Health Assessment, part 27: Cranial Nerve VIII - Vestibulocochlear/Acoustic

Hi. I'm Meris, and in this video, I'm going to be reviewing the type, function, and assessment of cranial nerve 8, vestibulocochlear or acoustic, depending on how you know it. I'm going to be following along using our health assessment flashcards. These are available on our website, leveluprn.com, if you want to get a set for yourself. Or if you would prefer the digital version, you can check out Flashables. We have a digital version of all of our flashcards that are available for you right now on that same website. All right. Let's go ahead and get started.

So first up, let's review the type and function of cranial nerve 8. Now, you will hear this nerve referred to as either vestibulocochlear or acoustic, depending on the source you use, your professor, your school. So either one is correct, but you may hear me refer to this as the vestibulocochlear nerve because that is how I know it best. Okay. So this is a sensory nerve, and its function is that it is responsible for hearing and balance. So the vestibular sense-- this is why I like vestibulocochlear as the name. The vestibular sense has to do with one sense of balance, one sense of position in space, and then cochlear, of course, referring to the cochlea of the ear, which is responsible for hearing. So that is the type and function of this nerve.

So how do we assess it? Well, we've got three different tests that we can use to assess the function of this nerve. First up is the whisper test. And luckily, it is what it sounds like. It's a test that involves whispering. So what this means is that while shielding your lips, meaning that your patient cannot see your lips, right? This is what football coaches do when they're on TV. They cover their mouths so you can't read their lips. So same idea. We don't want our patient to be able to see what we are saying. We're going to cover our lips and whisper three random letters or numbers from one to two feet away and ask the patient to repeat them. So what does this look like? It would look like if I'm shielding away from you, right, I would say like, "5, C, X," from one to two feet away. And I would hope that my patient would repeat 5, C, X. I'm going to then move to the other side, and I will repeat that process to see if my patient is able to hear at that soft, quiet tone, if they are able to hear what is being whispered to them.

So next up, we're going to talk about some different tests that use a tuning fork. And if you've never seen it, a tuning fork is a piece of medical equipment that one would strike against their hand. You hold it by the centerpiece, and then there's the two prongs that come up. You hold the centerpiece, strike the two prongs against your hand, and it's going to begin vibrating at a specific frequency that produces a pitch. Now, we can use that tuning fork to assess the vestibulocochlear nerve in two different ways. The first is going to be with Rinne test. So Rinne test is where we are going to be testing to see if our patient has better air conduction or bone conduction of sound.

So what does that mean? Well, right now, if you are listening to me through speakers or through headphones that sit in your ears, you are listening to me primarily with air conduction. The air is conducting the sound all the way to your ears. However, we can also hear with bone conduction. And this is why, right now, I hear myself talking, but it sounds very different than if I were to record this and play it back. My voice will sound different to me because I am hearing my voice currently both through bone conduction and air conduction. I'm hearing it conducted through the air and back around to my ears, but I'm also hearing my voice transmitted through the bones of my skull, which changes how that is sounding to me. We expect our patients to be able to hear with both air and bone conduction, and we expect that air conduction should be greater than bone conduction. They should be able to hear better when it is conducted through the air than through the bone.

So with Rinne's test, we're going to strike that tuning fork, and I'm going to initially place that middle stem right on the mastoid bone, right here behind the ear. And I'm going to place it directly on the ear. And I'm going to ask my patient to let me know when they no longer hear the sound conducted from that point. When my patient no longer hears it, I will then take that same tuning fork that I've been holding here and I'm going to not strike it again. It's still vibrating. I'm going to now move it in front of my patient's ear and see if they can still hear the vibrations. We expect that they will no longer hear the vibrations with bone conduction. I move it in front of their ear, and they should begin to hear it again with air conduction. The expected finding is that air conduction would be greater than bone conduction. An unexpected finding would be that if my patient says, "Okay. I don't hear it anymore," and I move it in front of their ear, that they say, "I don't hear it anymore." There's many reasons this could be. This could be due to a blockage. Perhaps they have a wax impaction in their ear where all the ear wax has gotten pushed up against the tympanic membrane. There's many different reasons that this could be, but that would be an abnormal or an unexpected finding.

Now, we can use that same tuning fork to assess a different type of hearing with the Weber test. So the Weber test, we're going to, again, strike that tuning fork. And instead of placing it on the mastoid process, we're going to place it directly on the center of the head right in the midline. And what we expect is that our patient should be able to hear, through bone conduction, the same volume, the same intensity of that sound on the right versus the left. Now, if I put that tuning fork on top of their head, and they don't hear it at all, or they hear it only in one ear versus the other, or if they hear it stronger in one ear versus the other, those would all be abnormal findings. This is not a specific cool chicken hint that we have. This is just a way that I remember this. But to remember the difference between the two, I always think of Weber is a test, but it's also the name of a grill. And it's a grill that has a very classic domed appearance. And so I think of this domed appearance as it is like a person's head. So I think about the Weber test as putting it on the grill, on the head, versus the Rinne test is going to be placed back here on the mastoid process.

All right. So that is it for our review of cranial nerve 8, vestibulocochlear or acoustic. Now I hope that you will stay and test your knowledge of key facts I provided in this video using these quiz questions. Where should the nurse place the tuning fork when performing the Weber test? On top of the patient's head. Where should the nurse initially place the tuning fork during the Rinne test? On the mastoid bone. How far should the nurse be from the patient when performing the whisper test? One to two feet. Does the nurse expect the patient's air conduction or bone conduction to be greater? Air conduction.

All right. That is it for this video. I hope it was a useful review and that you learned something. It would mean a lot to me if you would leave a comment. Let me know something you learned or something you liked about this video. I always read those comments, and I know that other students reading them can benefit if there's something that you have found as a way to remember content in this video as well. Thanks so much, and happy studying.