit sort of thicker um compared to the rest. And the reason for that is because the cervical region supplies all the nerves to the upper limbs. Um And similarly, the lumbar region, um you know, everything in the lower limbs. Um And so obviously, that requires a lot of nerves. And so that's why that area is enlarged because there's just a lot going on in that area. Um Again, it's something that is tested sometimes. Um So it's worth knowing and it's also worth knowing the reason why as well. Um So cervical enlargement at the top, upper limb innervation and lumbar enlargement towards bottom lower limb innervation. So it's kind of um logical in terms of the order. Ok. So that completes our section on the spinal cord, we are going to um briefly talk about somatotopy. Um So you might be familiar with that word. Now, somatotopy is um basically this idea that the parts of the brain um can sort of map out which areas they innovate almost. So basically all the different parts of the body are mapped out across the brain. So the top of the body is tends to be found closer to sort of the sides and the bottom of the body like the legs tends to be found towards the middle. So if we imagine that this is a zoomed up version of this, so this is the middle part of the brain. Um And, and this is the lateral sides and as you can see the lateral sides, innovate things like the face, the lips, um and sort of upper body structures. And then we've got sort of in the middle area doing like the trunk hand area and then right in the middle, that's where the feet, toes and things like that are innervated. Um So it's kind of just that idea that um stimulating a specific part of the body actually stimulates a particular part of the brain. Um So it's that idea of it being um mapped out. Ok. So, moving on to the descending tract now, just a little bit of an overview before we start. Now, you can think of the different neural tracts in the body as like different pathways um through which like nervous impulses are transmitted. So firstly, we have um descending tracts. So these are tracks that come from the brain um down to the rest of the body and they're associated with motor function or voluntary movement. Um And they transmit effector information from the brain. So the brain kind of relays information outwards, it's motor information and so on. Um And the major descending pathway is called the corticospinal tract, which you might have heard of before. Now, just a point to note here is that when you're talking about motor pathways, um that's innervating muscles of the face. It's called the corticobulbar tract rather than the corticospinal tract. But it's kind of like the pathway and everything that we're gonna discuss from like a mechanical perspective is the same, but the name is different. So, corticospinal is for the rest of the body. If it's muscles of the face that are being innovated, then it's corb. So um the descending tracts, they originate at the top of the um you know, in the cortex of the brain. And the pathway is made up of two parts. So we have the upper motor neuron which is kind of like um you know, found in the primary motor cortex. And then we have um the second part which is the lower motor neuron and that's found either in the brainstem. Um if the, if the destination is like the head or the neck, um or it's found in the spinal cord, if it's the trunk or the limbs. So, um it's gonna be one or the other. And just to remind you the primary motor cortex is this part at the top in the brain. So it's found in the frontal lobe. So remember we said that the front, the big um lobe at the front is called the frontal lobe. And the primary motor cortex is basically just a specific part of um that frontal lobe. And it's found just in front of this central um gyrus here, um cool and then we have all over your arm. So as I said, it's either fine in the brain stem or in the spinal cord. Now, moving on, there are two parts to the spinal er corticospinal tract. Um So we have the lateral and we have the anterior or ventral. This is just you can use it interchangeably. So some places you might hear it referred to as anterior corticospinal tract, some places it might call it the ventral corticospinal tract. Um But it's essentially the same thing. Um So it's either anterior ventral or we have the lateral corticospinal tract. Now, they are very similar, but there is um small differences which we'll come on to in a moment. Um So you can see here um on this image, um the area that the two tracts occupy within the spinal cord. So the lateral corticospinal tract here is um you know, these parts. So it's kind of like the side and the front. Um whereas the um sorry, the lateral one is sort of the side and um the ventral, which means front um is kind of located closer to the front. Now, the um opposite side is just from the other side. That's why it's colored differently. But this would be also um like dorsal colon pathways and other tracks that we're gonna discuss in a bit. So just as a general sort of rule of thumb, the anterior corticospinal tract. So the bit that sort of travels down the front that innervates trunk muscles and so on. Whereas the lateral corticospinal tract innervates limbs. Um and we wanna discuss what dec is before we kind of move on. So it's a crossing over of fibers to the contralateral side. So these nerve fibers don't necessarily run on the same side. So if it originates in the left side of the brain, they won't run the whole way and innovate the left side, um they, they might cross over depending on which tract we're discussing. Um And so that's what just decussation means. So we'll come to that in a moment. So, whilst the descending tracts or the corticospinal tract starts in the cortex at the top, it then splits. Um So the vast majority around 85% of the fibers will decussate er which means crossing over to the opposite side as they travel downwards towards the medlar. So up to about here, it's kind of common. Um So all of the fibers kind of come up to um to the same point. And then once you reach sort of um the medullar, they start, some of them start to cross over and 85%. So the vast majority of them do cross over whereas 15%. So some of them do continue to go down. So if we look at that there, so it's coming down and then it splits there. So the lateral corticospinal tract, which makes up the majority of the fibers decussate. So it crosses over onto the opposite side and then it comes down. Whereas the green pop, which is the anterior corticospinal tract. So that's only 15% of the fibers that continues to go down. So remember what I said about um the lateral corticospinal tract being um the um pathway that innovates the limbs. Whereas the green one, the anterior corticospinal tract is the one that innovates our trunk muscles. So once it sort of comes down, so you can see the blue one here, it then just sort of exits on the same side. So, and then it goes out that way, whereas the anterior corticospinal tract, what it does is it keeps going down all the way to the level of the spinal cord. So down here and then it crosses over. So at the level of the spinal cord, it crosses over and it's still innovating the opposite side. So more or less they're very similar, but it's just a decussation point that's different. So lateral corticospinal tract. So the majority of the fibers they cross over the medullar onto the opposite side and the exit. Whereas the anterior corticospinal tract, some of them keep going down up to the level of the spinal cord before crossing over. Ok. So that's a quick overview of the descending tracks. Now, we're gonna discuss the ascending tracks, but we will come back to this and if you've got any questions, do um feel free to ask. So, um let's move on to the ascending tract now. So, ascending tract. So this time, it's more to do with um sensory information. In terms of ascending tracts, we have two. So we've got dorsal column pathways and we've got spinothalamic tract. Um and we can further divide this again into the ventral and lateral spinothalamic tract. So again, um if we go back to the image that we saw initially, so um this is obviously just a spinal cord cross section and you can see that the dorsal column pathways are located at the back. So, what we just discussed earlier was the descending tract. So that's the lateral corticospinal and the ventral corticospinal, the remaining areas. So, we've got ascending tracts. That's the dorsal columns, which is this part here. And we've got spinothalamic tract which kind of covers the remaining area and spinothalamic similarly to uh corticospinal can be split further into lateral and ventral. Um So that's kind of the main overview. Now, these ascending tracks are the opposite of the descending. So this time they go up so they start at the sensory receptors and they go up to the cortex um and they relay incoming information this time. So these three different tracks process slightly different types of sensory information. So the dorsal columns they're located um at the back here, they are to do with things like deep touch proprioception. So which just means knowing kind of where your body parts are in space with your eyes closed. So like even if we close our eyes, we kind of know where our hand is or where our leg is and so on. And that's because we have proprioception and that's mediated by this column um here. So it also columns. Um and then we have the lateral spinothalamic tract, which is this part here that is to do with things like pain and temperature. Whereas the ventral is to do with light touch. Now, it is important to memorize these mostly because a lot of ba s distinguish between them. So you need to know that, ok, if their pain is affected, that is to do with the lateral spinal Islamic tract and so on. Um So it is actually important to, to remember what their functions are. OK. So let's start off with the dorsal colon pathways this time. Uh again, looking at the way that they sort of decussate in the in the pathway itself. So all of the ascending tracts as I said, begin at the sensory receptors in various different parts of the body will just take this um level of the spinal cord for today. Um So, the dorsal colon pathway, it can be broken down into first order, second order and third order neurons. So the first order neuron goes from the sensory receptor and it travels through the dorsal root, which is this place here. So, right outside the spinal cord level, um and it travels um at the level of the spinal cord and up to the medullar on the same side. So the ipsilateral side. So if that runs through, as you can see the little dot It's going up um and up to the medullar, it's so the medullar is here. So up to the level of the medullar, it's just traveling on the same side as it sort of came in at the level of the medullar it crosses over. Um and it synapses onto a second order neuron. So this part here, it's not only decorating, but it's also synapses. So this is a new neuron now. Um but it's continuing to take the same information. So we started off here. One neuron took our information on the same side up to the medlar and then it synapses onto our second urine and that sort of crosses over um at the medlar level and goes up. So now we're on the opposite side um of the body and that goes up to um the thalamus and then here it synapses onto a third of the neuron. And that goes up to um the the cortex where it's the information is processed. So there's just a few names to remember. So, the nerves coming from sensory receptors in the lower limbs pass through what we call the gray cell fasciculus. Um And they synapse in the gray cell nucleus. Um whereas the nerves coming from sensory receptors in the upper limbs, they pass through the cuneate fasciculus and they sign in in the cuneate nucleus. So um you can see them, those names here. It's literally like exactly where on the spinal cord does the synapsin happen? It's kind of just like a an area. Um So those are again names that you need to remember. So, gracile is um lower limbs and um cuneate is upper limbs. Um cool now spinothalamic tract. Er So that's the other um ascending tract. Remember. So similar to the dorsal cone pathways. Again, we've got three neurons. So first order, second or third order this time, the first do neuron goes from the sensory receptor which is here. Um And it travels through the dorsal corn at the level of the spinal cord, the same as the dorsal um colon pathways. And here it synapses onto a second order neuron which immediately deficits. So, remember in the previous one, in the dorsal column, we said that it goes up and then it synapses and crosses over here, it's synapses and crossing over straight away, but it's in the spinal cord rather than in the medlar. So it's just a level that is different. So once it's synapses and crossed over, then the second order neuron takes it all the way up here. Um And then at the level of the thalamus, you synapses onto the third order neuron, but here there's no decussation. So remember we've only got one decussation point, both for spinal thalamic and for dorsal colon pathway. Now, technically, this diagram is actually showing a anterior or ventral spinothalamic tract. Um but the lateral spinal thalamic tract is exactly the same. It just sort of travels a bit more towards the side of the spinal cord rather than kind of like through the middle if that makes sense. Um And that's about the, the only difference, everything else is the same in terms of it's still got three order neurons. It's still synapsin at this level. It's still dec heating at this level and so on. So once you've learned one, you kind of know the other one and I don't think that's that gonna be that easily tested cos I think that's a little bit mean. Um Cool. So now that we've gone through the different tracks, we are going to move on. Um Charlie, do we have any questions in the chart? Because I'm happy to go through them. Um As we go along as well, there's no questions in the chat as of yet, but if you're listening and you want to ask the question, put it in the chat and we'll check in and make sure getting answered. Yeah, definitely. Um And we can go through them at the end if um if you want as well. Um OK, so moving on to other tracks. Now, there are some other tracks that you do need to be aware of and so these are called extrapyramidal tracks. So vestibular techo spinal reticulospinal and rubrospinal. Um Now, these are kind of like not very conceptual. So it's kind of a little bit of rote learning. I'm going to leave them in the slides for you to have a look at later, but it's not kind of very high yield if that makes sense. Now, let's move on to an example case. So we're gonna go through kind of what we learned with the ascending descending tracks because I think it's a little bit hard to process sometimes. Um And we're gonna go for a case um as we're working through that. So I'll just let you have a quick read at this. So a 32 year old male patient has fallen onto his back from a ladder whilst doing some diy work at his home. He feels little to no pain on the left side of the body from the T five level downwards. He also feels altered sensation of a fine touch on the right side of his body from the same point downwards, he's able to move his left leg normally, but he has severely restricted movement of his right leg. So I'd let you just have a quick think about that for a few moments. So what do you think um, might be the issue here? What, what part do you think might be affected? So, do you want to have a think about that for a few moments? Ok. So let's have a look of what sort of the key information here is. So I've just put that in red. So little to no pain on the left side from T five downwards, altered sensation of fine touch on the right side. Um Left leg is fine to move, but the right leg isn't, those are kind of like the key information that we need to know cos then we can kind of work out which tracts are being affected where um and we can know is it the right side or the left side of the body that is affected? Now, if we kind of break this down slowly, so let's go back up to the first part. So little to no pain on the left side. So, pain remember is transmitted through the spinothalamic tract and spinothalamic tract decussate immediately at the level of the spinal cord if I find that again. Uh So here you go. So this is a spinothalamic tract. So, uh pain means spinothalamic and spinothalamic as you can see as soon as it enters it dec onto the opposite side at the level of the spinal cord itself. So no pain on the left side from T five downwards suggests that it probably is a right sided um lesion. Um because so on, this is the right. So this is a, so this diagram, it is showing um um the right, so this is, this is the right and this is the left. Um So if the um right side of the body is affected like here, then that's probably a left sided lesion because it's crossing over immediately. Now, if we go back to the question, we have been told that uh he can't feel so altered sensation of fine touch on the right side. So remember, fine touch is the dorsal column pathways, dorsal column decussate at the level of the medlar. So if you're not feeling fine touch on the right side, then it's probably a right sided lesion because the crossing over uh only happens higher up at the level of the medlar. Um And then finally, the movement. So the fact that he can't move the right leg also suggests that it's right sided because again, the corticospinal tract goes up and only decussate at the level of the medullar. So if you want to kind of think of it more simply, and the thing that um any tract that decussate at the level of the medullar, the lesion and the effect will be on the same side, whereas anything that decorates at the level of the spinal cord ie the spinothalamic tract, um you'll find the effect on the opposite side and I think it's better to kind of try and understand why, but you can kind of think of it like this in terms of um exam approach. Um if you're kind of struggling with this. Um Cool. So I've got a detailed explanation that if you want to have a look at it later as well. Um So let's move on now. I've summarized kind of the main things that we need to know for this um into this table which again, you should get um after the lectures over. So these are the main tracks you've got their functions. Um You've got how many neurons they need the decussation point and the lesion, I'd say neurons are probably less likely to be tested. But the other ones, it's really important to remember them. And I think like the kind of harder questions tend to be on like realizing which way they've dec and so on. So I would say this is probably the main thing to take away from today's election. Cool. So we are going to move on to the peripheral nervous system now. So this is the second part of the lecture. Um And it's a lot briefer, we will be moving on to SPS as soon as we're done. So um let's start off with the overview of the peripheral nervous system. So this time, it can again be broken down into two parts, autonomic and uh somatic around system. So the autonomic can then further be divided into sympathetic and parasympathetic. Um And you're gonna have further lectures um you know, that go into uh these in a bit more depth. Um So let's start off with peripheral and somatic nerves. So we've got two different types of nerves. So the peripheral nerves and somatic nerves in terms of peripheral nerves. Uh we kind of discussed this right at the start. So we learned that, remember it's made up of cranial nerves and spinal nerves. Um We have 12 pairs of cranial nerves and we have 31 pairs of spinal nerves, something that's just worth remembering. You probably know your 12 cranial nerves from um anatomy as well. Um But that's what uh makes the peripheral nerves and remember it's pairs. Um So 12 pairs of cranial nerves, 31 pairs of spinal nerves and then with the somatic nerves, um we've got somatic afferent nerves. Um and we've got somatic efferent nerves, so, somatic afferent nerves, they relay information to. So afferent means two. Sorry, I've got that the wrong way around there. Yeah. Um I'll, I'll change it slightly but um so a means to um and if it means from um so to the brain or from the um skin and skeletal muscle and so on. Sorry about that. Guys. Um cool. So these are the cranial nerves and these are our uh our spinal nerves. Um Just to let you know now, moving on to your peripheral nerves. Um Now there is a little bit of that classification that you do need to know for this. So each peripheral nerve it's made up of fasciculi, which means that there's many individual fascicles um that make up the overall peripheral nerve. So each fasciculus has a lot of individual neurons. Um But remember that we need three layers of connective tissue. And um I need to know how you know in what order they're found. So we have the endoneural perineum and the epineurium. Um and it's quite simple really. So um the individual neurons are covered by an endoneurium. So each, each neuron is covered by endoneurium. And then a bundle of neurons is called a fascicle. And each fascicle is covered by perineurium. And then a bundle of fascicles together is a nerve and that's covered by epineurium. Now, if we have a look at the um image, so our individual nerves endoneurium is like the little thin sort of um sheet that covers an individual nerve itself. So like um this and then a bundle of them together is a fascicle. And what covers that is what we call the perineurium. So around each one of these kind of like bundles is perineurium. And then when we've got like a bundle of those, we have epineural So this whole circle together, which is made up of bundles of bundles that is called the epineural. So epineural on the outside and then perineum around, you know, sort of small bunches and then endoneural sort of around every single individual nerve. Um So that's just so that, you know, and finally, reflex action. So reflex action is, it's probably something that you kind of covered from G CSE S onwards. Um But basically a muscle fiber is stretched and that stimulates the sensory receptor, which then sends um a message through the sensory neuron, this synapses onto a motor neuron within the spinal cord. And then the message is passed through um the motor neuron back to the effector muscle, which is the same as the one that the stretching occurred in. And the me the message basically tells the muscle to contract. So that reduces the effect of the stretching. Um There are also inhibitory messages that are passed through another neuron going from the spinal cord back to the antagonistic muscle. So the opposite muscle causing it to relax. Um And this just adds to that effect of the first muscle contracting. So if we've got like this muscle contracting and this one relaxing, then that kind of just adds to that effect. So that's what this inhibitory pathway here is about. Um But yeah, that's probably all you need to know really with reflex pathways. Oh So that again brings us back to our summary team. Um All right. So we can move on to sds. Um I'm just wondering, do we have any questions at all before we move on to that or are we happy to move on? There's no questions in the chat specifically about today's? Yeah, cool. That's good. So let's move on then. So which of the following is not associated with the central nervous system? Um Do you wanna put your answers in the chart? Do we think it's ABC or D? So we've had one answer of C so far and another one saying c see looks like that's the popular answer. OK, cool. Um Yeah, well done guys. So the answer here is see. Um So remember midbrain spinal cord um and the med are part of the central nervous system. Um but the cranial nerves isn't very good. Um How many spinal nerves do we have? What do we think the large majority of people are going for? B 31? We've had one answer of C one answer of a oh no one answer of a again. OK, cool. So last majority of us have gone for 31. Now, anyone think why that might not be right? So you guys are sort of are going down the right line. So you would have seen 31 but have a look carefully at the question if I told you it was actually 62 and not 31. Well, why do you think that might be these spider nuts come on their own. Yes. So someone's just said that it's pairs very good. Yeah. So it's 31 pairs. So remember we said that we've got 12 pairs of um cranial nerves and 31 pairs of spinal nerves. So if they ask you how many cranial nerves do you have? The answer would be 24. And if they ask you how many spinal nerves do you have? The answer would be 62. So try to look out for things like that. And so you don't sort of just fall into unnecessary traps. But yeah, well done guys for remembering that it was 31. Um Depends cool moving on. So where is the substance that fills the subarachnoid space produced? Be careful. So remember the question is about where it's produced, not where it accumulates and not where it's reabsorbed. We've had two people say C someone said DD again, that's very good. Actually. So well done guys, the answer is CD is actually not completely wrong. So this VCD as well, that's still a good answer. So we're done. Now, this question essentially has two parts. So firstly, we know that um it's CSF that fills the um subarachnoid space, but now we need to think about, you know, where is the CSF produced? Um And yes, it did say we did discuss this earlier. So the CSF is produced in the choroid plexus of the lateral third and the fourth ventricles. So A and B are wrong because, so CSF doesn't sort of go, it's not really relevant to the subdural space, subarachnoid space. It is collected in the subarachnoid space, but it's not produced there. Um The reason why I said D is not completely wrong is because yes, it is produced in a particular part of the third ventricle, but it's not the best answer option here. So in an SBA um the answer would be c because it's a ch ch choroid plexus of the ventricles. Um and not just the third ventricle if that makes sense. So it's a specific part of the ventricle. Um Cool, hold on now, moving on. Um So a wasp is flying near a person's eye and they need to contract the muscles around it to prevent it from touching their eye. Which tract is involved in this. Any ideas we've had one answer come in of C C OK. Any other DDA bit of a debate CD? OK. Um So I don't know. So you've eliminated spinal thalamic and dorsal colon. So you are right in that. So this situation is associated with motor pathway because we're talking about contracting the muscles. Um and this involves sending information out of the brain to the muscles um so that we can cause a contraction. Now, you are right in saying that the main sending pathway is the corticospinal tract. So those who you see are not completely far off, but remember what we said earlier right at the start um about the fact that if it's to do with a person's face and the contractions, um then it's called corticobulbar. Whereas if it's anything to do with the rest of the body, so head and neck, it's corticobulbar. Um anything to do with the rest of the body, it's corticospinal. So pathway wise, you're not wrong to say corticospinal. But um it's just that we're not talking about like the right part of the body here. So because it's the eye, it's the corticobulbar, but the same situation, if it was like the hand or the leg or the, the trunk, then you'd be right in saying corticospinal. So um what are those for those UD? So that's kind of am point to remember. Um Cool now, moving on to the last one. So this is quite sort of tracked heavy. So I'll give you a few moments to have a go at this. This one is quite tough. Um So we will discuss it. So we've had someone say, OK, sorry, was that ac or DD? OK. Cool. Any other ideas? Not had anything come through yet? OK. So well done to the person who did choose uh d because that is the right answer and that's actually quite difficult, so well done. Um So let's break it down. So we've been told that she's unable to move her left limb and trunk. Um And that means that the corticospinal tract is involved. Um because that's motor function being affected and motor function is coordinated by the corticospinal tract. Now, the corticospinal tract travels upwards on the ipsilateral side and it only dec at the level of the medlar. So remember that if it's decorating at the level of the medullar, then the side that is affected must be the side of the lesion. That's the same. So that suggests that this must be a left sided lesion. Now, let's keep moving on. So they've, she's, they've also told us that she can't feel any pain on the right side of, of her body. Um And so that means pain means spinothalamic. And remember we said spinothalamic dec immediately. So at the level of the spinal cord, and remember we that if it decorates immediately, then the effect is gonna be on the opposite side. So if she can't feel the right side of her body, then that means it must be an issue on the left side. Um So it's a left sided lesion. So that again, backs up our initial one. So we initially thought it was left sided because of the um the motor function involved. Now, the pain is also backing that up again. Um Now we've got two answer options that say left sided, it's quite difficult to distinguish, you know, is it a left sided C three lesion or a left sided C five lesion? Um D do you have any ideas if someone chose D um do you have any ideas? Why, why is it C five and not C three? Not got anything yet? Maybe that high pain. So, even if we got up to sort of understanding that it's a left sided lesion, then that's still great because this last part is quite um difficult to, don't worry. Um We had someone say dermatome, which is kind of right. Um But so we're not quite talking about dermatomes because it's not um sensory information that we're dealing with, but it's kind of like the right kind of idea. So it's to do with which parts of the body are affected. Now, do you see that they've told us that the effects are on the hands, arms, trunk and legs. Um but her head, neck and shoulders are unaffected. Um So we know that the nerves up to C four are working. Um But the brachial plexus isn't working because otherwise we wouldn't have effects on the, on the hands and the arms and things. So therefore, C five onwards must be affected. So we know up to C four is fine because the head, neck, shoulders are fine. Um But C five onwards must be affected because she's seeing effects in her hands and arms and so on. Um So therefore, overall, we know that it's a left sided lesion at the C five level. Um But as I said, if you got up to sort of left sided and weren't sure if it's B or D, then that's still really great. Um, because you've kind of worked out, um, the pathways and the decorations. Um, but I think that is something that sort of does take a bit of time to get your head around. Um, cool. And that brings us to the end. Um, I don't have a feedback form actually, but do we have any questions? Um, at all? I, it should come to everyone's emails after the event and after filling in the feedback form, you should be getting access to the slide and the recording for today. So you can revise again. Um If that doesn't happen for whatever reason, please just drop us an email or get in contact with us. Um But that's usually how it happens. Thank you so much for presenting today. I'm sorry, everyone about the delay, but that was an amazing presentation. Definitely worth it. Um Thank you for everyone who attended today. Um The feedback form should be coming to everyone's emails. Um Please fill it in so you can get access to all of the uh slides and the recording and um yeah, I hope you will find it really useful. Um Beam is holding a whole load of teaching lectures on neurology. So please come to the next one. It should be on our Instagram page. Um If not now very, very shortly. So, yeah, write it in your diaries and uh thank you all for coming that's ok, thank you guys. Um and also if you've got any questions, I'm happy for you to email me as well and I'll get back to you guys. Um but yeah, what?