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The hypoglossal nerve is a purely motor nerve responsible for controlling the movement of the tongue. It plays a crucial role in tongue mobility and articulation, making it essential for speech and swallowing.
Motor fibers of the ventral branches of the first and second cervical spinal nerves join the hypoglossal nerve. Some of these fibers leave the hypoglossal nerve via the superior root to join the inferior root, forming the ansa cervicalis (plexus cervicalis). Other fibers travel via the hypoglossal nerve to supply the geniohyoid muscle and give off a meningeal branch for the dura mater in the inferior part of the posterior cranial fossa.
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Introduction
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What’s up, Taim Talks Med here. Let’s continue our Cranial nerve series. Cranial nerves are
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twelve pairs of nerves that exit the brain and the brainstem, and in this segment,
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we’ll talk detailed about the twelfth cranial nerve, the hypoglossal nerve.
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And we’ll do that by first drawing a quick scheme of the hypoglossal nerve pathway.
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We will talk about the distribution of nuclei and the course of this nerve. And then go through the
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branches and its associated nerves. Awesome. Now the hypoglossal nerve
Hypoglossal Nerve Scheme
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is relatively easy. It is purely a motor nerve, responsible for controlling the movement of the
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tongue. Which means that it plays a crucial role in tongue mobility and articulation,
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making it essential for speech and swallowing. The hypoglossal nerve originates from the nucleus
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of the hypoglossal nerve, located within medulla oblongata. The nerve is going to give off somatic
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efferent fibers, or motor fibers, that’re going to go out from the brainstem in the sulcus between
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the olive and pyramid. We call it the pre-olivary groove. It then travels a short distance within
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the cranial cavity, and then exits the skull through the hypoglossal canal. As the nerve
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is now outside the cranium, it travels between the internal carotid artery and the internal
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jugular vein, to then form an arch we call arch of the hypoglossal nerve. It then goes towards
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the tongue and give off lingual branches to supply the muscles of the tongue, which
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primarily include the extrinsic muscles, you know the genioglossus, Styloglossus and hyoglossus. And
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the intrinsic muscles, which are the superior and inferior longitudinal lingual muscles, and
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the vertical and transverse muscles of the tongue. The hypoglossal nerve is closely related with the
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cervical plexus, in that the anterior ramus of the 1st and 2nd cervical spinal nerves are going to
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send some motor fibres towards the hypoglossal nerve, that travels with the hypoglossal nerve
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to supply the geniohyoid muscle. When you study the hypoglossal nerve, you might find
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some variations that mention a meningeal branch, coming from the sensory spinal ganglion of C2,
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that also might run through the hypoglossal canal and help innervates the dura mater in
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the floor of the posterior cranial fossa. The hypoglossal nerve will also send some
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motor fibres along the superior root of the ansa cervicalis, that go together with the inferior
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root of ansa cervicalis, from the C2 and C3, to form a nice loop called ansa cervicalis. So
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that is the general scheme of this nerve and it’s associated branches. Now what I
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wanna do is go through this scheme in a little more detail, and we’ll start with the nucleus.
Nucleus of Hypoglossal Nerve
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So here you see the spinal cord, the medulla oblongata, Cerebellum, Pons, Mesencephalon and
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the diencephalon. If we now go ahead and focus only on the lateral aspect of the brainstem,
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we can see that the nucleus of the hypoglossal nerve is located within the medulla oblongata.
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The nucleus of the hypoglossal nerve is going to give off a series of rootlets that’re going
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to go our from the brainstem in the pre-olivary sulcus, so between the pyramid and the olive. If
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we now change it up with a little more realistic view, you’ll see the that the rootlets leave the
Course of Hypoglossal Nerve
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brainstem between the olive and the pyramid. Now what happens is, this nerve is going to
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travel within the hypoglossal canal, as you see here, and through the hypoglossal canal,
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it’s going to leave the cranium. When it leaves the cranium, it’ll pass between the internal
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carotid artery, and the internal jugular vein as you see here. Then It’s going to form an arch as
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it passes forward towards the tongue. When it reaches the tongue, it’ll give
Branches of Hypoglossal Nerve
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off the lingual branches that’s going to supply several muscles in the tongue. The
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muscles that it’s going to supply is the styloglossus, which causes retraction of
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the tongue and elevation of the body and apex of the tongue. It’ll innervate the hyoglossus,
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which causes depression and retraction of the tongue. It’s going to supply the genioglossus,
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which causes protrusion and depression of the tongue. Another small muscle it’s going to
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innervate is the chondroglossus muscle, which is a tiny muscle that helps with the depression of
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the tongue. Alright so the hypoglossal nerve will innervate the extrinsic muscles of the
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tongue, which are all involved in movement of the tongue. Now if we cut the tongue in the middle,
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and then look at the tongue from this perspective, we’ll be able to see the muscles within the tongue
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itself. And those are the superior longitudinal lingual, and the inferior longitudinal lingual
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muscle, involved in shortens the length of the tongue. There’s the vertical lingual,
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involved in flattening and broadening the tongue. And there’s the transverse lingual muscles, which
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narrows the tongue. These muscles are categorized as the intrinsic muscles of the tongue,
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and they’re involved in changing the actual shape of the tongue. All of these muscles are
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going to be innervated by the hypoglossal nerve. Now, there is another relation that we need to
Cervical Plexus
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talk about when it comes to the hypoglossal nerve. And that is that this nerve is closely
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related with the cervical plexus, highlighted here. So what happens is that the anterior ramus
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of C1 and C2 will join the hypoglossal nerve, and travel with it to innervate the geniohyoid muscle.
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A meningeal branch that come from the sensory spinal ganglion of spinal nerve C2, might also
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travel alongside the hypoglossal nerve, go through the hypoglossal canal to help innervate the dura
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mater of the floor of the posterior cranial fossa. Now when you look at this image, you’ll also see
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that fibers from the hypoglossal nerve go towards the superior root of ansa cervicalis, which joins
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the inferior root of of ansa cervicalis from C2 and C3, to form this nice loop here. The ansa
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cervicalis that is a part of the cervical plexus. Alright. So that was everything I had for this
Recap
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nerve. Here again you see the scheme for the hypoglossal nerve. It’s just schematic,
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not exactly anatomically correct but I hope it’ll help you gain a good understanding of this nerve.
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So, we now covered the hypoglossal nerve, which is the last of all the cranial nerves in our
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cranial nerve playlist. In the next video, I will quickly go through the schemes of each
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cranial nerve. Kind of unite all of them in one video so you have them all in one place
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in case you need to memorize them all. Thank you so much for watching another
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one of my videos. If you enjoyed, learned something from it, please remember to like,
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