Health Assessment, part 25: Cranial Nerve IV - Trochlear & Cranial Nerve V - Trigeminal

Hi. I'm Meris, and in this video, I'm going to be reviewing with you the type, function, and assessment of cranial nerve 4, trochlear, and cranial nerve 5, trigeminal. 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 hard copy for yourself. Or if you prefer digital flashcards, I would invite you to check these out with Flashables, which are our digital version of these flashcards. All right. Let's go ahead and get started.

So first up, we are talking about cranial nerve number 4, trochlear. So this is a motor neuron, and it controls downward, outward, and inward movement of the eyes. So when we assess the trochlear nerve, we are actually going to be assessing it at the same time as cranial nerve 3, oculomotor. Remember that cranial nerve 3, 4, and 6 make your eyes do tricks. So 3, 4, and 6 are assessed together because they are all responsible for movement of the eyes. So therefore, the assessments all go together. When you are assessing cranial nerve 3, you're also assessing 4 and 6.

All right. Moving on to cranial nerve number 5, trigeminal. So this is both a sensory and a motor nerve. This is a mixed nerve, and this one is responsible for facial sensation and chewing. So we've got two functions. That means that we need to assess it in different ways. We need to assess the sensory and the motor component of this nerve. So how do we do that? Well, with the sensory component of this, the best way that we can do this is we have our patient close their eyes, and then take something like a cotton ball or a cotton wisp, you may hear it called, and we are going to lightly touch it to the patient's face in some different areas and ask them to identify where they are feeling the sensation of light touch. That's going to be how we can assess the sensory component of cranial nerve 5.

Now, we can also test the corneal reflex by moving a cotton wisp towards the cornea. So this is not something that we are necessarily going to do all the time for every patient. However, this is commonly done when we are assessing the neurological status of patients who might be experiencing brain death. But certainly, it can be assessed on other patients as well. So what the corneal reflex is, it's the blink reflex. It's the idea that as you bring something up to my cornea, as you touch my cornea, or I feel like you're about to, I should blink my eye. So we can take that cotton wisp, bring it up to the patient's eye, and touch or attempt to touch the cornea. And the expected finding would be that they blink. And then, of course, the motor component of the trigeminal nerve is going to be assessed best by palpating for strong and equal contraction of the temporal and masseter muscles.

So what does this mean? This means that I'm going to place both of my hands on my patient's temporal muscle, so right here at the temple, and ask them to clench their jaw. So I'll say, "Okay. Go ahead and clench your jaw for me." And we should feel strong and equal contractions on both sides when the patient clenches their jaw. We can also feel the masseter muscle. Mastication is chewing. So the masseter muscle is the one that helps with chewing, and it's this one right here. So again, I can place my fingers on either side and ask my patient to bite down, to clench their jaw. And I should feel strong and equal contractions of the masseter on either side. All right. So that is it for the assessment of cranial nerve 4, trochlear, and cranial nerve 5, trigeminal.

I'm going to ask you some quiz questions to test your knowledge of some key facts I provided in this video. Which eye movements are controlled by cranial nerve 4? Downward, outward, and inward eye movements. How should the nurse assess a patient's corneal reflex? Lightly touch the cornea with a cotton wisp and observe a blink. How can the nurse assess the sensory function of cranial nerve 5? Test sensation over several areas of the face using a cotton wisp with the patient's eyes closed. All right. That is it for this video. Thank you so much for joining me. I hope it was helpful. Thank you so much, and happy studying.

So when I was a kid, my favorite magic trick that I used to do was where I-- you have to have a partner for this. So I would do this with my parents or a friend or something like that. And I would say that I could read minds. And I would come up behind my partner, and I would place my hands on their temples, right? And I would say, "I want you to think of a number." And they would close their eyes and think of a number. And I would say, "Okay. Do you have the number?" They would say, "Yes." And I would say, "Okay. I want you to really, really think about it, and I'm going to try and read your mind." And while I had my hands here on their temples, they would bite down, right? They would have their mouths closed. And let's say it was three, they would just very, very lightly go-- and I could feel the contractions of the temporal muscle. And so then I would say, "Oh, this is a tough one, but I think your number was three." And they would say, "Oh, my gosh," whatever. And I remember thinking that that was just so cool that I was probably six or seven years old when I was doing this. But what I didn't know that I was actually assessing cranial nerve 5. Pretty cool.