Okay, let's talk about facial palsy and stroke and answer the what questions. What role does the facial nerve play in facial expression? And what is facial palsy and how does it happen? And what effect does a stroke have on facial expression? Hello everyone, my name is Dr. Morton and I'm the Noted Anatomist.
Okay, so lower motor neurons of the facial nerve innervate ipsilateral facial muscles. What does that mean? Well, here's the lateral picture of the head, and there's the pons, which gives rise to the facial nerve, which traverses the internal acoustic meatus and then gives rise to a branch called the facial nerve proper, which descends in the facial canal of the temporal bone.
And so the course into the axon exits the stylomastoid foramen, which is not shown in this picture, and that facial nerve proper continues through the parotid gland. and then gives rise to five branches that innervate muscles of facial expression. And those muscles include the frontalis muscle that wrinkles your forehead, and orbicularis oculi that closes your eye, and nasalis muscle that flares your nostrils, and zygomaticus muscles which make you smile, and orbicularis oris muscles that help you close your mouth and pucker your lips.
The facial nerve does not innervate the temporalis or masseter muscles, which are muscles of mastication. And they are not innervated by facial nerve, but they are innervated by the mandibular branch of the trigeminal nerve. So, let's do this again in this picture.
In this coronal section at the top, we can see the pons, and the pons contains the facial nucleus. And the facial nucleus is all nuclei or a collection of cell bodies. Some of those cell bodies give rise to lower motor neurons that innervate the forehead muscles, and some Lower motor neurons give rise to axons that innervate muscles of the lower face, like this. And this occurs bilaterally. In other words, lower motor neurons of the facial nerve innervate ipsilateral facial muscles.
Now, facial palsy, known as Bell's palsy, is injury of the facial nerve after it exits the pons, and it creates a palsy or paralysis of ipsilateral facial muscles. What does this mean? Well, this can occur. right basically at the facial motor nucleus, but it could occur right as the facial nerve exits the pons and goes into the internal acoustic meatus. That may occur like an acoustic neuroma, or like as the facial nerve proper descends through the facial canal, which would be something like an inflammation in there.
It could also include where mumps or a tumor in the product gland would compress the facial nerve, or just branches of the facial nerve. going into the face like what happened with Sylvester Stallone with forceps during his delivery when he was a wee baby that gives him that characteristic smile. All right, so let's do it again except with this picture. So in this picture, that is showing the facial nerve, or those axons are all part of the facial nerve, which if we then injure, you denervate both axons going to muscles of the forehead and the lower face, and that results in shing.
Complete paralysis of that side, complete paralysis of the facial muscles on that side of the lesion. So paralysis of facial muscles, half of the face is paralyzed on the side of the injury or weakness, and that results in a smooth forehead, inability to close eyes tight or to blink, a droopy nose, corner of the mouth drops, and there's a smooth face. So here's a picture of a patient, and let's do the same thing. Notice on the side of the facial palsy, a smooth forehead compared to the other side. Smooth ring around the eyes compared to the other eye and they can't close it or difficulty closing it.
Notice that this corner of the nose droops when compared to the other. And this one, if you were to say, hey show me your teeth, to a patient on the right normal side you can see the smile and teeth but on the palsy side it gives this crooked smile and then you'll notice that the faces seem smoother because the muscles are not contracting. So in facial palsy both upper and lower face are paralyzed.
Now, facial palsy is called Bell's palsy after the anatomist Sir Charles Bell, who wrote in some pamphlets and then journal articles about what he observed in this facial paralysis. He also identified this nerve called the long thoracic nerve that innervates the serratus anterior muscle. So long thoracic nerve is also called Bell's nerve.
I don't know why it didn't stick. Okay, so some orientation and some pictures. This is a lateral.
view of the brain on the right side and there is the precentral gyrus also known as the primary motor cortex and there is the pons and we're going to do a very a creative coronal cut like that and gives us a picture like this when there is our coronal section through the brain on the right side. There's the precentral gyrus and there is the pons. So now if we take a look at some other landmarks, so there's the lateral ventricle and thalamus and then there's the globus pallidus and the putamen which are part of the basal ganglia and between those structures is the internal capsule where the axons of upper motor neurons are going to course. And then there's our midbrain of the brainstem. And then there's the pons, which is going to house our facial motor nucleus.
So let's take a cross-section. And there is the facial nucleus in a cross-section of the pons. And this is what it's going to look like in our little schematic. Okay. Now, also, we see this structure called the motor homunculus.
And the motor homunculus is a somatotopic organization of the primary motor cortex. What does that mean? Well, muscles that are densely innervated think.
face are supplied by lots of neurons and therefore require more space in the cerebral cortex. And contrast, muscles that are less innervated, like the trunk, are supplied by fewer of neurons and therefore they require less space in the cerebral cortex. So let's now talk about upper motor neurons. So upper motor neurons of the facial nerve arise from the contralateral cerebral cortex. And there's an exception with the forehead, so hold that thought.
So here in this section, we see the facial nucleus. And there in the upper right cerebral cortex, by the forehead part of the homunculus, an upper motor neuron descends through the internal capsule, synapses with a lower motor neuron that goes specifically to the forehead. And then back up into the motor homunculus, you see now upper motor neuron that comes from the lower part of the face, descends and synapses with lower motor neurons.
that then innervate muscles of the lower face. So upper motor neurons of the facial nerve arise from the contralateral cerebral cortex. Bonk, bonk. But there's a forehead exception.
So what is this exception of the forehead? Well, facial motor nucleus to the forehead is stimulated by upper motor neurons from the contralateral cerebral cortex. Shing! But as well as the ipsilateral cerebral cortex as well. Shing!
That is... pretty cool. That's going to be very important in a few minutes.
Now, if we now take a look at the lower face, lower motor neurons that innervate muscles of the lower face only receive upper motor neurons from the contralateral cerebral cortex like that. So, let's do a little nutshell moment here, okay? So, lower motor neurons that innervate muscles of the upper face, okay, receive both crossed and uncrossed upper motor neurons, whereas lower motor neurons innervate muscles of the lower face receive only crossed upper motor neurons.
All right, so now what happens in a stroke is that a stroke occurs when there is an injury to a supranuclear lesion, by supranuclear meaning the facial motor nucleus, where the upper motor neuron is injured. This results in palsy of the lateral facial muscles with sparing of the forehead. What does that look like? Well, here we have a picture. And there's the facial nucleus.
And so, supernuclear lesion is anywhere in that area. Injury of the brain tissue that would injure those upper motor neurons is going to result in paralysis of the contralateral facial muscles with sparing of the forehead. So, there is a lesion. There is a lesion of upper motor neurons on the right side. And as a result, the lower motor neurons of the facial nerve on the left side do not receive innervation, which results in contralateral facial muscle paralysis like this.
But wait a Star Trek second here. You talked about that there's something funky about the forehead nucleus. So we can't forget that upper motor neurons from the ipsilateral side also can stimulate the lower motor neurons that go to that forehead. And as a result, that is what a stroke looks like. sparing of the forehead, and paralysis of contralateral lower face.
So let's do that again. That was kind of fun. So if we lesion the upper motor neurons on the right side, there is no contralateral upper motor neuron stimulation of the facial motor nucleus on the left side, but we have ipsilateral upper motor neuron innervation to the forehead like this, which then allows the forehead on the left-hand side to be stimulated.
So Sparing of the forehead on the left, paralysis of the contralateral lower face, by contralateral meaning opposite side of the lesion. All right. Now, there is an acronym FAST, F-A-S-T. FAST is an acronym to help detect and then improve responsiveness to the needs of someone who's having a stroke. So, in this acronym, F stands for facial drooping of the face.
And it's a section of the face, it's usually on one side, that's drooping and hard to move and they have this crooked smile. And then an arm, this arm weakness, like the person who may be having a stroke is unable to raise their arm fully. or they just can't even move it.
Speech, where the patient may not be either slurring their speech or not able to speak at all or understand. And then timing, if any of the symptoms above have shown facial paralysis, can't move the arm, speech problems, time is of the essence. Call emergency services, call 911, and or take them immediately to the hospital to be able to get treatment.
The faster the treatment, the better chance they have of being able to have regaining. facial movement, arm, and so forth. So here we see a patient before a stroke.
Notice that the upper forehead is wrinkling in the smile and a very beautiful symmetrical smile. Now after stroke, notice that there's sparing of the forehead on the left, but that on the left there's paralysis of that lower face, crooked smile, which means that the stroke happened on the right side. So let's do a couple of practicing, shall we?
This patient's asked to smile. Identify the most likely location of the nerve injury. There is the choices.
So pause if you want here. Now I'm going to describe, I'm going to go through and answer this question, but pause if you want to think through this on your own. So I look at this and they're like, the patient's smiling. I can see on the left they're smiling, but that on the right, there's no wrinkling of the forehead.
The right nose is drooping and the right corner of the mouth is down, which means it's all on the same side. So I'm thinking lower motor neuron lesion. And if it's on the right, that means it's a right-sided one. And the facial canal is a coursing of the motor, of lower motor neurons.
So I think it's a right facial canal problem resulting in right facial Bell's palsy. That was fun. Let's do another one.
So this patient's asked to smile, identify the most likely location of her nerve injury. Pause if you want to think through this. But I'm going to go through and describe the answer now.
So when I look at this, I'm like, all right. I can see that that corner of the right side of the mouth is drooping, as is the nose. But look, her forehead is wrinkled.
So I'm thinking now upper motor neuron problem. And it's going to be of the facial paralysis, the contralateral side. So it's a primary motor cortex in my choices. So I'm going to go with a left primary motor cortex stroke.
Okay, let's have an in a nutshell moment now. Facial or Bell's palsy is a lower motor neuron injury in the same side as the palsy and complete paralysis on that side of the face. In contrast, a stroke is an upper motor neuron injury, which is the opposite side of the palsy with lower face paralysis and sparing of the forehead. And that, my friends, is facial palsy and stroke in a nutshell.
Now, would you mind if permit me a personal moment? This is a picture of my mother, Gabriella. And about five years ago, she had her first of three strokes. And five years ago, then four years ago, she had these two strokes that gave her this characteristic feature of sparing of the forehead and paralysis of the lower face.
So her first stroke was a right-sided frontal lobe stroke. This picture shows my mom and I and our whole family, my brother Joe and my niece in the background there. And my mom, we had this wonderful night.
It was a Sunday night, the night before her 81st birthday. The whole family was there, got together. The next morning she had a massive stroke, her third that ended up six days later to when my mom died. I just wanted to say this because it's changed the way that I teach. When I talk about strokes and now other injuries and I think of the patient, I try not to be cavalier.
Not that I was before, but strokes became far more personal to me. very grateful to the family medicine docs and the neurologist that treated my mom. I gained a really big appreciation for what physical therapists do for patients with strokes and how they help my mom learn how to get up from lying down, get up from sitting and to be able to get back to walking on her own again. The occupational therapists that helped my mom relearn how to eat her food and how to brush her teeth and the speech therapists that helped my mom with. talking and trying to write. And then finally the hospice nurses that were just so heavenly sent in those last few days of my mom's life.
So just a little tribute to my mom, Gabriella Morton.