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Introduction
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What’s up! Taim Talks Med here. Let’s talk about the Cervical Plexus!
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The cervical plexus is extremely important because it’s gonna supply
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many structures in the head in the neck, and even some other muscles that we’ll talk about.
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Now we’re gonna talk about in a series of videos, we’re gonna talk about the cervical, the brachial
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plexus, the lumbar, the sacral. And then we’re gonna talk about the intercostal nerves.
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So the way I wanna explain this plexus to you all is go through from the very basic,
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to innervation and then some clinical relevance. So first we’re gonna go through the topography.
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Just talk a little bit about where these nerves come from specifically.
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Then we’re gonna make a scheme of the cervical plexus.
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And to make this scheme, we’ll first go through the somatosensory branches of the cervical plexus.
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We’re gonna go through the motor branches and talk a little bit about the mixed branch
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that the cervical plexus contributes to. Now don’t get mad at me for simplifying
Topography of Cervical Plexus
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it too much now. But here you see the very basic vertebral bodies and the spinous processes of the
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vertebrae, forming the vertebral canal. And within the vertebral canal, you’ll find the spinal cord.
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And here we see the spinal cord divided into the cervical segments in orange, then the thoracic
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segments, the lumbar segments, sacral segments. And then a tiny end the conus medullaris,
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from where the coccygeal nerve goes out from. Each spinal cord segment give off two spinal
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nerves. One on each side. And they leave the vertebral cala through the intervertebral
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foramen. Here they’re super simplified, I know it looks like they’re leaving from between the
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vertebral bodies, but they’re not. They leave through the intervertebral foramen on each side.
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Once the spinal nerve leaves the vertebral canal, it starts dividing into a posterior branch,
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which innervates the back. It divides into an anterior branch, which innervates
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the anterior part of the trunk and limbs. There’s a meningeal branch that goes back into the
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vertebral canal to innervate the spinal meninges. And then there’re the rami communicans,
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connected to the sympathetic chain ganglia. Or the paravertebral ganglia.
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But what’s important now for this video, is the anterior branch of the spinal nerve.
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Because the anterior branch is what forms all the plexuses that we’re
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going to talk about in this series of videos. So, cervical plexus, formed by the spinal nerves.
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Which branch of the spinal nerves? The anterior branch.
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More specifically. The cervical plexus is formed by spinal nerve number 1, 2, 3, and 4.
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Let’s now go ahead and simplify this drawing so that we can actually make a scheme out of this.
Somatosensory Nerves of Cervical Plexus
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Now what I want you to do, is to gram a piece of paper and a pen, and I want you
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to draw this scheme with me. Once you do that, I promise you’ll remember this much much easier.
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Alrgiht. Now the first thing we can do, is to connect
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C2 and C3 together, And C3 and C4 together. Then we can make an extra connection
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between C2 and C3 here aswell. The first branch that we’re gonna talk about now,
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is a branch that’s actually going to traverse this way. This Is called the Transverse Cervical Nerve.
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And the transverse cervical nerve is actually gonna be important because it
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innervates the skin on the anterior aspect of the neck, and the lateral aspect of the neck.
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If you wanna be very detaily about this one. You can also see that it actually divides into an
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inferior branch which innervated the skin of the infrahyoid region. And a superior branch, which
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innervated the skin of the suprahyoid region. And from the superior branch, this is vert detailed,
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but the superior branch can have nerves that form a looping connection with the facial nerve
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superficially, called the superficial ansa cervicalis, supplying the platysma.
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Then posteriorly, we got the greater auricular nerve and the lesser occipital nerve.
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And the greater auricular nerve which is actually consisting of the C2 and the C3 branches,
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it’s gonna supply the skin over the ear. And the skin lying over the parotid gland.
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So it’s also a somatosensory nerve. Again if you wanna be too detaily here aswell.
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You do have an anterior branch for the anterior part of the auricle and the parotic region,
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and a posterior brancg for the posterior aspect fof the auricle and the parotid region.
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The lesser occipital. Some literature say it comes from the C2 and the C3,
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and other say it only comes from the C2. So we’re just gonna have that here but keep in mind that
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this can be changed depending on the literature you’re studying from. But the lesser occipital
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nerve is gonna supply the skin of the occiput, as well as the posterior aspect of the neck and the
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actual lateral aspect of the back of the neck. Now. C3 and C4 will go together, and form
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what’s called the supraclavicular nerves. The supraclavicular nerve will go down and divide
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into the medial supraclavicular nerve, innervating the skin over the manubrium of the sternum.
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It’ll give off an intermediate supraclavicular nerve, innervating the skin of the infraclavicular
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region. And a lateral supraclavicular nerve, innervating the skin of the acromial region.
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These four nerves you see here, are what’s called the Somatosensory nerves of the cervical plexus.
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Meaning they’re superficially located, and they transfer information from mechanoreceptors,
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exteroceptors, proprioceptors, and thermoreceptors on the body surface. So, in other words, these
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fibers take in information like touch, pressure, vibration, temperature, itch, tickle, and pain.
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So that was the somatosensory nerves. Let’s do the motor nerves.
Motor Nerves of Cervical Plexus
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Now. C1 and C2 are going to give off branches towards one another.
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They’re gonna communicate with one another. From this connection, as well as from C2, C3 and C4,
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there are going to be branches going out called muscular branches. So the muscular branches
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are gonna supply primarily the lateral, deep and craniothoracal groups of the neck; So it’s gonna
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innervate the rectus capitis lateralis, rectus capitis anterior, longus capitis, longus coli
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muscles, scalenus anterior and scalenus medius as well. So, all of these muscles are gonna be
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innervated by the cervical plexus through the, muscular branches. Coming from C1 through C4.
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Awesome. The next thing that’s gonna happen
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is that the C3 and C3 are gonna extend outwards, and then come together. When they come together
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they’re gonna form what’s called the inferior root of Ansa Cervicalis.
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Another thing that’s gonna happens, is that the 12th cranial nerve, the hypoglossal nerve
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is gonna go alone the superior side of C1, as it goes towards the tongue to innervate the
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extrinsic and intrinsic muscles of the tongue. So C1 is gonna follow the hypoglossal nerve,
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and then give off the superior root of Ansa Cervicalis.
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So the superior and the inferior root are gonna come together and form a nice little loop. And
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that loop is called Ansa Cervicalis. And it’s a very important look, why is it important.
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It’s important because it’s gonna supply specific infrahyoid muscles.
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So it give off 4 different branches. And these have to be in a special order
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from superior to inferior. I’ll just draw 4 lines like this, but the left one is supposed
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to be superior, going inferiorly towards right. This order is important because there can actually
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be some kind of lesion that can affect some of the muscles and not the others.
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Alright so what are these branches? So the most superior one, the first one is going to
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be the Omohyoid muscle. It’s an infrahyoid muscle so it depresses the hyoid bone.
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Then we got the Sternothyroid, which depresses the thyroid cartilage.
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We got a branch that innervates the sternohyoid, and another one that innervates the inferior
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belly of the omohyoid. If you guys are unsure about the functions of these muscles, I have a
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playlist for the muscular anatomy if you wanna refresh your knowledge in that specific topic.
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Alright. So that’s Ansa Cervicalis, the Cervical loop, or the deep
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cervical loop is actually what it’s called. Now. The 12th cranial nerve, the hypoglossal nerve
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is going to go to the tongue, right? Innervating the intrinsic and extrinsic muscles of the tongue.
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C1 is going to give off two branches, specifically for the geniohyoid muscle, which elevates the
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hyoid bone. And the Thyrohyoid muscle which is actually going to depress the hyoid bone,
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but elevate the larynx. Awesome. We’re almost done now.
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We talked about the Somatosensory branches. We talked through the motor branches,
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which consists of the muscular branches coming from C1 through C4, and the ansa cervicalis,
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formed by the inferior root from C2 and C3, and the superior root from C1. Some sources might
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say that the superior root come from both C1 and C2 because of the connections between C1 and C2.
Mixed Nerves of Cervical Plexus
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The last branch is a mixed branch. What happens is, coming from C3 is a nerve called the phrenic
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nerve. On it’s way down to the diaphragm, it picks up branches from C4, as well as C5.
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Technically the cervical plexus is only C1 to C4, but C5 is also important because
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it gives off this branch here. Now.
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If you look here, we have the C3, C4 and C5 roots coming together to supply what?
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All of this will give way to the most important nerve of all this is the phrenic nerve.
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Phrenic nerve is one of the most important nerve and the reason why is because it
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supplies the main muscle of inspiration. It’s the Diaphragm. So it supplies the diaphragm.
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Any type of damage to the C3, C4 or the C5 nerve root it can cause extreme damage it can cause,
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if this isn’t able to work, you can actually have respiratory arrest, or respiratory
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failure. You won’t be able to inhale anymore. Notice that this is a mixed branch. Now what
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that means is that the phrenic nerve contains motor fibers. It contains sensory fibers,
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and it contains sympathetic postganglionic fibres. And the reason why is because it has branches
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that supplies some other structures aswell not just the diaphragm,
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so let’s go through the branches of this one. So again this nerve goes down, and give a
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phrenic branch, which provide motor innervation for the diaphragm. So the left and right phrenic
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nerves innervate their corresponding ipsilateral hemidiaphragms. And this is the only motor branch.
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The other branches are sensory branches. So it gives off pericardial branches that provide
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somatosensory innervation for the pericardium It has pleural branches, providing
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somatosensory innervation for the mediastinal and diaphragmatic pleura
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It has phrenicoabdominal branches providing somatosensory innervation of the parietal
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peritoneum under the diaphragm, down to the gallbladder and pancreas.
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And it has sensory branches for the thymus. The sympathetic postganglionic fibres
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engage the diaphragm to a sympathetic response. So fight or flight response.
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Alright. So that is really all the branches of the Cervical
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Plexus that I wanted to include in this video. But now what I’m gonna do is that I wanna include
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one more mini diagram because we have to talk about one more relationship,
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and that is the relationship with the accessory nerve. The 11th cranial nerve.
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Now we gonna talk about this in detail when we start talking about the cranial nerves
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individually, but for simplicity let’s add the spinal cord and the brainstem.
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Alright so first things first, the main motor nucleus of the accessory nerve
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is located within the medulla. In the medulla there’s a special nucleus called Nucleus Ambiguus.
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So the nucleus amiguus is a very very important nucleus because from the nucleus
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ambiguous, you’re gonna actually have the Glossopharyngeal nerve coming out of this.
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You’ll have the Vagus nerve come out of this. And even, the accessory nerve, but very very specific
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here. The accessory nerve, the cranial part of it. So there’s a cranial part of the accessory nerve,
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and there’s a spinal part of the accessory nerve. So from the nucleus ambiguous, the cranial part of
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the accessory nerve is going to emerge, and it’s then going to go through the jugular foramen.
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What happens now is that most of the fibers from the cranial part of the accessory nerve
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is going to go with the 10th cranial nerve, the vagus nerve to supply a lot of the pharyngeal and
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laryngeal muscles, right? But some fibres are going to continue without branching.
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So what about the spinal part now? If we highlight the spinal cord
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segments C1 through C5. There’s something very interesting that happens.
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If we take one segment out, so we’re looking at a cross section of one of these segments here.
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And I look at this. And you know that when you’re looking
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at a cross section of a spinal cord you know that you have the anterior gray horns, right? Which is
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the cell bodies of the somatic neurons. Here’s the posterior gray horn with the
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cell bodies of the sensory neurons. Then over here we’re gonna have the
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lateral funiculus. And then we’re gonna have the anterior funiculus, or the anterior white column.
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And then we have the dorsal white colum, or the dorsal funiculus.
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Something very strange happens within this part of the cervical region of the spinal cord. Coming
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off the lateral funiculus. You’re gonna have those fibers coming outwards and then moving outwards.
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What happens is, the lateral funiculus of C5 is going to gives off a branch that
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traverses upwards. The lateral funiculus of C4 gives off a branch that traverses upwards.
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The lateral funiculus of C3, C2 and 1 gives off branches that traverse upwards.
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Now, why is this important? Out of this, if you remember
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coming off of the anterior Gray horn, you’re gonna have the anterior root of the spinal nerve,
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and from the posterior Gray horn you’re going to have the posterior root coming out of it.
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Going together forming the spinal nerve. Why is this important?
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This little cord that you see coming up here from C5 up to C1. That cord right there that’s running
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in between the anterior root and the dorsal root. This is called the lateral funiculus.
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So as it moves upwards, it’s going to meet up with the cranial part of the accessory nerve,
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to go through the jugular foramen. And when the cranial part of the accessory nerve,
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the remaining fibres of it, meets up with the spinal part of the accessory nerve, which
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comes from the lateral funiculus. When they meet up, they form the main accessory nerve.
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Now what happens, is that from the anterior ramus of the spinal nerve,
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you’re going to see some branches that emerge from C2, C3 and C4. So the anterior ramus of C2,
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C3 and C4, which is a part of the cervical plexus. They will give of branches that join the accessory
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nerve to then go to two destinations. One of the destinations is towards the trapezius muscle. And
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the other one will go to the sternocleidomastoid. This is a very simplified scheme of the accessory
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nerve. We will talk about the accessory nerve in detail in a separate video.
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So that’s the relationship I wanted to talk about. It’s the relationship between the cervical plexus,
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and the accessory nerve. The 11th cranial nerve. Awesome.
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So that was everything I had for the Cervical Plexus. The next
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video is going to be about the Brachial Plexus. I really hope you found this video helpful. If you
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did, please put a like, comment and subscribe. See you next time.
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