Description

Glossopharyngeal Nerve Overview

The glossopharyngeal nerve plays a crucial role in transmitting sensory information from the back of the throat, taste sensations, and saliva production. It is also involved in swallowing and speaking.

Functional Components of the Glossopharyngeal Nerve

• Special visceral efferent fibers (SVE) (branchial motor): Supply motor innervation to the stylopharyngeus muscle, which elevates the larynx and pharynx during speaking and swallowing.
• General visceral efferent fibers (GVE) (visceral motor): Provide parasympathetic innervation to the parotid glands. Fibers originate in the inferior salivatory nucleus, travel with the tympanic nerve through the foramen ovale, and synapse at the otic ganglion.
• General visceral afferent fibers (GVA) (visceral sensory): Carry sensory information from the carotid sinus and carotid body.
• Special visceral afferent fibers (SVA): Provide taste afferents from the posterior third of the tongue.
• General somatic afferent fibers (GSA) (general sensory): Provide sensory innervation to the upper pharynx, inner surface of the tympanic membrane, and the posterior third of the tongue.

Nuclei of the Glossopharyngeal Nerve

• Nucleus ambiguus: Motor nucleus
• Inferior salivatory nucleus (nucleus salivatorius inferior): Parasympathetic visceromotor nucleus
• Nuclei of the solitary tract (nuclei tractus solitarii): Viscerosensory nucleus
• Gustatory nucleus (nucleus gustatorius): Special sensory nucleus
• Spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini): Somatosensory nucleus

Course of the Glossopharyngeal Nerve

Intracranial Course

The glossopharyngeal nerve emerges from the medulla as a series of rootlets between the olive and the inferior cerebellar peduncle. It traverses the posterior cranial fossa and exits through the jugular foramen (foramen jugulare).

Extracranial Course

The superior and inferior ganglia of the glossopharyngeal nerve are situated at the exit, after which it gives off its side branches.

Branches of the Glossopharyngeal Nerve

• Tympanic nerve (nervus tympanicus)
  • Lesser petrosal nerve (nervus petrosus minor)
• Carotid branch (ramus sinus carotici)
• Lingual branches (rami linguales)
• Stylopharyngeal branch (ramus stylopharyngeus)
• Pharyngeal branches (rami pharyngei)
• Tonsillar branches (rami tonsillares)

Sources

• Singh, I. (2017). Human Neuroanatomy (10th ed.).
• Kozlowski, T. (2017). Memorix Anatomy: The Complete Study Guide. 2nd ed. Thieme Medical Publishers.
• Neuroanatomy, Cranial Nerve 9 (Glossopharyngeal). Kathryn Thomas; Katrina Minutello; Joe M Das.

Pictures and Visuals

• Complete Anatomy
• Biorender
• PowerPoint
• Camtasia 2021

Transcript

Introduction
0:06
What’s up, Taim Talks Med here.
0:08
Let’s continue our Cranial nerve series.
0:11
Cranial nerves are twelve pairs of nerves that exit the brain and the brainstem, and
0:15
in this segment, we’ll talk detailed about the nineth cranial nerve, the glossopharyngeal
0:20
nerve.
0:21
And we’ll do that by first making a quick scheme of the glossopharyngeal nerve pathway.
0:26
Then we’ll break down the functional components of this nerve along with it’s respective
0:31
nuclei in the medulla.
0:32
We’ll go through the course and distribution by going through its intracranial course first,
0:38
then the extracranial course and its branches.
0:42
just a quick note before we start.
0:44
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0:49
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0:51
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0:56
Alright let’s continue to the video.
Glossopharyngeal Nerve Scheme
0:58
Alright, let’s start making a little scheme and then we’ll talk about it in detail.
1:03
Now, the glossopharyngeal nerve plays a crucial role in transmitting sensory information from
1:09
the back of the throat, taste sensations and saliva production, and is involved in swallowing
1:15
and speaking.
1:17
This nerve has altogether 4 nuclei that are located whithin the medulla oblongata.
1:22
We got a nucleus ambiguous which is a motor nucleus.
1:27
Inferior salivatory nucleus which is parasympathetic, nucleu of solitary tract which is functionally
1:33
divided into a viscerosensory part and a gustatory part for taste.
1:39
And we got the spinal nucleus of the trigeminal nerve which is somatosensory.
1:45
Now what happens it, nerves are going to go in and out through the medulla, on the lateral
1:51
aspect of the olive, called the retroolivary groove.
1:54
So It has a motor component, parasympathetic component, and the sensory components.
2:01
The motor part will go through the jugular foramen, through the superior and the inferior
2:07
ganglion of the glossopharyngeal nerve, then it’s going to go and innervate the stylopharyngeus
2:13
muscle.
2:14
Then we got a parasympathetic component that takes a little bit of a complicated route.
2:19
It’s going to go through the jugular foramen, then give off the tympanic nerve.
2:25
The tympanic nerve is going to go through the tympanic cancliculus and then enter the
2:30
tympanic cavity.
2:32
Within the tympanic cavity, it’s going to form the neural tympanic plexus.
2:37
This plexus is formed by two other nerves aswell, one being the sympathetic caroticotympanic
2:42
nerves that extend from the internal carotid plexus, and a small branch from the facial
2:48
nerve called the communicant branch of the tympanic plexus.
2:52
But from the tympanic plexus, there is a parasympathetic branch that’s going to out called the lesser
2:59
petrosal nerve.
3:00
It goes through the canal of the lesser petrosal nerve and leaves the cranium as it passes
3:05
though the sphenopetrosal fissure, or foramen ovale, or petrosal foramen, there are variations
3:11
to this nerve on how it exits the skull, but primarily I think most sources say the foramen
3:16
ovale.
3:18
But what you need to know is that this nerve will provide preganglionic parasympathetic
3:23
innervation to the otic ganglion, which then form postganglionic parasympathetic fibers
3:29
that run together with the auriculotemporal nerve of the trigeminal nerve, to innervate
3:34
the parotid gland and make it salivate.
3:37
Alright, let’s continue to the sensory ones.
3:41
There are fibers that come from the carotid body and sinus, from the baroreceptors and
3:45
chemoreceptors there.
3:47
They’re going to go take these impulses towards the inferior ganglion of the glossopharyngeal
3:52
nerve, and then go synapse with the nucleus of the solitary tract.
3:56
Then there are some special sensory fibers for the sense of taste from the posterior
4:01
one-third of the tongue.
4:03
These fibers are going to take fibers towards the inferior ganglion, then go further and
4:09
synapse with the gustation part of the solitary tract.
4:14
The last fibers which I’ve highlighted in green here are somatic sensory fibers innervating
4:20
mucosal membranes along different regions.
4:23
There are general sensory fibers coming from the posterior 1/3 of the tongue, and taking
4:29
these impulses towards cell bodies in the superior ganglion of the glossopharyngeal
4:33
nerve.
4:35
Then fibers are gonna continue off towards the spinal nucleus of the trigeminal nerve.
4:40
So we got two fibers now from the posterior 1/3 of the tongue.
4:44
One part for taste and one part for general sensory like touch, pain and temperature.
4:50
Then there’s a branch coming in along the tympanic nerve from the mucus membranes of
4:54
the middle ear, tympanic membrane and part of the external ear.
4:59
Then there’s a large area in the pharyngeal region that is supplied by this nerve, though
5:04
the pharyngeal plexus.
5:06
This plexus is formed from the union of branches from the vagus nerve, laryngopharyngeal nerves
5:12
from the cervical sympathetic plexus, and the glossopharyngeal nerve.
5:17
So fibers for the glossopharyngeal nerve will also take fibers towards the superior ganglion
5:24
and then to the spinal nucleus of the trigeminal nerve.
5:27
There’re also fibers froming from mucus membranes of the palatine tonsils.
5:33
So this is the general scheme of this nerve.
Functional Components
5:35
It’s not really that complicated, but one thing I want you to understand before we talk
5:40
about this in a little more detail, and you probably already see it from the color coding
5:44
here, but we generally divide this nerve into functionally different components and it’s
5:50
so easy to remember it like this.
5:53
So the glossopharyngeal nerve is a mixed nerve, it has a motor component, sensory component
6:00
and a parasympathetic component.
6:02
The motor component innervates the stylopharyngeus muscle and the parasympathetic fibres towards
6:08
the parotid gland for saliva production.
6:11
The sensory is subdivided into visceral part and somatic part.
6:16
And visceral is further subdivided into two parts.
6:20
General visceral sensory fibres from carotid bodies, and special visceral for the sense
6:25
of taste of the posterior 1/3 of the tongue.
6:29
The somatic sensory fibres coming in from all the different regions within the pharyngeal
6:34
and the middle ear area.
6:36
So, this is how it looks like.
6:39
Special visceral efferent fibers are motor fibers that go to the stylopharyngeus muscle
6:45
with its central nuclei being nucleus ambiguous.
6:49
General visceral efferent fibers being parasympathetic fibers coming from the inferior salivatory
6:55
nucleus, going out as the tympanic nerve, forming the tympanic plexus, then through
7:01
the lesser petrosal nerve providing preganglionic parasympathetic fibers to the otic ganglion,
7:07
which sends fibers further to the partoid gland.
7:11
There are general visceral afferent fibers from the carotid sinus and body, taking information
7:17
towards the inferior ganglion of the glossopharyngeal nerve, then to the nucleus of the solitary
7:23
tract.
7:24
There are special visceral afferent fibers fort he sense of taste in the posterior 1/3
7:30
of the tongue, going towards the inferior ganglion, then towards the nucleus of the
7:35
solitary tract, and there are general somatic afferent fibers, that take in general sensory
7:42
information from the pharynx, tympanic memebranes and the posterior 1/3 of the tongue, towards
7:47
the superior ganglion of the glossopharyngeal nerve, then towards the spinal nucleus of
7:52
the trigeminal nerve.
7:54
Alright.
7:55
Knowling all that, let us dive into the actual pathway in a visual setting starting with
Nuclei of Glossopharyngeal Nerve
8:00
the nuclei.
8:01
So, here you see the spinal cord, medulla oblongata, cerebellum, Pons, Mesencephalon
8:07
and the diencephalon.
8:09
If we now focus on the lateral aspect of the brainstem, you’ll see this.
8:14
So again we got the nucleus ambiguous, giving off the special visceral efferent fibres,
8:19
so motor fibres.
8:21
There are the nuclei of the solitary tract receiving both general visceral afferent fibres
8:27
from the carotid sinus and the carotid body, as well as special visceral afferent fibres
8:33
from the taste sensation of the tongue.
8:36
There are the Inferior salivatory nucleus giving off general visceral efferent fibres,
8:42
so parasympathetic innervation of the parotid gland, and there’s the spinal nucleus fo
8:48
the trigeminal nerve, getting general somatic afferent fibres.
8:52
They’re all going to go out from the medulla oblongata from the posterolateral part of
8:57
the medullary olive.
Intracranial Course
8:59
From here, we can divide its course into intracranial course, and extracranial course, and the dividing
9:06
line between them would be the jugular foramen, from where this nerve exits the cranium.
9:12
There’s really not much to talk about when it comes to the intracranial course luckily,
9:16
since it doesn’t branch off at this point.
9:19
All it does it emerge from the medulla as series of rootlets between the olive and the
9:23
inferior cerebellar peduncle.
9:26
It then goes along the cranial fossa and exits through the jugular foramen.
9:31
Let us now look at this image from this perspective, we’ll see this.
Extracranial Course
9:36
After it exits the jugular foramen, you’ll immediately see two ganglia, if we zoom in,
9:41
you’ll see them better.
9:43
These are called the superior ganglion of the glossopharyngeal nerve, and the inferior
9:48
ganglion of the glossopharyngeal nerve, or you can also call it the petrous ganglion.
9:53
And the reason why I’m being so specific here is because the vagus nerve also has a
9:58
superior ganglion and an inferior ganglion, so I wanna be very very specific in saying
10:03
the superior and inferior ganglion of the glossopharyngeal nerve.
10:08
Alright, let’s go through some side branches and the first one that I wanna talk about
Tympanic Nerve
10:13
here is called the tympanic nerve.
10:16
And again this nerve contain the parasympathetic branch of the glossopharyngeal nerve, as well
10:21
as some general somatic afferent fibers.
10:24
It’s going to ascend upwards though the tympanic canaliculus and enter the tympanic
10:30
cavity.
10:31
When it reaches the tympanic cavity, the tympanic nerve forms the tympanic plexus along with
10:36
two other nerves.
10:38
The two other nerves that help forming this plexus are the sympathetic caroticotympanic
10:43
nerves from the internal caotid plexus and a branch from the facial nerve called the
10:49
communicant branch.
10:51
The tympanic plexus then sends branches that will innervate the the area of the middle
10:55
ear, tympanic membrane and some parts of the external ear, and send these general somatic
11:01
afferent fibers towards the superior ganglion of the glossopharyngeal nerve, then towards
11:06
the spinal nucleus of the trigeminal nerve.
11:10
From the superior part of the plexus, the lesser petrosal nerve is going to come out.
11:16
It then extends upwards, passing through the canal of the lesser petrosal nerve, to reaches
11:21
the anterior side of the temporal pyramid.
11:25
The nerve leaves the cranium as it passes through the foramen ovale, or some variations
11:30
might say sphenopetrosal fissure or the petrosal foramen.
11:34
It finally ends in the otic ganglion.
11:37
This is important because the lesser petrosal nerve carries the secretory parasympathetic
11:42
fibers that synapse with the cells of the otic ganglion.
11:46
In that way, the postganglionic fibers join the auriculotemporal nerve from the trigeminal
11:52
nerve to reach the parotid gland and supply it with the parasympathetic innervation that
11:58
is necessary for the proper salivation.
Carotid Sinus Nerve
12:01
So that is this nerve.
12:03
Next we got the carotid sinus nerve.
12:06
This nerve consists of the general visceral afferent fibers that descends along the body
12:11
of the internal carotid artery aiming towards the bifurcation of the common carotid artery.
12:17
It ends by sending terminal branches to the carotid sinus and the carotid body.
12:22
So what it does is that it transmits sensory information from chemoreceptors in the carotid
12:27
bodies, helping to regulate blood oxygen and carbon dioxide levels, and sensory information
12:34
from the baroreceptors located in the carotid sinus, aiding in the regulation of blood pressure.
12:40
Those fibers will take signals towards the inferior ganglion of the glossopharyngeal
12:45
nerve, then send the fibers further towards the nuclei of the solitary tract.
Lingual Branches
12:52
Then we got the lingual branches, which are terminal branches of the glossopharyngeal
12:56
nerve.
12:57
It’s going to go towards the posterior one-third of the tongue, and provide two types of fibers.
13:03
What were those two fibers?
13:06
The lingual branches contain special visceral afferent fibers that provides the sense of
13:11
taste from the vallate papillae, taking the sensations towards the inferior ganglion,
13:17
then towards the nucleus of the solitary tract.
13:20
It also contain some general somatic afferent fibers, providing general sensory information
13:26
from the posterior 1/3 of the tongue aswell, taking these impulses towards the superior
13:32
ganglion and then towards the spinal nucleus of the trigeminal nerve.
13:37
So that is that one.
Stylopharyngeal Branch
13:39
Next we got the stylopharyngeal nerve.
13:42
This is a motor branch, or special visceral efferent fibers providing motor innervation
13:48
for the stylopharyngeus muscle.
13:50
It goes down and reaches the muscle from its lateral surface as you see here.
13:55
This muscle specifically helps which basically elevating the pharynx during swallowing and
14:01
speech, it’s a small but a very important muscle swallowing and speech.
Pharyngeal Branches
14:07
Alright.
14:08
Then we got the pharyngeal branches, which remember are general somatic afferent fibers,
14:14
that take in general somatic information from several regions in the pharynx towards the
14:19
superior ganglion of the glossopharyngeal nerve, then further towards the spinal nucleus
14:24
of the trigeminal nerve.
14:27
What happens is, three nerves go towards the pharynx and go together forming a plexus called
14:33
the pharyngeal plexus.
14:35
Those nerves are branches from the vagus nerve, laryngopharyngeal nerves from the cervical
14:40
sympathetic plexus, as well as the pharyngeal branches from the glossopharyngeal nerve.
14:46
The sensory component belongs to the glossopharyngeal nerve, but this plexus do provide motor innervation
14:53
to pharyngeal muscles aswell through the vagus nerve.
Recap
14:56
Alright.
14:57
So that was everything I had for the glossopharyngeal nerve.
15:00
Here again you see the scheme for the glossopharyngeal nerve.
15:03
It’s just schematic, not exactly anatomically correct but I hope it’ll help you gain a
15:08
good understanding of this nerve.
15:10
So, we now covered the glossopharyngeal nerve.
15:14
The next video is going to be about the tenth cranial nerve, the vagus nerve.
15:18
Thank you so much for watching another one of my videos.
15:21
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15:25
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15:26
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15:27
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15:32
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15:38
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