12 Cranial Nerves: Anatomy & Physiology

[00:00] Alright everybody, Mr. J here from Organized Biology. You're learning about the cranial nerves today. There are 12 of them. They have wacky names, a lot of different functions, but I realized that. So therefore, I've made some helpful mnemonics to help you out. And as we go through this lesson, I'm going to give you helpful tips and tricks to help you memorize them easily so you can

[00:20] can ace your test and then hopefully use them clinically. So let's get started first. Cranial nerves, when you look at the word nerve, we've probably heard of spinal nerves before. Basically these tracks of axons running in and out of these tubes called nerves. Now in the cranial nerves, what's interesting about them is they can carry

[00:40] either sensory information, they can carry motor output, or they can carry both. Now that is contrasted to the spinal nerves because the spinal nerves always have both, but for the cranial nerves they might be one or the other or both. Now how do we know that? Well I want you to remember the mnemonic.

[01:00] Some say merry money, but my brother says big brains matter most. Kind of a clever little saying. Now if you look at the first letter of each word, what do you notice? Well, they correspond with either S-M or B, S-M or B. So if you put that in order of the cranial

[01:20] nerves 1 through 12 in order, Roman numerals, you will have each of those functions. So for example, for cranial nerve number 1, it will associate with the S, meaning that it will only carry sensory information. The second one, the same thing. So I'm going to finish this out. Sensory-sensory, motor-motor, both, motor-numerals.

[01:40] Both, sensory, both, both, motor, motor. That will be really helpful for you to remember. Now we got the numbers, we got what they do. But what about the names? Well, I'm glad you asked. We've got another new monic here, 000 to touch and feel very great.

[02:00] Velvets are heaven. Oh, it's touch and feel very great. Velvets are heaven. Again, the first letter of each one is going to correspond to each of the 12 cranial nerves, first letter of the name. So how do we name the cranial nerves? Well here we get the brain on an inferior section. We're looking up at the brain. Here's the front and here's the back and the surface.

[02:20] spinal cords right there. And as you can see, we're kind of moving from anterior to posterior. In fact, that's how the cranial nerves were actually named, was basically where they appeared from front to back. So we're going to move through these 1 through 12 and name them. And I'm going to give you once again some helpful tips and tricks on why these are here.

[02:40] they named them the way they did. So the first one here, we've got cranial nerve number one. This is going to be the olfactory nerve, olfactory nerve. Now olfactory refers to the sense of smell, and the reason for that I think is if you were to be blindfolded and walk into an old factory, the first thing you would notice

[03:00] This is the smell. So olfactory kind of means smell. The second one here, we've got cranial nerve number number two. This is going to be the optic nerve, optic nerve. If you've ever heard of an optical illusion, it's some sort of a visual illusion. So this is going to deal with vision, of course.

[03:20] All right, moving on to cranial nerve number three here, once again another O, this is going to be the oculomotor nerve. Oculomotor literally translates to eye movement. So this is gonna be a nerve talk to the eye muscles, helping them move around. The fourth one here, we've got the trochlear nerve. It's our first T rather than an O.

[03:40] We have trochlear, a weird name. Trochlea means pulley, like a pulley system. There is actually a pulley system in your eye for a specific muscle that will pull that eye down and out. We will talk about that in a second. The fifth cranial nerve here looks kind of interesting. We have these three branches on it. We called it the ileusis.

[04:00] trigeminal nerve, trigeminal, because tri refers to three. And gemina or gemina means twin. Like gemina is like a horoscope thing I think and they're the twins, right? So three twins. The sixth cranial nerve, we keep moving through through here. We've got an A here.

[04:20] So, the cranial nerve number six is going to be the abducens nerve. Abducens nerve kind of sounds like the word abduct. It's actually going to abduct the eye. Cranial nerve number seven we've got here is going to be an F as you can move through it and see. This is going to be the facial nerve. This one's going to be the facial nerve.

[04:40] kind of tells you where it's at, it's going to do a lot of things before the face, so we'll get to that in a second. Cranial nerve number eight, we're getting down to it. Cranial nerve number eight, big long words, vestibulocochlear. Vestibulocochlear. And this is straight up saying the two structures involved here,

[05:00] vestibule in the inner ear as well as the cochlea in the inner ear. So it's attached to those two structures we'll talk about in a second. Cranial nerve number 9 after that V is the G for glossopharyngeal. You may see a trend here, glossopharyngeal. All of these names are corresponding to structures where

[05:20] within themselves, right, like what they're talking to. So glosso always refers to tongue and the pharynx is your throat. So it's like the tongue throat nerve. It's gonna talk to the tongue throat, wonderful. Cranial nerve number 10, this one's a fun one. This is the vagus nerve and vagus, I like it.

[05:40] like to translate to wanderer. The reason I kind of laugh at this one is because vagus sounds like the word Las Vegas where there are a lot of wandering souls. So this nerve wanders about and goes to a variety of different structures in the body. Caraneal nerve number 11.

[06:00] Getting down to it, you see that this one's going to start with an A. This is your accessory nerve, accessory nerve. That won't help you too much, but I'll give you a little hint later on. And then finally, cranial nerve number 12, this is going to be your hypoglossal nerve. Where do you think that will be? Well, hypoglossal.

[06:20] glosso means tongue, hypo below the tongue. Brilliant. So those are the 12 names. So I already talked to you about how if we correspond them to their respective functions, we'll know generally what they do. So if I were to ask you, hey, what type of information is the oculomotor nerve carrying? Well you would look

[06:40] back and look at cranial number 3 and see oculomotor is a motor neuron or motor nerve and so it's going to actually talk to structures to change their function. Whereas if I say hey what does the optic nerve do? Well the optic nerve is only going to carry sensory information so that's why this these mnemonics are really really helpful. Now before you go

[07:00] I want to run through the functions because these are usually what you're going to get tested over in a class So let's roll through them real quick all factory cranial nerve number one. This is the primary function of the sense of smell So we're going to detect smells or odors With this nerve and transmit them to the brain. That's a type of sensory information

[07:20] So olfactory is just about detecting odors sending that information to the brain. Second one is the optic nerve and this is going to just be detecting light. So we're detecting light and we're again sending that signal back to the brain about what we are seeing. So if you had damage to the optic nerve, you could probably predict that you will be blind.

[07:40] So if you get damage to the optic nerve, you will go blind. Third one, oculomotor. Once again, I told you what this one does. Oculomotor moves the eye. So I'm going to say specifically somatic motor neurons to move the eye. Now this is going to go into a little bit of the nervous system.

[08:00] somatic means we're talking to the skeletal muscles that you can control. So when you think, oh, I'm going to turn my eyes different places, you're using that oculomotor nerve to move voluntary skeletal muscles. However, we also have some parasympathetic neurons here. I'm going to write parasympathetic.

[08:20] your rest and digest nerves. I'm just going to shorten this up as PS in the future. And these parasympathetic neurons are going to go specifically to the pupillary muscles. Okay, so basically the muscles that will dilate and constrict your pupils as well as

[08:40] muscles, the ciliary muscles dealing with your lens, I'm just going to say lens muscles, and that helps with accommodating your vision. Now think about that. Do you control when you narrow your pupil or constrict your lens? No, that happens automatically. That's because the parasympathetic is a part of the autonomic nervous system which you can learn about.

[09:00] on my channel as well. Let's move on to cranial nerve number four. This is motor trochlear, right? So this is the trochlear nerve. All it does is it helps to move the eye down and out. This is via the superior oblique muscle. Superior oblique muscle.

[09:20] oblique, acts as a little pulley system, pulls your eye down and outward. So if it was like this eye, it would turn it down and out that way. If it was this eye, it would turn it down and out that way. Pretty cool. Alright, so that's somatic motor as well because it's a skeletal muscle. Okay, fifth one, trigeminal. Trigeminal is both, so we've got

[09:40] got our first both cranial nerve and this is going to do a variety of things. It's going to be somatic motor, we can control these things to the muscles of mastication. Mastication means chewing basically. So whenever you're chewing like this, right, you're using that trigeminal nerve talking to these muscles of your

[10:00] masseter specifically and you're mandible and it's going to contract that. Okay we're also going to have some sensory information, sensory from the jaw and mouth as well as the mucosa of the nose. So if you're feeling things like in your in your mouth and your gums and your nose

[10:20] it's going to be basically sent back to the brain via the trigeminal nerve. This is a common site when they inject novacane into your mouth like during a dental operation. They're trying to target branches of your trigeminal nerve because they're trying to numb that up so you don't feel it. That's helpful, right? All right, wonderful. Next one up we've gotten six. That is the abducens nerve.

[10:40] Abducin is just motor and again, it's just going to abduct the eye. So we're going to talk to the abductors of the eye. So it's going to take your right eye and move it outward to the right. Take your left eye and move it outward to the left. Brilliant. Moving on. We've got now cranial nerve number seven, facial nerve. Facial as you can see is bone.

[11:00] So that means we're going to do a couple different things. First off, we're going to make facial expressions with these. That's the reason it was named. So when you make facial expressions, you are basically using muscles of your face to smile, to frown, and that type of thing. Okay, so if you're like furrowing your brow, using that facial

[11:20] expression through the facial nerve. You're also going to get a little bit of taste in the anterior part of tongue. So I'm going to write anterior part of tongue. So primarily sweet flavors. Okay so you can remember kind of like you can give people a sweet facial expression and you can also have a sweet taste through the facial nerve.

[11:40] nerve. It's also going to have a little bit more sensations just on the superficial parts of your face like your skin whereas the trigeminal nerve was deeper parts like in your gums. Brilliant. So I'll just say senses on face. Great. We're moving right along y'all. Number eight, we've got that vestibulocilate

[12:00] This is just sensory because the vestibule, that vestibule part, is going to deal with equilibrium and balance. I'm just going to write balance. So basically keeping your head upright and knowing where you are in space. And then the cochlear part is going to deal with hearing, so sound, and then sending that sound back in.

[12:20] to the brain or sending the transmissions of the signal of sound back to the brain. So the balance part once again is in the vestibule. It's called the vestibular nerve, the branch of it, and then the sound is actually going to be traveling through the cochlea, the cochlear nerve. Cool, all right, let's keep moving forward. So we've got cranial nerve number 9 now is

[12:40] Both are glossopharyngeal. Glossopharyngeal is an interesting one. It implies that it's just like the tongue throat, but it actually does a couple other things. Let me talk to you about that. Let's talk sensory first. Sensory is going to detect a variety of different tastes in the back two-thirds of your tongue. You're also going to have some motor output.

[13:00] to the tongue as well as to the throat as you can guess for swallowing. That's a very important function. And then also with sensory but you don't detect it, it's also going to detect some chemo receptors on the carotid artery. Chemo receptors on carotid artery.

[13:20] carotid artery. Now do you detect this like consciously? No, but these chemo receptors basically detect pH of your blood, feed it back to your brainstem. As you can see, most of these originate in the brainstem and it's going to basically tell the autonomic nervous system, hey, we need to like breathe a little faster or hey, we need to feed it back.

[13:40] our heart a little faster to get this pH regulated. So that's an interesting one. It also will have some parasympathetic innervation. So I'm going to write parasympathetic and it's going to specifically go to the salivary glands and it's going to stimulate those salivary glands. If I can spell gland right.

[14:00] stimulate them to produce saliva which makes sense and I realize now cranial nerve number 9, I forgot cranial nerve number 7 in the facial nerve will also have some parasympathetic that will also go to the salivary glands as well as the lacrimal glands which basically produce your tears.

[14:20] your tear ducts. Alright, brilliant. So sorry I forgot about that already. Moving through, we've got now to vagus nerve number 10, the wanderer. It goes everywhere. Golly gee, I'm going to start with sensory. I'm going to say it's sensory to basically all the viscera or internal organs like your heart, like your intestines.

[14:40] etc. It also has some sensory to your throat. Your respiratory tract of vagus nerve basically travels everywhere throughout the internal organs, detecting what's going on down there. Now it also will have some motor output, motor function, specifically to some parts of the throat.

[15:00] for speaking, so like the larynx. And you're also going to have parasympathetic from the vagus as well, so parasympathetic. Basically all internal organs, besides like the bladder and the genitals, will be controlled parasympathetic.

[15:20] speaking if we're talking about like the intestines we're going to stimulate them. But if we're talking to the heart we're actually going to slow down the heart with the parasympathetic because parasympathetic deals with resting and digesting. So the brainstem with the parasympathetic is generally calming you down which is a good thing. Okay so I'm going to move forward from the vagus nerve, cranial nerve number 11.

[15:40] That is going to be our accessory nerve. Now I want to tell you a story for this quick so you can remember. If you are an accessory for murder, you stick your neck out for somebody, don't you? So say you're like in the getaway car and like a person robs a bank and you get them in your car and you drive away, you're an accessory to murder if they murdered somebody in the bank. So I think you stick your neck out for murder.

[16:00] your neck out for somebody, you are an accessory because the accessory nerve primarily helps you move the neck as well as shrug your shoulders. So that's somatic motor to those skeletal muscles. Alright your last one here this is the hypoglossal it's just motor and all it will do is

[16:20] is just move a little bit of your tongue. So we're going to say move tongue, primarily to help with speech and a little bit of swallowing. So that is it. This is the cranial nerves overview. Hopefully this was helpful. If you have any questions, drop them in the comments below. Like the video, subscribe to the channel. I appreciate you watching and I hope this was helpful.