All right. So, this lecture is going to cover um kind of an introduction to the peripheral and central nervous systems. Uh specifically looking at things like uh the peripheral nervous system as well as the vascular and cerebral spinal fluid um systems and cranial nerves. So, we will get more into different parts of the brain. what they do, where they are, things like that next week. First, there are a few key directional terms that you need to know. If you've already taken anatomy or physiology, you should be all too familiar with these. For the rest of you, these may be somewhat new terms. Now, we're talking first, we'll start with medial and lateral. Medial and lateral refer to toward the midline and away from the midline. Medial is like the median or the middle. So think about the median of a set of numbers. You put them all in numeric order. The median is the middle number. Or you might think of the first of the median on a road which is the grassy patch in the middle. So the medial refers to a structure that is toward the middle of the body and lateral refers to a structure that is away from the middle. So for example, we'll talk about the medial and lateral preffrontal cortices. This refers to the very front of the frontal lobe, right behind your forehead. And medial means the stuff closer to the middle of your forehead. Whereas lateral is going to refer more toward the sides of your forehead. Think just behind the outside edges of your eyebrows. Medial and lateral always going to be pretty straightforward, but dorsal and ventricle and anterior posterior can get a little confusing at times because these are in reference to four-legged animals. Because of this, talking about the peripheral nervous system and the spine can often seem like we're talking about a different direction compared to when we're talking about the brain. You'll see at the top of this image that dorsal refers to the top of the brain as well as the top of the spine in a cat. This is why we talk about a dorsal fin for a whale or a dolphin. This is the fin on their back. In contrast, you can see in the image on the bottom that dorsal refers to the top of the head, just like in the cat, but the back of the spine. When we refer to the spine, anterior is the top and dorsal is toward the back. But if you think of it as toward the head or away from the head, and toward the chest or away from the chest, anterior, posterior, and ventricle, dorsal are just the same for two-legged and four-legged animals. This won't be a huge issue for us because we're generally going to be talking about the brain in this course though we will sometimes talk about the spine and as you'll see in just a moment. So anterior means toward the nose and posterior means toward the butt. But you will also see these referred to as rostral and codle. We'll talk about the koda aquina which is the very tail end of the spinal cord. This is called the kada aquina because it looks like a horse's tail. Hence the aquina rostel means toward the nose. If it helps, you can think of a rhinoceros, which has that big horn on its nose. I don't know why my brain keeps track of it that way, but it does, so it might help for you, too. You also see a few other terms, including hypo and supra. Hypro just means below. You might have heard of a hypodermic needle, which goes below the skin. We'll talk about the hypothalamus which is located you guessed it below the phalamus. Supra means above. We'll talk about the supra kaismatic nucleus of the hypothalamus when we talk about sleep. This is the part of the hypothalamus that is right above the optic cayazm. This part of the brain detects light light and dark signals. So it makes sense that it's right above a major pipeline for visual information. Broadly speaking, we can divide the nervous system into two primary divisions. The central nervous system and the peripheral nervous system. The vast majority of this course will cover the central nervous system, which consists just of the brain and spinal cord. But we will talk some about the peripheral nervous system, which is basically everything that goes from the brain and spinal cord to the rest of the body. It sends instructions to your body to make it perform various processes and it receives messages from the body to inform the brain about these processes as well as information coming in from the environment. The peripheral nervous system is further divided into the autonomic and somatic nervous systems. The somatic nervous system is responsible for bringing the sensory information in and for sending out commands to control voluntary movements. The autonomic nervous system is responsible for controlling and monitoring all of the involuntary processes. We'll get to what those are in a minute. But an important thing to remember is the difference between apherrant and epherent messages with these. These will have the same basic meaning for both somatic and autonomic. Apherant with an a messages alert the central nervous system to what is happening. They bring messages from the periphery to the brain and the spinal cord. Epherent messages with an e exit the central nervous system to the rest of the body. They take commands from the central nervous system and deliver them to the organs and muscles. Probably the easiest way to keep track of this is what's called the same Dave pneummonic. The same sme part of this probably makes sense. Sensory neurons are apherrant and motor neurons are epherent. Aphrant neurons alert the central nervous system to what is happening inside the body as well as in the outside world. And this information is being brought in via sensory neurons. In contrast, motor neurons are epherent because they exit the CNS and bring messages to the muscles and organs to enact the actions indic in initiated by the CNS. The Dave part is referring to what which road the sensory and motor neurons take around the spinal cord. The image here is a cross-section of the spinal cord. So, think about someone standing up upright and slicing the spinal cord horizontally. The spinal cord is in the middle here. So you can see all of this right in here. This is all spinal cord. But there are these arms referred to as roots coming off. So some on the top, some on the bottom, both on the left and the right hand side. This image, the top is dorsal and the bottom is ventral. The arms coming off of the top of the spinal cord are therefore dorsal and the bottom arms are ventrical. So these up here are our dorsal roots and you can see right here it says dorsal root. Down here are our vententral roots and you can see right there it says vent root. So the dorsal so you should be able to then figure out the rest of the same Dave pneummonic. So the dorsal arms here carry apherant information which is the sensory information that's coming in. In contrast, the vententral arms down here carry the epherent information which means that is where neurons with motor commands leave the spinal cord. Again here is that sematic nervous system. This is the sensory information coming in from the body and from the outside world which we refer to as the sumata sensory information. This is in part touch information from your skin. But as we'll talk about when we cover movement, this also includes information from nerves inside of your muscles and joints that tell you how your how much your muscles are stretched or contracted or relaxed and how much your joints are bent. This information comes in via those sensory aference in the dorsal horn goes up the spinal cord and is processed in the sensory cortex at the front of the parietal lobe. Motor information on the other hand is processed at the motor cortex at the back of the frontal lobe. So here is our sensory cortex here at the front of the parietal lobe and then just on this side right here at the back of the frontal lobe is our motor cortex. So the motor information gets processed at the motor cortex. It then travels down the spinal cord and exits through those epherent neurons in the vententral horn and goes to the muscles to trigger movement. So we've had central versus peripheral nervous systems and we've said peripheral is divided into somatic versus autonomic. We already covered somatic and now autonomic. So autonomic is further divided into the sympathetic and parasympathetic systems. Your sympathetic nervous system activates your fightor-flight response. It is responsible for mobilizing energy in order to deal with a potential threat. So if you see a lion coming into the room, your sympathetic nervous system activates. It redirects energy to the organs that need it in order for you to survive. It sends oxygen and glucose to your heart and to your voluntary muscles so that you can run away or fight the threat. It makes the bronchia in your lungs expand so that you can get more oxygen in with each breath. It also does some weird things like stimulating the muscles inside of your eyes in order to dilate your pupils or to make them bigger. This allows you to take in more visual information to identify potential threats. Your sympathetic nervous system also turns off any processes that are not strictly necessary right now, such as digestion. You shouldn't be wasting money or wasting energy on digesting dinner if you're about to become dinner. Then you have the parasympathetic nervous system. Parasympathetic is more active when you're at rest. And it's all about conserving energy so that you have that energy next time you experience a threat. This is basically the opposite of the sympathetic nervous system. And you'll see in the next slide that the actions are pretty much opposite. Sympathetic turns off digestion and parasympathetic turns it on. Sympathetic increases your heart rate, but parasympathetic slows it down. Sympathetic increases your blood pressure to make sure you get glucose and oxygen to all of your muscles. Parasympathetic decreases your blood pressure when you're at rest because having constantly high blood pressure puts a lot of strain on your arteries and can cause a stroke or a heart attack. Each of your organs receives input from both the sympathetic and the parasympathetic nervous systems. And the level of activity of that organ will depend on the relative level of activation from each of these systems. This diagram is showing the different actions that the parasympathetic and the sympathetic nervous systems have on different organs. So you can see here the different actions um by the parasympathetic nervous system in green and the sympathetic nervous system in orange. Looking at this second one here, right here and right here, you can see that the parasympathetic nervous system increases saliva production because saliva production is one of the first steps in digestion. The sympathetic nervous system inhibits or decreases saliva production because it turns off digestion more generally in order to focus energy on more immediate functions like running away from a lion. Now let's move on to the structures of the central nervous system. Since we started in the peripheral nervous system, it only makes sense to move into the central nervous system via the spinal cord. And as we've already covered, the primary role of the spinal cord is to relay messages between the peripheral nervous system and the brain. There are a few things the spinal cord does directly such as reflexes, but it's mostly just in charge of passing along orders from the brain to the peripheral nervous system and giving status updates from the peripheral nervous system to the brain. One important thing that we can see starting in the spinal cord and continuing throughout the brain is the difference between gray matter and white matter. We haven't talked about neuron structure yet, but all you really need to remember for this is that most neurons consist of a cell body, the soma, and appendages. Some of these are arms coming off called dindrites, but there's usually one much larger appendage coming off called the axon that is responsible for transmitting messages from the cell body to other neurons. Gray matter is made up of the cell bodies of these neurons as well as inter neurons which are smaller nerve cells that transmit over very small distances. White matter is made up of the axons. These have a substance called myelin that wraps around them and insulates them to allow the messages to send more effectively. We'll go over this in way more detail next week, but this is important for understanding the spinal cord because you can see that the gray matter is only right in these center areas, right in here and in here. These areas are known as the and vententral horn. Everything around that is white matter, which is axons of other neurons traveling up and down the spinal cord. We'll go more into this diagram when we talk about movements, so you don't need to know all of the details just yet. If you look at the image on the right, you'll see that the spinal cord is divided into a few different divisions. Cervical, thoracic, lumbar, sacral, and coxal. And these pretty well line up top to bottom with the vertebral divisions. So the divisions of the vertebrae. So you've got your cervical vertebrae here, your thoracic vertebrae here. It's not exact, especially when we get to these blue and orange sections, green and blue and orange sections down here. This is because the gray matter of the spinal cord ends long before the spine does, but there's still nerves that leave through those lower vertebrae. You can see this better in this middle image here. So, I'm going to zoom in a little bit so you can see it better. Oops. Here we go. You can see that the spinal cord itself ends up near L1 or so right up here or the first of your lumbar vertebrae. But there are still nerves that are coming out way down here, way down those sacral vertebrae. Now the image on the right over here is showing where the cell bodies for these are and they're then their axons reach down to where they're supposed to leave the spine. Think about stretching your arm to reach around the shower door to get your towel. This produces this tailike effect in the lumbar spine. Down here um this is as I mentioned before this is called the katada aquina. Down here is also where we do spinal taps, also known as a lumbar puncture. Get it? Because we're in the lumbar spine. These regions are still part of the central nervous system and still contain cerebral spinal fluid, but we don't run the risk of damaging the cell bodies by accidentally sticking them with a giant needle. These axons down here can very easily move out of the way. So, we don't really need to worry about damaging them with a needle during a lumbar puncture. You might be thinking, isn't that lumbar region also where we give epidurals during birth? Yes, yes it is. And if you thought that and have already done the reading, you might say, hey, epidural sounds like dura matter. And you would be right again. An epidural is any kind of injection, in this case pain relief, that goes into the space between the vertebrae and the dura matter. When we administer an epidural during birth, we're affecting the sensory nerves coming in. But because we're not piercing the dura matter like we do in a spinal tap, we're not actually going into the central nervous system and therefore can reduce the risk of infection. But what is the duramatter? Duramatter is one of several meningis that you have surrounding the brain. So what are meningis? Mani are basically layers of covering that serve various purposes in the brain. When you open up the skull, you'll have several layers of these to go through before you get to the actual brain cells. The first of these is the dura matter. The main job of the duramatter is just to protect the brain. Duramatter translates to tough mother and you will see this yourself when we do the sheep brain dissections. It is really tough, kind of like leather. It serves as a type of cushion for your brain and protects it from the relatively inhospitable environment that is the inside of your skull and spine because it encapsulates the entire central nervous system including the spinal cord. In fact, if you look back at the previous slide, we can see down here where it shows the end of the duramatter right here of that baggie so to speak near the sacral vertebrae. Now the next meni the these menises is the arachnoid membrane. It is called arachnoid because it is almost like a spiderweb. Again you'll be able to see this very well when we look at the sheet brains. The arachnoid matter has a pretty uniform surface on the top. So you can see this kind of I'm going to switch pencil cover colors. There we go. You can see kind of this kind of uniform shape in here. Uniform level. um has all of these filaments that are coming down. These reach down and they make connections to the next layer which is the patter. We can see here that there are lots of gaps in between these filaments and this is referred to as the subacoid space. This is where most of our blood vessels travel around. It's also filled with cerebral spinal fluid and therefore provides a lot more cushioning for the brain. The last is the patter. This translates to pious mother and it is directly attached to the surface of the brain. So the piamatter is right down here. So it is kind of the bottom layer that the sub the arachnoid membrane those filaments are connecting to. Um so the pometer again is going to serve several purposes including cushioning. Uh it also helps with the flow of lymphatic fluids and cerebral spinal fluid. But one really important thing that it does is it provides some structural support in the spinal cord. If your spinal cord gets compressed, for example, from jumping or running or doing gymnastics, you need some constraints in there. You need some structure in there. The patter helps to keep it from smooshing so much that it damages the neurons themselves. And its elastic properties help the spinal cord tissue to go back to the normal shape quickly and easily. Once you get through the very thin pia matter, congratulations. You are officially at the brain. Now, even if you have not heard of these menes before this class, you've likely heard of an illness that directly affects them, menitis. Menitis is an inflammation or swelling of the meninges due to a bacterial or viral infection. One of the first signs of menitis is a severe headache, which is often followed by neck stiffness. If you ever have a really really bad headache, like worst headache of your life, try bending your neck to touch your your chin to your chest. If this is much harder for you to do than usual, especially if turning your head left and right quickly makes the headache much worse or if you have a sudden very high fever, go immediately to the ER. Do not stop. Do not collect $200. Your meninges are swelling and putting pressure on your brain and could cause you to lose consciousness. Menitis now is relatively uncommon but it can be extremely contagious. This is why many residential colleges like handover require you to have a viral menitis vaccine in order to live in the dorms. In fact, if you have not gotten a vaccine for viral menitis, I strongly recommend that you get one. Like I said, menitis is pretty uncommon. It is relatively rare, but if you get it, it can be very deadly. Uh because it's really hard to treat infections, be they bacterial or viral, inside of the central nervous system. I've mentioned cerebral spinal fluid a couple of times, so let's talk about it. You can think of cerebral spinal fluid as kind of the blood for your brain. While you do have veins and arteries in your brain, a lot of that work in the brain that's usually done by the blood is instead done by cerebral spinal fluid, including removing waste and providing a consistent environment for the brain cells. The average person has a little more than half a cup of cerebral spinal fluid in their brain and spinal cord at any given time. And you replace this three to four times a day. Now, for comparison, it takes about 2 weeks for you to replace all of your blood. In addition to providing some nutrients in a stable environment and removing waste, cerebral spinal fluid also provides a ton of cushioning for your brain. As you probably know, the skull is made of bone and bone is hard. Your brain is squishy. You move your head a lot on a daily basis. And if all you had protecting your squishy brain from the hard skull was the meninges, you would have a lot of dead brain cells pretty quickly. Cerebral spinal fluid acts basically as a water cushion. Cerebral spinal fluid is produced by regions called the koid plexus. These are inside of all of your ventricles. It then travels through these ventricles down the spinal cord and through the subacoid space. Eventually, it makes its way through the dural sinuses, which are channels in the dura matter, which empty the cerebral spinal fluid and as well as some blood into the jugular vein. Cerebral spinal fluid can be incredibly useful for telling us about the environment inside of the central nervous system in a way that blood cannot. We'll talk about exactly why blood isn't very useful in a bit. But this is why we have to do things like spinal taps if we suspect an infection in the brain or spinal cord such as menitis. There are also some researchers who measure things like how much dopamine was released under different conditions by measuring the amounts of dopamine byproducts in the cerebral spinal fluid. They can't tell exactly where it is being released. The same way a blood draw can tell you if you have an infection, but it can't tell us where that infection is. But it does allow them to get a snapshot of what's going on in the brain by basically looking at the sewer system. Next up are the ventricles. These are large empty spaces inside the brain that contain the cerebral spinal fluid. You have four key regions, four ventricles that you need to know. the lateral ventricles, the third ventricle, and the fourth ventricle, as well as the pathways between these ventricles, which we'll talk about. The lateral ventricles are these pretty large, vaguely C-shaped regions. If you look at the brain headon, as we can see in this image, uh you can see that there is a lateral ventricle on each side. So there's one on the right and there's one on the left. If you cut the brain perfectly in half down the center, so if you were to cut brain straight down the center like that, or you can see that kind of right in here, you probably won't be able to see the lateral ventricles because they don't actually meet. These would technically be ventricles one and two, but we don't want to show favoritism to the left or the right side by calling the other side the se second ventricle. So we just call them both lateral ventricles. The third ventricle is right in the middle. If you look at the image on the left here, you can see um you might be able to see this kind of vaguely face looking thing. So, we've got an eye here and an eye here. And this is kind of making up the nose. The eyes, these two eyes right here and right here, these are your lateral ventricles. We just talked about this nose spot right here. This is your third ventricle. An image on the right over here. You can see the lateral ventricle here. Uh this is the lateral ventricle for the other side. And then this yellow right here, that is going to be our third ventricle. Whereas the lateral and third ventricles are in the main part of the brain. To get to the fourth ventricle, we have to kind of head down toward the spinal cord. Our last stop is what is considered in what is considered the brain is the um kind of hindbrain and the cerebellum right here. The space in between the hindb brain and the cerebellum right in here. So, I'm going to switch over to switch over to I'm gonna switch to green. That might make it easier. This space right in here, you can see it with the green here in the yellow. Uh this is the fourth ventricle. Um over from this image from before, we can see the fourth ventricle is here in this purple. As I mentioned before, the cerebral spinal fluid needs to flow throughout the ventricles as well as down the spinal cord and around the brain. So even though for instance the lateral ventricles and the third ventricle are separate spaces, there need to be pathways that connect them. The exception to this weirdly is the lateral ventricles. They do not connect to one another. The tubes going from each of the lateral ventricles to the third ventricle are called the intra ventricular fammen framina uh also known as the monro foramina. Foramina is the plural of fammen but we use this because we have a separate tube that is going from each of the lateral ventricles to the third ventricle. Uh here on the photo on the image on the left you can see this probe is going. So we've got our third ventricle right in here. So we're kind of in the middle of the brain here. So the third ventricle normally would be right in the center. It doesn't actually look very much right now. So third ventricle is here. Lateral ventricles. We've kind of removed a little piece right here so that you can see into that lateral ventricle. And you can see this probe is driving straight through that Monroe Foreman uh for famemen the channel going from the third ventricle to the fourth ventricle. So going from the third ventricle in this space and the fourth ventricle right down here is going to be going through here. Um and this space is known as the cerebral aqueduct or the sylvvian aqueduct. Uh and so that space is just right in here. Uh you can also see it in red right here on these uh in the lateral ventricles you can see or the the Monroe firmina you can see in the the light teal right here going from the lateral ventricle to the yellow. Now once the CSF is in the fourth ventricle it can then go down it can go into the subacoid space by going around the cerebellum. So coming down the fourth ventricle and going around the cerebellum kind of like this. Or it can go into the spinal cord via what is called the central canal which is in the green here. You can see that going down like that. When we look back at the crosssection of the spinal cord from before. So looking at this one here, we can see that dark blue spot right in the middle. That is the central canal. The CSF can travel all the way down the spinal cord and into the lumbar spine, which if we zoom in here, we can see down here the the cerebral spinal fluid is going to travel all the way down here, all the way down to the codina until the very base of the matter down at the end there. And then it has to travel all the way back up and get up to the brain. And then it's going to go out through those dural sinuses. The brain also has a pretty extensive vascular system that is supplied by two main pairs of arteries going into your head. The corateed and vertebral arteries. Corateed arteries are the ones on either side of your neck where you can very easily check for a pulse. Your vertebral arteries enter your skull by the back by the cervical vertebrae. Your left and right corateed arteries each split into internal and external branches. External basically just does stuff in your face. We're going to largely ignore that. But the left and right internal corateed arteries together supply about 23 of the blood flow to the brain. Once inside the skull, the internal corateed branches again to form the anterior and middle cerebral arteries. Anterior cerebral arteries provide blood flow to the areas in purple here which include some of the most forward areas um as well as these medial structures here. So this is kind of your the kind of looking in the middle. This is sliced. Um, basically like this is this is the inside. Um, and it it's opposite of this view right here down here. Um, so we're looking at the some of the frontmost areas as well as those medial structures. The middle cerebral artery gets kind of the sides over here. We can see the side over here. Uh, as well as some of these deeper structures here in pink. blue areas are supplied by the vertebral arteries that come up the back of your neck. They enter the skull back by the spine and they merge together to form the basler artery. The baselor artery then splits. So we can see the basler the vertebral arteries coming in here. They come in uh via the spine kind of coming in on either side here. They're going to merge to form the basler artery. So this is your basler artery coming together right here. Um the basler artery is then going to split again to form the posterior cerebral artery which does all of this stuff in blue. All of this stuff back here all of this stuff. All of this stuff back here and blue. Um and artery also provides some blood flow to these areas here in the middle uh which is known as the hindburn. A lot of your these are a lot of your basic life functions like breathing and your heartbeat. You can also see here in this middle part right in here the anterior, middle and posterior cerebral arteries form what is called the circle of willis. This is really important failsafe structure that basically allows us to make sure that we continue to get blood flow to the brain even if there's a blockage somewhere. So if one of your vertebral arteries was damaged, your posterior cerebral artery could siphon off some of the blood coming in from the internal corateed in order to do its job. This is not a good long-term fix, but it protects the brain from permanent damage in the short run. Lastly, we'll talk about cranial nerves. These are technically still peripheral nervous system, not central, but it made more sense to talk about them here rather than back when we were talking about peripheral nervous system. So, we're jumping backward. Now, you have 12 pairs of cranial nerves, some of which receive sensory information, others which send motor commands, a lot of them do both. They are called cranial nerves to designate that they don't come in via the spinal cord like most of your sensory and motor nerves do. You have 12 pairs because you have one for each side of your body. Uh they're numbered 1 through 12. And the numbers generally, but not entirely, go up as you move from the rostal surface to the codle end of the brain. Cranial nerve one is your olfactory nerve. It is the most anterior of your cranial nerves and it is responsible for receiving olfactory information or your sense of smell. We often divide this into two sections. The olfactory bulb and the olfactory tract. The bulb is the part responsible for receiving smell information. It has projections that go through your skull at an area called the cribopform plate. That's what in this green here. You can see we have the olfactory bulb here. It is sending these projections through the skull. The skull there kind of looks a little like Swiss cheese. Uh so it sends these projections through the cribopform plate and into the roof of your nasal cavity to detect chemicals that provide olfactory information. The olfactory tract is where that smell information travels to a few different regions in the brain that process smell. Now, if you ever have the misfortune of meeting a braineing amoeba, it most likely entered via this route. This is also why you should never use basic tap water for things like a netty pot. If you're ever doing nasal irrigation, you should always boil the water first and then wait for it to cool down before rinsing your nose and sinuses with it. Or else you could be providing microbes with an uber directly to your olfactory nerve and then into your brain. Cranial nerve two is your optic nerve. This brings visual information from your eyeballs to your brain. The optic nerve does a funky thing in that you'll see it creates kind of an Xshaped path. So you can see that kind of this X shape here. This point is referred to as the optic kayazm. When information comes into your eyes, it is initially detected by your left eye versus your right eye. But your brain does not process left eye versus right eye. It processes left field of vision versus right field of vision. You can see this here in the blue versus red. Because of the way that your eyeball is curved, the right half of your right eye detects information that is to the left of the middle. Your left or this is also referred to as your left field of vision or your left visual field shown in blue. The left half of your right eye. So, we're looking over here. The left half of your right eye detects the stuff that is to the right or your right visual field which is in red. So, each eye takes in information about the left and right visual fields of information. But the right side of the brain only cares about information in the left visual field. And the left part of the brain, left half of the brain, only cares about the right visual field. I know it's weird, but the brain likes to play opposite day for a whole lot of things. So, get used to it. So, if the information coming from the right eyeball, half of it needs to go to the right side of the brain. So, we've got our right eyeball here. Half of this information needs to go to the right half of the brain. Half of it needs to go to the left half of the brain. The same is going to be true for the left eyeball. This crossing over process takes place at the optic kayazm. If we zoom in, you can see that the red from each eye goes over here. So the red from left goes to the left side. The red from the right goes to the left side. And then the same thing for the blue. The blue from over here goes to the right side. The blue from over here stays on the right side. So we can see that this crossing over takes place where some of the information is going to cross to the other side but some of it's going to stay on that same side. Now the optic kayazm will likely be one of the easiest structures for you to identify on the sheet brains. So make sure you keep an eye out for this. Next, we're going to get into a cluster of three different cranial nerves that are responsible for eye movements. Yes, one nerve for all of visual information, but three just to control the way the eye moves. These are your cranial nerves 3, four, and six. Three is also called the oculum motor nerve. Four is the tlear and six is the abducence. As you can see from the list of muscles it controls and probably by the name, you can tell that the ocular motor nerve does the most when it comes to eye movement stuff. It controls the superior rectus and inferior rectus which are responsible for looking up and down as well as it controls the muscles for raising your eyelids. Another really important function of the ocular motor nerve is to control your pupilary response. It causes your pupil to shrink in bright light. This is one of the reasons that doctors might check your pupils. If they don't shrink when exposed to bright light like they're supposed to, this tells us that something is wrong at a very fundamental brain level. Now, together with the abducins, the oculum motor nerve also controls looking side to side. Ocula motor control the oculum motor controls the muscles that move your eye inward like if you're crossing your eyes. And the abducent handles the lateral rectus which moves your eyes outward. So we've got an up down and left right movement of the eye. What else is there? We have another oculum motor muscle the inferior oblique as well as the superior oblique which is controlled by the tlear nerve. What do these do? Ready to be weirded out? They make your eyeball twist. They make it rotate so that you continue to see the world right side up even when you tilt your head. So try this. Look straight ahead. Head up and down. Look straight ahead. You should see the world normally with up is up and down is down. Now lean way over to one side so that you're practically horizontal or lay down. Now you will see the world sideways. Same thing if you go all the way upside down. Now down is up and up is down. and you feel like an Australian. Now, sit back upright. Instead of leaning all the way over, I want you to just tilt your head to one side like like you're touching your ear to your shoulder. You don't you don't need to go that far. Just tilt it some. Does it look like it did when you leaned over completely sideways? Probably not. It probably just looks like it did when you were sitting upright. And that's because your vestibular system in your ears tells your brain how much you're tilted off of perfectly up and down. As long as you haven't gone too far, the brain automatically compensates for this by making your eyeballs twist so that the top of your eyeball is still facing up. This is called the vestibular ocular reflex and it's what the oblique muscles do. Now side note, you do not need to know for example that the abdusins moves the eye outward and the oculum motor moves it inward or which way the trolear rotates the eyeball. But you should know up down is controlled by ocula motor. Left right is controlled by ocular motor and abducins and rotating is controlled by tlear and ocula motor. We just covered nerves three, four, and six. So, we need to go back and grab cranial nerve five, which is the trigeminal nerve. This nerve is really interesting because it is both sensory and motor, as we'll see with a number of these. It detects touch, pain, and temperature from the face and also controls movements associated with biting, chewing, and swallowing. Dentists spend a lot of time working with and around the trigeminal nerve. Now, whenever possible, dentists try to use more superficial anesthesia, including lidocaine, that just numbs you only where they're working. But if you are particularly sensitive to pain, or if they're having to do a more intense treatment, such as a really deep cavity where they need to numb the entire tooth and root and nerve and everything, they'll often use what is called a nerve block. Nerve blocks are blocking that entire branch of the trigeminal nerve. So, they work really, really well, but it numbs much more of your face and it takes way longer to wear off. So, if you ever have a really deep cavity in the top quite ro top right quadrant of your mouth and you need a nerve block, you'll probably notice that your nose and your lower eyelid end up numb for a few hours as well. Cranial nerve 7 is the facial nerve. It is responsible for controlling all of the muscles responsible for facial expressions. It handles taste information from the front two/irds of the tongue and it stabilizes the stapes bone inside the inner ear. The facial nerve is of clinical significance because dysfunction leads to Bell's palsy. Bell's palsy is a condition in which people experience paralysis of a part or even a whole half of their face due to dysfunction of the facial nerve on that side. This paralysis appears very quickly often within 72 hours. We don't know what causes Bell's palsy though we have seen some things related to infection and inflammation and it can happen at any age. It typically gets better spontaneously with over twothirds of people showing complete recovery within a few weeks or months with absolutely no treatment. Though some people do have really long lasting effects and may never gain control over those muscles in their face again. And we don't have terribly effective treatments for it either. Cranial nerve 8 is the vestibular cclear nerve. Just like the olfactory and optic nerves, this is a primary sensory nerve. Colear branch carries information about sound and hearing because this information comes from the cookia. And the vestibular branch carries vestibular information. Seems kind of intuitive. Specifically, this information that helps you with balance and provides your the your head is tilted this much. Information that is necessary for that vestibular cclear reflex that we talked about earlier when we were talking about the eyeballs twisting. Next is cranial nerve 9, the glossoparangal nerve. This nerve detects sensation at the back of the tongue and the back of the throat. This includes taste for the back one-third of the tongue as well as physical stimulation that can trigger a gag reflex or a swallow reflex. The glossoparangal nerve also stimulates the parotted gland which is the largest of your salivary glands. Next, we have arguably the most important of your cranial nerves or at least a nerve that has le has the most wide ranging direct effects which is the vagus nerve. This is also sometimes referred to as the pumogastric nerve. So, pumo referring to lungs, gastric referring to um digest digestive system. The name vagus comes from the Latin word meaning wandering. This is particularly fitting given that the nerve wanders throughout the body directly innervating organs from the brain stem to the colon. The vagus nerve is responsible for all of your parasympathetic needs. It directly intervates all of the organs affected by the parasympathetic nervous system. You can directly observe the effects of the vagus nerve if you see someone pass out while giving blood or from standing for too long with their knees locked back. This can cause vaso veagal syncopy which is where the vagus nerve is activated incorrectly. This causes your parasympathetic nervous system to take over way too much makes your heart rate and your blood pressure drop. This results in insufficient blood flow blood flow to the brain and you pass out. Most of the time once the person is laying down either voluntarily or involuntarily it the drop in blood pressure is no longer an issue and they come back. You can also bring people back quickly by stimulating the sympathetic nervous system using cold compresses or but by putting smelling salts under their nose, which basically is just making them smell ammonia, which your body has a very innate strong reaction to because it smells gross. There's some other tricks that you can use that basically come down to preventing the loss of blood flow to the brain or keeping the sympathetic nervous system active. But really the best treatment for vasovangal syncopy is just avoiding whatever it is that makes you pass out. Cranial nerve 11 is the accessory nerve. It intervates the muscles in your neck and your shoulders that let you turn your head and shrug your shoulders. pretty straightforward, nothing too exciting, so I'm not going to say anything more about it. And finally is cranial nerve 12 or the hypoglossal nerve. Hypoglossal means literally under the tongue and this is because the nerve comes out from underneath the tongue to meet up with those muscles. It controls a lot of your tongue movements. You can see in the picture here a person who has a tongue cramp because the hypoglossal nerve is incorrectly stimulating that muscle excessively. So that's all of your cranial nerves. I have here a couple pneumonics that are supposed to help with remembering which names goes with which names go with which numbers and whether they're sensory or motor. I I really don't care about all of that. Uh there will probably be a couple questions on the exam about what the functions are, what the functions are of different cranial nerves or there might be a question asking you to match the cranial nerve with the function. But I will give you the name and the number. For example, I might list the nerves like they are here, but also add the number next to it so you don't have to worry that I'm trying to trick you into mixing up two nerves or something. So, Vegas would would have an X next to it like that. An X. I'm trying to do this with my pad. It would have an X. All factory would have a one. There we go. A one. And would have a two and so on. This is really hard for me to um that way. If you remember that nerves 3, four, and six are eye movement, but you can't remember what the names were of 3, four, and six, or you remember that vagus was parasympathetic activation, but you can't remember that Vegas is the 10th cranial nerve. No guessing, no dumb memorization that has no purpose necessary. Just make sure that you know the numbers andor the names and what they are responsible for doing.