Today we're going to talk about Neck Muscle and answer the questions of what muscles are found in each plane to the cervical fascia.

What are their actions and innervation? And what's the deal with the different layers of muscles? Hello, everyone. My name is Dr. Morton and on the noted anatomist. So my approach for this is going to be covering the muscles based upon their location in the cervical fascist. So we see this cross-section through the neck. 

And so we'll cover the muscles in the superficial and in the deep investing, and in the prevertebral

and in the pre tracheal fascist. 

So let's start with the superficial fascia and the platysma muscle. So here's a cross-section of the neck around the C six vertebra, and there in red is the platysma muscle which is in the superficial fascia or hypodermis.

And so from this lateral view, there's our patella muscle and it's going to come from the corner of the mouth and the angle of the mandible all the way down to the sternum and clavicle and that fascia over the PEC major in the deltoid, and so the platysma muscle wrinkles the skin of the neck. The skin of the neck is shown in that red diagram where the patella is. And the innervation is via the facial nerve cranial nerve number seven, 

and so there's cranial nerve seven right after it comes out the style of mastoid frame and it comes down to the cervical branch innervates the political muscle it's the only muscle I think really that the cervical branch of the facial nerve innervates. So we've covered the muscle and the superficial fascia. Now the deep investing fascia, which includes our sternocleidomastoid, and trapezius muscles, sternocleidomastoid, or sem, and trapezius, let's start with sternocleidomastoid, which is named according to its attachments. And so there we have the sternal attachment, clavicular attachment and Kaleido means clavicle, and the mastoid process, hence sternal Kaleido mastoid. 

And the sternocleidomastoid turns the head to the opposite side and it flexes the neck on the same side. So here we have the sternocleidomastoid on the left, and when it contracts, it turns the head to the right. And so the left sternocleidomastoid causes you to look over your right shoulder, that's one action. Also, it has a unit, the sternocleidomastoid flexes the neck on the same side so the right sternocleidomastoid flexes or bends the neck on the right side like that.

And the trapezius muscle elevates the scapula or shrugs the shoulders and so there's the trapezius muscle from the side. 

And there it is from the front superimposed on this model and you see the traps elevates the scapula or shrugs the shoulder it does other actions but that's covered in greater detail in the back muscle. So the scapular elevation of the shoulders and the other big one is the extension of the head and neck things that you see the head and there we have the head that's flexed and the trapezius muscle extends the head and neck from here to here.

We're next going to talk about the innervation of this SCM and the traps which is through cranial nerve 11 the spinal accessory nerve. In this lateral view, we see the spinal accessory nerve there within the post your triangle the neck, the spinal accessory nerve exits through the juggler frame and then gives a nerve innervation to the sternocleidomastoid courses across the post your triangle, the neck and innervates the trapezius muscle, 

the deep investing fascia, now we're going to the prevertebral fascia muscles. And so those include the scalene muscles, the anterior middle and post your scalene muscles and then this cross-section there's anterior middle and post your scalene muscles and Shin cervical and brachial plexus see exit between these anterior middle scalene muscles. 

Now let's look at an anterior view. There is our anterior scaling our middle scaling in our post your scaling muscles and up high you can see the phrenic nerve, a branch from the cervical plexus exit in between anterior and middle, and then there's the brachial plexus exiting as well between the anterior and middle scaling. So this term scalene is Greek for uneven because the inter middle and post your scalings are all different lengths. 

Now let's do a small detour. The trunk consists of the neck, the thorax, the abdomen, and the pelvis. And then you have the head on top and the two limbs upper and lower limbs. But the trunk is these three things. So the abdomen in cross-section, we notice the following. 

There's the external oblique, the internal oblique, the transverse abdominous muscles, and then the lumbar and intercostal nerves course between the internal oblique and transverse abdominous. Now let's take a look at a cross-section through the thorax there's the external inner coastal internal

frontal intercostal and innermost intercostal muscles and look at the intercostal nerves course between the internal innermost intercostals. Now let's look at a cross-section through the neck. 

So the poster you're scaling, there's the middle scaling, and there's the anterior scalene muscle and the cervical and brachial plexus these exit between the anterior middle scalings. So the take-home point for this is the following. The anterior lateral trunk wall has three layers of muscles,

and the nerves and vessels course between layers two, and three. The neck, the thorax, the abdomen, and the pelvis all work in that way. So back to the scalene muscles, they elevate the first and the second ribs. And so here we have the scalene muscles. And you see when they contract they elevate that first and second rib that helps to increase the diameter of the thoracic cavity which increases the volume of the lungs that helps you inhale. 

Then you also have lateral flexion of the neck. So when you look at this view, and you see there's the post your triangle the neck because it's between the traps and the sternocleidomastoid and the muscles that form part of the floor, or the scalene triangle of scalene muscles form part of the floor of the poster triangle and they bend the neck to the same side lateral flexion of the neck.

The scalene muscles are innervated by branches from the C four to C eight ventral Raima. So here's a picture of the brachial plexus and labeled c five two-tone. 

I don't have C four on here, but branches coming off of the eventual rain my from seeing 4567 and eight are going to then go and innervate the scalene muscles levator scapulae elevates the scapula shrugs his shoulders and there are the levator scapulae in this cross-section. 

And there it is here in this posterior view. Again, this muscle even though we find it in the floor of the posterior triangle, the neck, and its part of this in this prevertebral fascia. It covers in more detail the upper limb scapular link scapular sling content. Now the longest capital and longest Kol eye muscles and here in this anterior view There is our longest capital this word longest as its name indicates is a long muscle that attaches to the head capitis like a baseball cap.

 And then there's the longest co lie long muscle in the CO lie which is BVH EDM ology is the neck, long muscle attaches to the head, long muscle on the neck and it's there in the cross-section. These muscles are important for Topock topographical but functionally not as much. There's some little bit that can be done if, during whiplash, they can get injured, but for the most part clinically is just nice to know it's good to know where they're located. So muscles in the prevertebral fashion now muscle in the pre tracheal fashion. This includes the infrahyoid muscles, the sternal, hyoid thyroid omohyoid, and thyroid muscles. 

Who there is our sternal hyoid, our sternal thyroid, and our omal hyoid muscles. Now let's take a look at them from an anterior perspective. And to do that, this is you're looking at someone and their chin. They're looking up at the ceiling. There's the hyoid bone, there's thyroid cartilage or your laryngeal prominence, and there is the sternum. And so when you look at the muscle, the arrow and you think what's the name of that muscle and Animas said bullet goes from the sternum to the hyoid. Let's call it the sternal highway muscle. But wait, what about this muscle? Well, let's going from the sternum to the thyroid cartilage. We'll call it the sternal thyroid muscle but what about this one? It's going from the scapula or shoulder which is the abbreviation for the hyoid bone, we call it the omohyoid shoulder to highway muscle. 

And what about this one that's going from the thyroid cartilage to hyoid viral hyoid muscles. And so the actions of these muscles are simply not simply what they help depress in support the hyoid bone so when you swallow the hyoid bone goes up, it helps to bring it back down. These are postural muscles with the hyoid and to the extent the laryngeal prominence that thyroid cartilage clinically, it's not like you're going to be testing these muscles.

They're innervated by the cervical plexus, specifically, the answer serves a callus. 

So here's the cervical plexus from C one to C five. And in yellow is the answer server health that has a superior limb that comes from C one and an inferior limb that comes from C two and C three ventral Raima. And so what happens is we see off the superior limb there's a nerve to the Federal Highway in the genius Ohio aid. It's above the highway bone, a nerve to the omohyoid to the superior belly, a nerve to the sternal thyroid the nerve to the sternal hyoid, and then a nerve to Ohio the inferior belly. Basically, I showed them all here but really if you know that these infrahyoid muscles are innervated by the answer serve a callus clinically that's sufficient. Okay.

There we have it. So why are both somatic? Body wall muscles in Brinkema large muscles found in the neck. So here in this cross-section take a look there are our somatic body wall muscles and what I mean by that they're derived from the so might so there's Stern, Ohio external thyroid or normal hyoid. 

And then there's our scalenes levator scapula, and also the abaxial muscles, the paraspinal muscles, and the brachial arch muscles like droplets visma, from the brain to large number two in the sternocleidomastoid and traps from the hind arches. So what's the deal? Why do we have this? Well, the answer to this question we say the head and neck are like an orange on a toothpick. funny movie. So there's an orange and there's a toothpick. So watch what happens. It doesn't look very stable and thumps. That's what would happen. Okay, we just dropped so even if we go let's push this back up, and you let go, it drops. So you push this back up and it drops. So what do you do to stabilize this orange? 

Well, let's put some, maybe some bungee cords in the back like this and tighten them. See that you tighten in it goes up? Well, the head neck is like an orange on a toothpick. You have an orange and you have a toothpick. So then it falls over you put some bungee cords we call them the sternocleidomastoid in the traps, and they do this they bring the head up because the sternocleidomastoid in the trapezius are both hind arches that are basically coming from the head and they migrate down. And so what happens is you've got these Semitic muscles here like those infrahyoid and the scalenes. those muscles, for the most part, attached to and from within the neck, they don't go to the head so the head would flop forward so that we have these brain large muscles like sternocleidomastoid and traps that migrated down to the shoulder into the back to help stabilize this orange the head on the toothpick, the neck and that my friends are the muscles of the neck in a nutshell.

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