third and final lecture video on sensory Pathways and nerves here in the peripheral nervous system in AP1 so going into cranial nerves since we've talked about already about the spinal nerves and sort of the idea with how those work as far as their function and linking the rest of the nervous system the peripheral nervous system to the brain they're really kind of a go-between they're not really Central or peripheral at least in my mind they're sort of go between between the two other nervous systems anyway but beyond that we need to talk about cranial nerves all right so what we're going to do is we're going to go through the 12 different cranial nerves we're going to talk about what they're called we're going to talk about what they do we're going to talk about where they go more or less and then we're also going to see what kinds of tests uh might be performed in a doctor's office to see if somebody has fully functional cranial nerves or if perhaps there's been damage to them of some kind um once we're done with that we're going to talk about a couple of mnemonic devices that are going to hopefully help us to remember the names of the cranial nerves as well as their modalities or their functions okay so cranial nerve number one starting with that one is the olfactory nerve all right this one is a unique in some very important ways as we'll see but the olfactory nerve is the first one cranial nerve number one um the other thing I forgot to mention about this is that the cranial nerves are named by their Roman numerals traditionally so it's really helpful if you can remember that uh cranial nerve number one is olfactory without having to look it up um so that's you know you'll kind of hear both being used in various discussions in the clinical setting green number 10 vagus nerve whatever um you'll hear both so you really need to be able to understand and kind of translate between the two all right so cranial cranial nerve number one is a sensory only cranial nerve and if you think about that for a minute um there really isn't much need for information coming from the brain to reach olfactory receptors in the nose so it kind of makes sense that this one is just a sensory cranial nerve there really is not a motor function associated with this one at all it's only sensory um so this one is going to be routed through um again through the cranial nerve information to the telencephalin specifically the um the thalamus will be where it's routed the test for this one coffee grounds is fairly common I believe anything that has kind of like a unique smell to it that almost anybody should be able to identify if they're olfactory receptors are functioning properly um if they're unable to identify or even detect the smell of something like coffee grounds then you might suspect damage to cranial nerve number one for example okay cranial nerve number two is the optic nerve this one is also sensory and this is the primary nerve that is associated with vision all right the the other nerves associated with the eyes are going to be nerves carrying information from the brain to the eyes as opposed information coming from the eyes going to the brain this is the one that's doing the ladder this is the one that's carrying information from the eyes to the brain where it can be processed and identified and associated with some type of image perhaps we have past experience with right so this one also is sensory only this one is going to be routed to the diencephalin so I will process that in in the um occipital lobe of the brain and with this one various tests charts um the basic kind of color blindness tests you might see at a doctor's office peripheral vision tests all of those kinds of things are going to help us to determine whether cranial nerve number two is functional the next several with the exception of one are going to all involve the eyes as well but they're going to be more on the motor side of things okay so this is now the first one that we've seen that has a motor function as its modality this one the oculomotor uh cranial nerve number three is going to associate with a midbrain the test with this one is to be able to follow the object and the main thing I want you to remember with all of the cranial nerves associated with motor function with the eyes is not specifically what the cranial nerves allow the eyes to do as far as like which direction they move so in other words if they move up and down or if they move side to side or if they whatever um the the muscles that make your eyes move in your head are very specific and very very uh uh small um so I'm not so worried that you know which muscles are innervated by cranial nerve number three or any of the rest that are motor I just kind of want you to know what they do and that means physically allowing the eyes to move around in the sockets to allow you to see as far as which cranial nerves go with which muscles uh I'm not going to be too hung up on that right now okay so I just want to make that clear all right cranial nerve number four the trochlear nerve is also a motor nerve associated with the eyes again different set of muscles also goes to the midbrain you can also use the follow the object test very similar in terms of basic modality and function as well as Association as the ocular motor all right so three and four as we're going to see number six is going to be the other one that goes along with the eyes but for right now we're going to take a quick detour and take a look at creating alert number five so cranial nerve number five is a little special because this is the first one that we have seen that has a mixed function so in other words if you were to take the trigeminal nerve and dissect it in half cut it in half make a cross section of it what you would find is that some of the axons that we're making up the nerve represent motor neuron axons and some of the axons in the nerve represent sensory neuron axons okay so this one has information going in both directions from the face to the brain from the brain to the face going in both directions okay so this one is a mixed nerve this one has both motor and sensory function and its associations with the pons with this one the the basic functions on this one would be if you can chew properly because that's motor function and then also uh you know touching the face closing your eyes and touching your face on a certain location or closing your eyes and detecting whether something is touching your face those are the kinds of things you might associate with cranial nerve number five cranial nerve six like I said a moment ago is the third and final of the cranial nerves associated with the movement of the eyes this one also goes to The Ponds unlike the other two but it also has the same test in terms of following the object so any of these three cranial nerves uh affect movement of eyes so you kind of get a sense for how much of a visual species we are because we have what four of the 12 cranial nerves that are just associated with vision three of them are for movement one of this for sensory that kind of hints at the fact that our eyes are pretty important to us as a species okay facial nerve is the next one this is number seven a lot of the rest of the ones are going to be mixed uh this one goes to The Ponds as well this one again is is sensory is fairly straightforward to sort of tactile sensory feeling on the face but the ability to make funny faces if you can't do that it suggests that cranial nib number seven has been disrupted in some way or it's been affected in some way because if that nerve cannot make the muscles in the face fire the way they're supposed to or the way you want them to then communication has been interrupted in some way it's kind of sad that way cranial nerve number eight used to be called the auditory nerve I don't think it's called that much anymore it's now referred to more so as the vestibular cochlear nerve which is a much more Awkward name to say and spell uh but this one is sensory this one goes to The Ponds as well as the medulla and this one is the one most associated with both hearing as well as balance okay so the reason why cochlear refers to the ear cochlear is the the hearing aspect of the vestibulocochlear nerve and again we have a sense here a like a a sensory detection of the environment of hearing which is pretty important but again this one only has one cranial nerve associated with it and it's for sensory only it's kind of like how the nose was olfaction was one one cranial nerve one function sensory only auditory is the same way but then again our eyes had four so that lets you know kind of even if you weren't human which of our senses is most important to us just by seeing how many cranial nerves are associated with our vision cranial nerve number nine is the glossopharyngeal nerve which is again a mixed nerve this one routes information to and from the medulla this one's primary test is uh sensory test of gagging or tasting uh substances that you should be able to taste the definitive tasting things um sort of like the coffee grounds test for olfaction you would have some type of um fairly distinctive taste that you would then offer to someone and if they can detect it then things are working properly and if they can't or if it's the wrong perception then you know something's wrong with cranial nerve 9. um the gagging is the motor function so the glossopharyngeal nerve is very much involved with all the various muscles that help to squeeze food down your esophagus say it that way it's sort of the best representation of it uh so if this nerve is not firing properly if you were to try to induce the gag reflex and nothing happened then you would suspect again some sort of damage to cranial nerve 9. cranial nerve 10 is a big one in terms of function um this is probably of all of these I would say that the most important one for your money to remember is cranial nerve 10. this is a mixed nerve information goes to the medulla this one is involved with just about every other visceral function in our body that we have not mentioned yet okay so if it's not uh if it's not olfaction if it's not your eyes if it's not your face if it's not your hearing or you're swallowing slash tasting reflex and that's where cranial uh the last couple are going to show up as well then it's going to be vagal Nerf or vagus nerve function or vagal nerve function um because it's it sort of has the most functionality throughout the rest of the body so if we're talking about you know digestive system function that one is vagus nerve control okay so again you can do a gag test for this one that's also motor uh here as well you can also do if someone's having trouble vocalizing like if they're if they're unable to physically speak if they're forming words in their mind if they can understand words if they could write it out on paper but they can't physically make the sounds that could also implicate uh malfunctioning of the vagal nerve so that one's a very very important one to remember spinal accessory nerve is is one of the really I think one of the more minor ones um this one is a motor neuron only again sending information to the medulla or sorry from the medulla to the motor neurons in the shoulders which allow you to shrug your shoulders okay so the best explanation for this one that I have is that right so like everything below the shoulders is innervated by spinal nerves to some degree everything from the shoulders and the face I guess we'll say shoulders and face are innervated by cranial nerves right everything else so that the top of your head the back of your head um your back your neck uh all of that stuff is innervated by um cranial nerves but from like your muscles that move your shoulders down that is all spinal nerves okay so think about it kind of as far as division that way the last one is the hypoglossal nerve which is cranial nerve 12. this one's also motor only this one is associated with muscles that allow you to move your tongue which your tongue actually does need a fair amount of motor control because it has a lot of musculature and a lot of ability for very fine movements to allow you to talk and speak but also to chew your food obviously as well so that one gets its own cranial nerve but this one's also motor only okay so those are the 12 cranial nerves um notice up here at the top we have this uh this list of abbreviations that correspond to the first letter in each of the names of the cranial nerves all right so the the one that I talk about in class is uh the G-rated one right so this one is uh on Old Olympus towering tops of Finn and German viewed some hops