Advanced Assessment of the Cranial Nerves VIII–XII

00:01 Next up, we'll do the 8th cranial nerve, which is the vestibulocochlear nerve.

00:05 Now this has two components the vestibular component and the cochlear component.

00:09 And we're going to do the latter part first.

00:11 Grossly, we just want to assess hearing by simply the finger rubbing test.

00:16 So I'm just going to do this, can you hear this on both sides? Quick way to establish that the person does not have any gross hearing loss.

00:23 If there was any asymmetry when we did that simple maneuver, or if the patient's reporting the problem with hearing, we would then move on to perform the Weber and Rinne tests with a tuning fork.

00:35 Ideally, you want to use a 512, you could also use a 256.

00:39 Patients who are older oftentimes will lose the ability to hear higher pitches like a 512.

00:45 And that's sort of a normal part of aging is presbycusis that loss of those very high pitches.

00:51 Both of these tests are designed to distinguish between conductive hearing loss versus sensory neural hearing loss.

00:59 And conductive hearing loss would be if he even had a lot of wax in his ears that was occluding the external acoustic meatus than the sound that I make out here is simply not going to get to the eardrum, or if there's a problem with the perforated eardrum or if there's a problem with the ossicles of the bones that are magnifying the sound and transferring it or passing it on to the sensory nerve to the cochlear nerve.

01:22 So conductive hearing loss versus sensorineural hearing loss that's what we use these these tests for.

01:28 I always remember which one of these tests is the Weber.

01:31 The Weber test is going to be up here.

01:33 Weber starts with a W, and that's a symmetric letter.

01:36 And so I can remember I'm starting in the middle of his forehead.

01:38 And we'll do that now by making a loud sound.

01:43 Which side do you hear that, the most on or is it pretty much the same? A little harder.

01:48 Sure.

01:53 Both.

01:54 Great.

01:54 So if you had a problem with conductive hearing loss, again, let's say that his left ear was completely full of cerumen and he was unable to get any sound moving to his sensory nerve, his cochlear nerve, his cochlear nerve on the left would be starving for information, and so would amplify its sensitivity to sound.

02:14 And so when I put this on his forehead, he would lateralized to the left, if he had a conductive hearing problem, he would try and his left cochlear would be amplifying its detection of sound, even though it's vibrating through his skull.

02:28 In contrast, if he had a sensory neural problem, let's say on the left, where the nerve was out, perhaps due to like a schwannoma, or a viral labyrinthitis, something that's causing damage to the nerve itself, then when I put this on his forehead, he would lateralize to the right, because the left sensory input is not functioning, the detector is not functioning.

02:51 So this test doesn't tell us what the cause of the problem is, because you need to do the next step in this test.

02:57 And that's the Rinne exam.

02:59 The Rinne exam is performed as follows.

03:04 Can you hear that? Yes.

03:06 Let me know when you stop hearing it.

03:22 Stop.

03:23 Can you hear it now? Yes.

03:25 Great.

03:26 So what we've done there is we've used his mastoid process, which is where I've put the head of this tuning fork to test for bone conduction.

03:37 Bone conduction is essentially seeing if the sensory nerve is still able to gather information.

03:42 Whereas when I hold the tuning fork out here, this is air conduction, which relies upon the, again the machinery of hearing.

03:52 If, under normal circumstances, air conduction should be better than bone conduction.

03:59 Because in general, the ears were designed to magnify information coming from sound.

04:05 And that's what the ossicles and dependent membrane they're designed to do, as opposed to getting sound just from vibrations on your skull, which is what I'm testing with bone conduction.

04:14 So again, if his ear is full of cerumen, he's going to have decreased air conduction, because the sound of vibrations from the air is just not going to penetrate past there.

04:25 So when I did this test, and waited till he could no longer hear via bone conduction, when I would bring the tuning fork out here, he would not have been able to hear it.

04:33 And then I would know, especially if the Weber test had localized to the left side that his problem is a conductive hearing loss problem.

04:41 So those are the two tests that we use to really dive in and identify conductive versus sensorineural hearing loss.

04:49 All right, with that we can move on to Cranial Nerves IX and X.

04:53 So cranial nerve IX is the glossopharyngeal nerve, cranial nerve X is the vagus nerve and we're going to do them together.

05:00 The vagus nerve has a lot of other things that it does in terms of the autonomic nervous system.

05:05 But for the purposes of the bedside physical exam, we're really focusing on its role in terms of regulating swallowing.

05:12 So these different nerves are difficult to distinguish their actions when we're looking at the swallow reflex.

05:19 But they are going to help us, we can identify that they're both out or not using these maneuvers.

05:24 So let me first grab my pen light, my otoscope light.

05:29 So the glossopharyngeal and vagus nerves are going to help with elevation of the soft palate.

05:34 So let's take a look.

05:36 Say 'ah'.

05:37 Ah.

05:38 Great, we can see that there's symmetry between the arches and the back there is soft palates going up, we also see that his uvula is also midline.

05:46 In a patient for whom there was evidence of a symmetry and one side is not going up the way that it should.

05:51 We could then test the gag reflex, which you can either do with a Q-tip swab and just touch the back of the throat or tickle the uvula to make sure that the gag reflex is intact.

06:02 All right, we're on the homestretch with the cranial nerve exam, we're on cranial nerve XI.

06:06 This is the accessory nerve.

06:07 And this nerve innervates two important muscles, and it's the sternocleidomastoid and the trapezius muscles.

06:13 To test those, I'm just going to have you turn your head to the left against resistance.

06:18 Great.

06:18 And keep in mind that him turning his head to the left is actually the function of his right sternocleidomastoid muscle which you could see was tensing up there, and then I'll have you turn your head to the right.

06:29 Great and that's his left sternocleidomastoid muscle shown there, and then the muscles of the trapezius are operating to lift his head is elevate his head, or laterally flex his head as well depending upon the orientation of his head at the time.

06:43 So next up is the 12th cranial nerve, the last one, this is the hypoglossal nerve and it's simply tested by having the patient stick your tongue out please and move it from side to side.

06:53 Put your tongue back.

06:54 A patient who has a defect in the 12th cranial nerve on the left will actually deviate their tongue towards the affected side because that nerve is designed to make the tongue muscle pushed out.

07:06 So if it's not working, it's going to end up being dominated by the right hypoglossal nerve and the musculature which will push the tongue off to the off to the left.