Overview of the Facial Nerve Anatomy

What's up, Time Talks Med here. Let's continue our cranial nerve series. Cranial nerves are 12 pairs of nerves that exit the brain and the brainstem. And in this segment, we will talk detailed about the 7th cranial nerve, which is the facial nerve. And we'll do that by first making a quick scheme of the facial nerve pathway. Then we will talk through the functional components and the nuclei of this nerve, since it consists of different fibers. And once we have that overview, we're going to look into the course and distribution by first going through the intracranial course and then the extracranial course and once we have gone through that we will talk a little bit about the clinical relevance. Alright so the facial nerve is responsible for providing motor innervation of the facial muscles as well as taste of the anterior 2 thirds of the tongue and production of saliva and tears. Alright so here's the scheme we will quickly run through it and then do it again in a little more detail. Within the pons and upper part of the medulla, we'll find the motor nucleus, which sends out motor fibers. We got the superior salivatory nucleus, which sends out fibers to the salivary and lacrimal glands. Then we got some sensory fibers coming in, synapsing with the spinal nucleus of the trigeminal nerve, and the nuclei of the solitary tract. These fibers will all go through the pontomedullary junction. meaning in between the pons and the medulla. And they form two fibers, they form the motor root and a smaller sensory root, or commonly referred to as the intermediate nerve. The motor root will travel through the internal acoustic meatus and enter the facial canal. In the facial canal, the facial nerve traverses forward and laterally, forming a bend, the genu of the facial nerve, where the geniculate ganglion is located. In the posterior wall of the middle ear, it gives off the nerve to the Stapetus, supplying the Stapetus muscle, and then it continues downwards towards the Stilomastoid Foramen. The superior salivatory nucleus will give off fibers that is also going to go through the geniculate ganglion, without synapsing with it, and give off the greater petrosal nerve. On its course towards the Foramen Lacerum, it merges with the deep petrosal nerve, carrying sympathetic fibers to form the nerve of the pterygoid canal. It travels to the pterygopalatine ganglion to provide preganglionic parasympathetic innervation to the lacrimal gland, as well as mucous glands of the nasal cavity, maxillary sinus, and the palate. Fibers from the superior salivatory nucleus will also branch off and give a nerve called chordotymphony. Chordotymphony exits the skull, by passing through the petrotempanic fissure to enter the infratemporal fossa. Here it terminates in the submandibular ganglion, which then sends off postganglionic fibers to innervate the submandibular and sublingual salivary glands. Chordotympani consists of two fibers, the general visceral efferent fibers, here in purple, which comes from the superior salivatory nucleus. The other components are SVA fibers, or sensory visceral afferent fibers, is the taste component of the chorda tympani. It comes from the taste receptors from the anterior 2 thirds of the tongue, and then travel with the GVE fibers, as the chorda tympani, to synapse with the sensory nuclei in the geniculate ganglion, which then sends fibers towards the nuclei of the solitary tract. A component of the facial nerve also provides sensory innervation around the external acoustic meatus and the retroauricular region. These fibers are known as general somatic afferent fibers, which travels through the stylomastoid foramen and through the facial canal to synapse with their respective nuclei in the geniculate ganglion, which then sends off fibers towards the spinal nucleus of the trigeminal nerve. Notice though that the geniculate ganglion only has cell bodies for sensory neurons, The other nerves pass through it without synapsing here. Now for the facial muscles. The motor fibers, or special visceral efferent fibers, they're going to travel further through the facial canal and leave through the stylo-mastoid foramen. It then gives off the posterior auricular nerve, which branches off as the occipital and auricular segments to innervate the occipitofrontalis muscle, and the intrinsic muscles of the ear. It will give off a stylohyoid branch and a digastric branch for the respective muscles. The facial nerve then continues into the parotid gland, branching off forming the parotid plexus, which is a plexus of nerves that give off a superior branch and an inferior branch. The superior branch gives off the temporal, zygomatic, and buccal branches, while the inferior branch gives off the parotid plexus. give off the marginal mandibular, and the cervical branch. All of these supply different muscles of the face, and we'll go through them in detail once we get here. Alright, so that was the general scheme. Awesome! Now, the facial nerve is one of the most anatomically complex of all the cranial nerves, because it transmits four different types of innervations. And so, I wanna start this video off by explaining these four functional components of this nerve, before we dive into its pathway. The first type of fibers are the Special Visceral Efferent Fibers or the SVE fibers. They begin from the motor nucleus at the level of the lower pons and supply the muscles of facial expression. Then we got the General Visceral Efferent Fibers or GVE fibers, which are preganglionic fibers, meaning they arise in the superior salivatory nucleus. Then they go to two ganglia. They go to the submandibular ganglia to further innervate the submandibular and sublingual salivary glands with the postganglionic fibers. The other ganglia it goes to is the torsopterygopaladin ganglia, which sends fibers to innervate the lacrimal gland. Then we got the special visceral afferent fibers, or SVA fibers. And notice they're afferent fibers, so they start in the periphery Or in this case, these fibers start from the taste buds in the anterior 2 thirds of the tongue. Then they synapse with neurons in the geniculate ganglion, which sends fibers further towards the brainstem, to talk with the upper part of the nucleus of the solitary tract. The last fibers are the general somatic afferent fibers, or GSA fibers. Those fibers come from the skin of the external ear primarily. And then they also synapse with cells in the geniculate ganglion, to then go further and synapse with the spinal nucleus of the trigeminal nerve. So two efferent fibers leaving the brainstem, and two afferent fibers that come into the brainstem from the geniculate ganglion. Awesome! Now let's start with the nuclei of the facial nerve. Here we see a side view of the central nervous system. We can see the spinal cord, the medulla oblongata, cerebellum, pons, mesencephalon, and the diencephalon. If we now remove the cerebellum and focus on the brainstem from the posterior side, we'll see this. So we see the mesencephalon, pons, and the medulla. On the posterior side of the brainstem, we can see something called the rhomboid fossa. And the rhomboid fossa is a key location where several cranial nerve nuclei are situated, and And because it houses so many nerves and nuclei, they form some external structures, as you can see here. In the middle, we can see the median sulcus, that divides the brainstem into two symmetrical halves. On either side, we can see the medial eminence, we can see the medullar stria, which divides pons and the medulla oblongata. And just above the medullar stria, we can find the facial colliculus. And this is what I want us to focus on here, because the facial colliculus It's a grossly elevated area on the posterior side of Pons that is formed because of the motor fibers of the facial nerve, hence the name facial colliculus. Here's a cross-section of the distal part of Pons. Here we see the abducent nerve nucleus, and the facial nucleus. When fibers from the motor nucleus of the facial nerve leaves, they loop around the abducent nerve nucleus like this, before it leaves laterally to the abducent nerve. And this loop that it makes, forms the facial colliculus. And here just for the visuals of it, we got the motor nucleus of the facial nerve, and here's the nucleus of the sixth cranial nerve, the abducent nerve. Fibers from the facial nerve will loop around the abducent nerve nucleus like this, then leave the brainstem on the anterior side between pons and the bedulla oblongata, and it will form the facial colliculus, the elevation on the backside of pons. The facial nerve is a bit special again, because it consists of 4 fibers. Most literature divide this nerve into 4 fibers, which go to 4 different nuclei. So, four nuclei are considered a part of the facial nerve. The first one is the motor nucleus, which give off SVE fibers. We got the superior salivatory nucleus, giving off GVE fibers. There's GSA fibers, coming into synapse with the spinal nucleus of the trigeminal nerve. And we got the SVA fibers, coming into synapse with the nuclei of the solitary tract. So the actual facial nerve arises from two divisions. A motor root and a smaller sensor root, commonly referred to as the intermediate nerve. So the motor root contains motor fibers. The intermediate nerve contains sensory and parasympathetic fibers of the facial nerve. Alright, now let's go through the course and distribution. And I wanna use this image to kinda illustrate just that. The facial nerve has an intracranial course and an extracranial course. The intracranial course is everything from when the nerve is within the brainstem to the point where it exits the temporal bone. An extracranial course is when it's actually outside of the cranium. I think it's easier to divide it this way. So let's start with the intracranial course. Here again, you see two nerves coming out from the junction between the pons and the medulla. We see the motor root of the facial nerve. and we see the intermediate nerve. They're both going to penetrate the dura mater and then go through the internal acoustic meatus, as you see here, to enter the facial canal in the petrous part of the temporal bone, where they fuse to form the facial nerve. The nerve makes a sharp anterior to posterior turn at a point known as the geniculum of the facial nerve. It also enlarges at this point, as the geniculate ganglion, which contains the cell bodies of sensory neurons in the facial nerve. As you look at this image, you'll notice a large nerve going out from the geniculate ganglion. This one is called the greater petrosal nerve. The greater petrosal nerve consists of parasympathetic GVE fibers, the purple ones I showed you earlier, that comes from the superior salivatory nucleus. So they don't synapse with the geniculate ganglion, They just come from the brainstem and run through the ganglion towards the foramen lacerum. On its way towards the foramen lacerum, it merges with the deep petrosal nerve that carries sympathetic fibers to form the nerve of the pterygoid canal. It travels to the pterygo palate in ganglion to provide preganglionic parasympathetic innervation to the lacrimal glands, as well as the mucous glands of the nasal cavity, maxillary sinus and palate. The second intratemporal branch of the facial nerve is the nerve to the Staphyloid muscle, supplying SVE fibers to the Staphyloid muscle, responsible for dampening vibrations and protecting the hearing apparatus when exposed to loud sounds. The final intratemporal branch is the Chorda tympani. The Chorda tympani carries gustatory or taste sensory innervation from the front of the tongue and And it carries parasympathetic innervation to the submandibular and the sublingual salivary glands. So, there are two fibers that make up the chordotymphony, GVE fibers and SVA fibers. Chordotymphony exits the skull by passing inferiorly through the petrotympanic fissure to enter the intratemporal fossa. Here chordotymphony joins with the lingual branch of the cranial nerve number 5. And together, these nerves travel anteriorly. deep to the mandible. Along the way, the GVE fibers diverge to terminate in the submandibular ganglion. From here, postganglionic neurons distribute to the submandibular and sublingual salivary glands. So GVE fibers start from the superior salivatory nucleus in the brainstem, and go straight to the submandibular ganglion. In contrast, the SVA taste component of the chord of timpani remains with the lingual nerve, where it distributes to taste receptors of the anterior two thirds of the tongue. So it carries sensory information towards the neurons in the geniculate ganglion, which further sends neurons towards the nucleus of the solitary tract. So that was primarily the intracranial course. The facial nerve exits the skull via the stylomastoid foramen, and now it's outside of the skull. So let's go through the extracranial course. after it leaves the stylo mustard for ramen. Once it exits the stylo-mastoid foramen, the facial nerve gives off the stylohyoid branch and the digastric branch. They carry motor innervation to the respective muscles. It also gives off the posterior auricular nerve, which divides into the occipital branch, to provide motor innervation to the occipital belly of the occipitofrontalis muscle, and the auricular branch, to supply mainly the intrinsic auricular muscles. And just for the sake of theory, we also got the general somatic afferent fibers, or GSA fibers, that provide sensory innervation of the skin around the external aqueous digmeatus, and the retroauricular region, which then goes to synapse with the sensory nuclei of the geniculate ganglion, from which sends fibers towards the spinal nucleus of the trigeminal nerve. Alright, so that was those. The facial nerve is then going to continue into the parotid gland. And if you fade the parotid gland, you'll see that this nerve bifurcates into a superior and an inferior trunk, which forms a network of nerves called the parotid plexus. From here, there are 5 terminal branches that are gonna come off, and they're motor. They provide motor innervation to facial muscles. The first one is the temporal branch, innervating the facial muscles of the forehead and the temporal region. We get the zygomatic branch, that innervates the orbicularis uculi, zygomatic muscles, and the muscles of the nose. There are the buccal branches, innervating the muscles of the cheek and upper lip. Marginal mandibular branch, innervating the muscles of the chin and lower lip, so the depressor labii inferiores, depressor angulo-uris, and the mentalis muscle. And then we got the cervical branch, that innervates the platysma, and in some variations, it also participates in forming the superior cervical ansa. So that was primarily all I had for the course and the distribution. Now, the facial nerve can get damaged at different levels, and with a neurological examination, you'll be able to point out the most probable site of lesions within this pathway. A damage might occur supranuclearly. The The upper motor neuron of the facial nerve is located in the primary motor cortex of the frontal lobe. These upper motor neurons will descend ipsilaterally as the cortical bulbor tract via the genu of the internal capsule, and reach the facial nucleus in the pontine tegmentum. I haven't gone into this in detail, but the facial nucleus is divided into a dorsal and ventral region. And so, the dorsal region supplies innervation of the muscles of the upper face, whereas neurons in the ventral region innervates muscles of the lower face. The dorsal aspect of the facial nucleus receives input from both the left and right cerebral hemispheres, and this results in both hemispheres having control over the muscles of the upper face. You with me so far? So if there's a stroke of some sort that affects the corticobulbar tract, you know, an upper motor neuron lesion, That will cause paralysis of the contralateral middle and lower part of the face. The muscles of the forehead and eyes are spared because they are innervated by both hemispheres. Now, lesions that involve the facial motor nucleus, or lesions to the facial nerve itself, result in complete paralysis of all the muscles on the ipsilateral side. And so, since the whole ipsilateral facial muscles are affected, The patient presents with drooping of the mouth and eyelid, as well as flattening of the nasolabial fold. Bell's palsy is a form of facial nerve palsy. It's usually idiopathic cause, meaning we're not entirely sure what causes the damage, but one theory is that it is caused by edema because of a viral infection. Bell's palsy can be distinguished from other causes of facial paralysis by rapid onset of several hours and lack of trauma. What is more is that this kind of facial paralysis is often self-limiting, and the patient usually recovers within days to weeks. And patients can benefit from early initiation of steroids as this prevents the progression of edema, diminishing chances of further damage. Alright, so that was everything I had for the facial nerve. Here we see the scheme again of this nerve. It's not detailed, but it will help to gain a general overview of this nerve. So that is this nerve. The next video is going to be about the 8th cranial nerve, the vestibulocochlear nerve. Thank you so much for watching another one of my videos. If you enjoyed, learned something from it, please remember to like, comment your favorite moment, subscribe, turn on those notifications. If you're looking for other ways to support, go ahead and check the link in the description box. Have fun y'all, peace!

And we'll do that by first making a quick scheme of the facial nerve pathway. Then we will talk through the functional components and the nuclei of this nerve, since it consists of different fibers. And once we have that overview, we're going to look into the course and distribution by first going through the intracranial course and then the extracranial course and once we have gone through that we will talk a little bit about the clinical relevance. Alright so the facial nerve is responsible for providing motor innervation of the facial muscles as well as taste of the anterior 2 thirds of the tongue and production of saliva and tears.

Alright so here's the scheme we will quickly run through it and then do it again in a little more detail. Within the pons and upper part of the medulla, we'll find the motor nucleus, which sends out motor fibers. We got the superior salivatory nucleus, which sends out fibers to the salivary and lacrimal glands. Then we got some sensory fibers coming in, synapsing with the spinal nucleus of the trigeminal nerve, and the nuclei of the solitary tract.

These fibers will all go through the pontomedullary junction. meaning in between the pons and the medulla. And they form two fibers, they form the motor root and a smaller sensory root, or commonly referred to as the intermediate nerve.

The motor root will travel through the internal acoustic meatus and enter the facial canal. In the facial canal, the facial nerve traverses forward and laterally, forming a bend, the genu of the facial nerve, where the geniculate ganglion is located. In the posterior wall of the middle ear, it gives off the nerve to the Stapetus, supplying the Stapetus muscle, and then it continues downwards towards the Stilomastoid Foramen. The superior salivatory nucleus will give off fibers that is also going to go through the geniculate ganglion, without synapsing with it, and give off the greater petrosal nerve. On its course towards the Foramen Lacerum, it merges with the deep petrosal nerve, carrying sympathetic fibers to form the nerve of the pterygoid canal.

It travels to the pterygopalatine ganglion to provide preganglionic parasympathetic innervation to the lacrimal gland, as well as mucous glands of the nasal cavity, maxillary sinus, and the palate. Fibers from the superior salivatory nucleus will also branch off and give a nerve called chordotymphony. Chordotymphony exits the skull, by passing through the petrotempanic fissure to enter the infratemporal fossa.

Here it terminates in the submandibular ganglion, which then sends off postganglionic fibers to innervate the submandibular and sublingual salivary glands. Chordotympani consists of two fibers, the general visceral efferent fibers, here in purple, which comes from the superior salivatory nucleus. The other components are SVA fibers, or sensory visceral afferent fibers, is the taste component of the chorda tympani.

It comes from the taste receptors from the anterior 2 thirds of the tongue, and then travel with the GVE fibers, as the chorda tympani, to synapse with the sensory nuclei in the geniculate ganglion, which then sends fibers towards the nuclei of the solitary tract. A component of the facial nerve also provides sensory innervation around the external acoustic meatus and the retroauricular region. These fibers are known as general somatic afferent fibers, which travels through the stylomastoid foramen and through the facial canal to synapse with their respective nuclei in the geniculate ganglion, which then sends off fibers towards the spinal nucleus of the trigeminal nerve.

Notice though that the geniculate ganglion only has cell bodies for sensory neurons, The other nerves pass through it without synapsing here. Now for the facial muscles. The motor fibers, or special visceral efferent fibers, they're going to travel further through the facial canal and leave through the stylo-mastoid foramen. It then gives off the posterior auricular nerve, which branches off as the occipital and auricular segments to innervate the occipitofrontalis muscle, and the intrinsic muscles of the ear. It will give off a stylohyoid branch and a digastric branch for the respective muscles.

The facial nerve then continues into the parotid gland, branching off forming the parotid plexus, which is a plexus of nerves that give off a superior branch and an inferior branch. The superior branch gives off the temporal, zygomatic, and buccal branches, while the inferior branch gives off the parotid plexus. give off the marginal mandibular, and the cervical branch.

All of these supply different muscles of the face, and we'll go through them in detail once we get here. Alright, so that was the general scheme. Awesome!

Now, the facial nerve is one of the most anatomically complex of all the cranial nerves, because it transmits four different types of innervations. And so, I wanna start this video off by explaining these four functional components of this nerve, before we dive into its pathway. The first type of fibers are the Special Visceral Efferent Fibers or the SVE fibers. They begin from the motor nucleus at the level of the lower pons and supply the muscles of facial expression. Then we got the General Visceral Efferent Fibers or GVE fibers, which are preganglionic fibers, meaning they arise in the superior salivatory nucleus.

Then they go to two ganglia. They go to the submandibular ganglia to further innervate the submandibular and sublingual salivary glands with the postganglionic fibers. The other ganglia it goes to is the torsopterygopaladin ganglia, which sends fibers to innervate the lacrimal gland. Then we got the special visceral afferent fibers, or SVA fibers. And notice they're afferent fibers, so they start in the periphery Or in this case, these fibers start from the taste buds in the anterior 2 thirds of the tongue.

Then they synapse with neurons in the geniculate ganglion, which sends fibers further towards the brainstem, to talk with the upper part of the nucleus of the solitary tract. The last fibers are the general somatic afferent fibers, or GSA fibers. Those fibers come from the skin of the external ear primarily.

And then they also synapse with cells in the geniculate ganglion, to then go further and synapse with the spinal nucleus of the trigeminal nerve. So two efferent fibers leaving the brainstem, and two afferent fibers that come into the brainstem from the geniculate ganglion. Awesome! Now let's start with the nuclei of the facial nerve. Here we see a side view of the central nervous system.

We can see the spinal cord, the medulla oblongata, cerebellum, pons, mesencephalon, and the diencephalon. If we now remove the cerebellum and focus on the brainstem from the posterior side, we'll see this. So we see the mesencephalon, pons, and the medulla.

On the posterior side of the brainstem, we can see something called the rhomboid fossa. And the rhomboid fossa is a key location where several cranial nerve nuclei are situated, and And because it houses so many nerves and nuclei, they form some external structures, as you can see here. In the middle, we can see the median sulcus, that divides the brainstem into two symmetrical halves. On either side, we can see the medial eminence, we can see the medullar stria, which divides pons and the medulla oblongata. And just above the medullar stria, we can find the facial colliculus.

And this is what I want us to focus on here, because the facial colliculus It's a grossly elevated area on the posterior side of Pons that is formed because of the motor fibers of the facial nerve, hence the name facial colliculus. Here's a cross-section of the distal part of Pons. Here we see the abducent nerve nucleus, and the facial nucleus. When fibers from the motor nucleus of the facial nerve leaves, they loop around the abducent nerve nucleus like this, before it leaves laterally to the abducent nerve.

And this loop that it makes, forms the facial colliculus. And here just for the visuals of it, we got the motor nucleus of the facial nerve, and here's the nucleus of the sixth cranial nerve, the abducent nerve. Fibers from the facial nerve will loop around the abducent nerve nucleus like this, then leave the brainstem on the anterior side between pons and the bedulla oblongata, and it will form the facial colliculus, the elevation on the backside of pons. The facial nerve is a bit special again, because it consists of 4 fibers.

Most literature divide this nerve into 4 fibers, which go to 4 different nuclei. So, four nuclei are considered a part of the facial nerve. The first one is the motor nucleus, which give off SVE fibers. We got the superior salivatory nucleus, giving off GVE fibers. There's GSA fibers, coming into synapse with the spinal nucleus of the trigeminal nerve.

And we got the SVA fibers, coming into synapse with the nuclei of the solitary tract. So the actual facial nerve arises from two divisions. A motor root and a smaller sensor root, commonly referred to as the intermediate nerve. So the motor root contains motor fibers. The intermediate nerve contains sensory and parasympathetic fibers of the facial nerve.

Alright, now let's go through the course and distribution. And I wanna use this image to kinda illustrate just that. The facial nerve has an intracranial course and an extracranial course. The intracranial course is everything from when the nerve is within the brainstem to the point where it exits the temporal bone. An extracranial course is when it's actually outside of the cranium.

I think it's easier to divide it this way. So let's start with the intracranial course. Here again, you see two nerves coming out from the junction between the pons and the medulla.

We see the motor root of the facial nerve. and we see the intermediate nerve. They're both going to penetrate the dura mater and then go through the internal acoustic meatus, as you see here, to enter the facial canal in the petrous part of the temporal bone, where they fuse to form the facial nerve.

The nerve makes a sharp anterior to posterior turn at a point known as the geniculum of the facial nerve. It also enlarges at this point, as the geniculate ganglion, which contains the cell bodies of sensory neurons in the facial nerve. As you look at this image, you'll notice a large nerve going out from the geniculate ganglion. This one is called the greater petrosal nerve.

The greater petrosal nerve consists of parasympathetic GVE fibers, the purple ones I showed you earlier, that comes from the superior salivatory nucleus. So they don't synapse with the geniculate ganglion, They just come from the brainstem and run through the ganglion towards the foramen lacerum. On its way towards the foramen lacerum, it merges with the deep petrosal nerve that carries sympathetic fibers to form the nerve of the pterygoid canal. It travels to the pterygo palate in ganglion to provide preganglionic parasympathetic innervation to the lacrimal glands, as well as the mucous glands of the nasal cavity, maxillary sinus and palate. The second intratemporal branch of the facial nerve is the nerve to the Staphyloid muscle, supplying SVE fibers to the Staphyloid muscle, responsible for dampening vibrations and protecting the hearing apparatus when exposed to loud sounds.

The final intratemporal branch is the Chorda tympani. The Chorda tympani carries gustatory or taste sensory innervation from the front of the tongue and And it carries parasympathetic innervation to the submandibular and the sublingual salivary glands. So, there are two fibers that make up the chordotymphony, GVE fibers and SVA fibers. Chordotymphony exits the skull by passing inferiorly through the petrotympanic fissure to enter the intratemporal fossa.

Here chordotymphony joins with the lingual branch of the cranial nerve number 5. And together, these nerves travel anteriorly. deep to the mandible. Along the way, the GVE fibers diverge to terminate in the submandibular ganglion. From here, postganglionic neurons distribute to the submandibular and sublingual salivary glands. So GVE fibers start from the superior salivatory nucleus in the brainstem, and go straight to the submandibular ganglion.

In contrast, the SVA taste component of the chord of timpani remains with the lingual nerve, where it distributes to taste receptors of the anterior two thirds of the tongue. So it carries sensory information towards the neurons in the geniculate ganglion, which further sends neurons towards the nucleus of the solitary tract. So that was primarily the intracranial course.

The facial nerve exits the skull via the stylomastoid foramen, and now it's outside of the skull. So let's go through the extracranial course. after it leaves the stylo mustard for ramen. Once it exits the stylo-mastoid foramen, the facial nerve gives off the stylohyoid branch and the digastric branch.

They carry motor innervation to the respective muscles. It also gives off the posterior auricular nerve, which divides into the occipital branch, to provide motor innervation to the occipital belly of the occipitofrontalis muscle, and the auricular branch, to supply mainly the intrinsic auricular muscles. And just for the sake of theory, we also got the general somatic afferent fibers, or GSA fibers, that provide sensory innervation of the skin around the external aqueous digmeatus, and the retroauricular region, which then goes to synapse with the sensory nuclei of the geniculate ganglion, from which sends fibers towards the spinal nucleus of the trigeminal nerve.

Alright, so that was those. The facial nerve is then going to continue into the parotid gland. And if you fade the parotid gland, you'll see that this nerve bifurcates into a superior and an inferior trunk, which forms a network of nerves called the parotid plexus.

From here, there are 5 terminal branches that are gonna come off, and they're motor. They provide motor innervation to facial muscles. The first one is the temporal branch, innervating the facial muscles of the forehead and the temporal region.

We get the zygomatic branch, that innervates the orbicularis uculi, zygomatic muscles, and the muscles of the nose. There are the buccal branches, innervating the muscles of the cheek and upper lip. Marginal mandibular branch, innervating the muscles of the chin and lower lip, so the depressor labii inferiores, depressor angulo-uris, and the mentalis muscle. And then we got the cervical branch, that innervates the platysma, and in some variations, it also participates in forming the superior cervical ansa.

So that was primarily all I had for the course and the distribution. Now, the facial nerve can get damaged at different levels, and with a neurological examination, you'll be able to point out the most probable site of lesions within this pathway. A damage might occur supranuclearly. The The upper motor neuron of the facial nerve is located in the primary motor cortex of the frontal lobe. These upper motor neurons will descend ipsilaterally as the cortical bulbor tract via the genu of the internal capsule, and reach the facial nucleus in the pontine tegmentum.

I haven't gone into this in detail, but the facial nucleus is divided into a dorsal and ventral region. And so, the dorsal region supplies innervation of the muscles of the upper face, whereas neurons in the ventral region innervates muscles of the lower face. The dorsal aspect of the facial nucleus receives input from both the left and right cerebral hemispheres, and this results in both hemispheres having control over the muscles of the upper face.

You with me so far? So if there's a stroke of some sort that affects the corticobulbar tract, you know, an upper motor neuron lesion, That will cause paralysis of the contralateral middle and lower part of the face. The muscles of the forehead and eyes are spared because they are innervated by both hemispheres.

Now, lesions that involve the facial motor nucleus, or lesions to the facial nerve itself, result in complete paralysis of all the muscles on the ipsilateral side. And so, since the whole ipsilateral facial muscles are affected, The patient presents with drooping of the mouth and eyelid, as well as flattening of the nasolabial fold. Bell's palsy is a form of facial nerve palsy. It's usually idiopathic cause, meaning we're not entirely sure what causes the damage, but one theory is that it is caused by edema because of a viral infection.

Bell's palsy can be distinguished from other causes of facial paralysis by rapid onset of several hours and lack of trauma. What is more is that this kind of facial paralysis is often self-limiting, and the patient usually recovers within days to weeks. And patients can benefit from early initiation of steroids as this prevents the progression of edema, diminishing chances of further damage. Alright, so that was everything I had for the facial nerve. Here we see the scheme again of this nerve.

It's not detailed, but it will help to gain a general overview of this nerve. So that is this nerve. The next video is going to be about the 8th cranial nerve, the vestibulocochlear nerve.

Thank you so much for watching another one of my videos. If you enjoyed, learned something from it, please remember to like, comment your favorite moment, subscribe, turn on those notifications. If you're looking for other ways to support, go ahead and check the link in the description box.

Have fun y'all, peace!

Transcript for:Overview of the Facial Nerve Anatomy

Transcript for:
Overview of the Facial Nerve Anatomy