Okay, this video is going to take you guys through the muscles of the head and back. So as we would with any new model, the first thing we need to start off with is orientation. Luckily for us, most of us have looked in a mirror, so we know that our faces are located on the front of our head.
Okay, so if we look at this model like this, this is going to be the anterior view. We also have a lateral view, which you'll remember is a view from the side. This is one side of the model. This is the other side of that same model. And then this would be a posterior view or the view from the back.
Okay now something else that you should note about this model is if you look at the face it doesn't look exactly symmetrical and that's because the each side kind of shows something a little different. So this side here on the face this is the more superficial side of the model. So this is going to show muscles that are closer to the skin so closer to the surface of the body. This side of the model is a deeper side.
So a lot of times with our deeper sides of our models that depict muscles, a lot of these more superficial muscles have to be cut and removed in order to see this deeper side. Okay, so if we want to name some of these muscles, we have to kind of keep in mind that a lot of the root words are going to be coming from our Latin and Greek root words. So although they might sound a little odd at first, they actually make sense when you start to understand what some of these roots are referring to. Okay, so we're going to move through this model, superior to inferior, and we're going to hopefully stick with superficial to deep, although we might kind of deviate a little bit from now and then. So let's go ahead and get started with this muscle that's right up here on the top.
So you guys might not be able to see the full thing right now, you can only see one part of it. Okay, If we were to select this whole area here, lift the model and show you this whole white space up here on top of the head, and even show you a posterior view of that same model, all the way back here, you can even see there's some more muscle back here. That's all one connected piece. So all the way from the front of the forehead to the back of your skull is connected by one muscle. And that muscle is called the epicranius.
Okay, the epicranius. Epi is a prefix meaning on or upon. So sitting on top of the cranium, epicranius. Okay. It also does have another name, which is occipitofrontalis.
Okay, occipitofrontalis. And that is coming from the two points of attachment. So we have an occipital belly here, which is on the back of the head. And you guys will remember that occiput.
is referencing the back of the head. That's why we have the occipital bone. Okay, so we have the occipital belly back here.
Okay, and then if we were to rotate this around to that anterior view again, right, we can see the frontal belly here. Okay, so that's the frontal belly sitting on top of that frontal bone of the skull, and that's where that term occipitofrontalis comes from. Okay, now we did reference that white part kind of connecting the two bellies.
That is called the Galea Aponeurotica. The Galea Aponeurotica. Galea is actually a term that we use to describe some of the helmets that were worn in the military forces in the Roman times.
So basically, it's something that you would put on top of your head. So Galea is referencing a helmet, and then Aponeurotica is referencing an aponeurosis, which is like a thick, fibrous connective tissue. So it makes sense that this white tissue that's connecting the two muscle bellies is called the galea aponeurotica.
Now as we move down onto the face, the first muscles I see that kind of stand out to me are these rings around the eyes. These rings here, there's one here and one on the other side as well. These are called the orbicularis oculi muscles.
The orbicularis oculi muscles. Oculi, of course, is referencing the eye and orbicularis is referencing the shape of that muscle. And you'll notice it's circular in shape, kind of like an orbit. Okay, so orbicularis oculi is surrounding the eyes, one on each side.
Okay, you can see that on this side, on the deeper side, there is a muscle that's kind of like peeking out here. We cut away a little bit of the orbicularis oculi so we can see something underneath. That muscle is referred to as the corrugator supercilii or corrugator supercilii. Okay so the corrugator supercilii or corrugator supercilii. Okay, now this muscle will help that brow to kind of get pulled in medially and forward.
So if you're kind of squinting at someone, that muscle is definitely contracting and engaged in that expression. Okay, so this one we sometimes say that if you're going to make a silly face, you have to use your corrugator super silly. Now between the two orbicularis oculi, there's also a muscle that sits right here on the forehead.
kind of between the eyebrows. So right on top or superficial to that glabella of the skull that we learned about. Okay so superficial to the glabella. We have this muscle here that pulls the eyebrows in immediately.
So if you're trying to frown and pull the corners like the medial corners of your two eyebrows in, okay, we'll be using this muscle. And this muscle is called the procerus. Okay the procerus. That's the muscle that is superficial to the glabella. Don't confuse the two.
The prosterus is a muscle. The glabella is on the skull. So just to recap, we've had our epicranius or occipitofrontalis. That was on top of the head.
Right. The two bellies are the frontal belly and the occipital belly, which is on the back of the head. And those were connected by the galea aponeurotica. As we come down around the eyes, we have the orbicularis oculi muscles, one around each eye.
And deep to that orbicularis oculi, we have the corrugator supercilii or corrugator supercilii. Between the eyes, by the medial corners of the eyebrows here, superficial to the glabella, we have the proseris. Okay, the proseris. Again, that's going to draw the medial edges, so the insides of your eyebrows, together. So this happens a lot when you're frowning or making a very serious face.
So you can remember that your procerus is procerius, right? That's the procerus muscle. All right, as we move on down to the face, the next muscle I want you guys to know is on the sides of the nose.
Okay, so if we look here, we're going to turn this a little bit. On the side of the nose here, we have a small muscle called the nasalis. Right here, this is the nasalis.
And that makes sense because anytime we hear nasal, we think of the nose. Okay, the nasales. If we progress down to the muscles that are going to be moving the mouth, you'll notice we're going to have a lot of those.
Okay, that makes sense because we use our mouths for a lot. We use them to communicate, we use them to eat, so we need to be able to move our mouths to make facial expressions, to help move our lips to obtain food and keep the food inside of our mouths while we're chewing. There's a lot that we're doing here. Even when we're just forming different sounds with our mouths as we communicate, we need a lot of different muscles to help to make a specific shape of the mouth that will create the sound that we need.
OK, so it's going to be a lot of muscles in this area. If we come across on the lateral side here on the superficial side of the model. OK, the first muscle that you're going to see is this muscle right here.
Okay, and this is going to be the levator lay-by. superioris. The levator labi superioris.
And if we break down the words in the name of that muscle, levator is because if we look at where this muscle is, if it contracts or gets smaller, it's going to pull the lips up. So it's a levator because it's pulling that lip up. Labi is of course referencing the lips.
and superioris because this muscle is located superior to the mouth and will be acting on the top lip. Okay, so levator levi superioris. A lot of students will abbreviate this one as LLS, a levator levi superioris. As we move down, we have a pair of two muscles here that run parallel to one another, and these are actually sitting right on top of our cheekbone from the skull do you guys remember what that dome was called Yes, the zygomatic bone.
Okay, so these muscles are sitting right on top of the zygomatic bone. So we call them the zygomaticus muscles. Okay, zygomaticus. Now we can't call them both zygomaticus.
We have to find a way to differentiate between the two. So this one that's a little bit smaller and more superior is going to be the zygomaticus minor. The zygomaticus minor. This is smaller and more superior.
So it's the zygomaticus minor. The larger of the two, which is a little more inferior, is the zygomaticus major. The zygomaticus major. And you'll see that a lot in the body. We have two muscles that run together parallel to one another.
A lot of times the one on top will be a little bit smaller and will be named minor. And the one that's on the bottom will be larger and will be named major. So this is your first pair that you're going to see like this, but you will see more throughout the course.
All right. Now, as we move down the cheek, we can see another muscle here that kind of goes from the corner of the mouth back toward the cheek. If we turn the model, we might be able to see the whole thing. There we go.
Okay, this muscle here is called risorius. Risorius. And there's a lot of ways to remember this one, but my favorite one is I think of risar, to laugh, and it almost looks like a smile on the face. Okay, I've never really seen anyone laugh while frowning, so this just makes me think of smiling and laughing together, the risorius.
Now all the way back here we have a very large superficial muscle. This is going to be called the masseter. The masseter.
The massive masseter. This muscle is going to actually be important in mastication, which is chewing. We're going to have a few muscles that we need to know for that process and so we will come back to this one shortly.
But for now it is just the masseter. If we go back... to the anterior view.
Okay, let's just quickly run through what we've seen so far. All the way up here at the top, we had levator labi superioris, right, our LLS. We had zygomaticus minor and major hanging out together, superficial to that zygomatic bone of the skull. We also have the risorius muscle here, the risorius muscle helping us to smile. And then all the way on the side here we have the masseter muscle.
Okay, that is very superficial. We're not going to be able to see a lot of these more superficial structures on the other side of this model. All right, now if we come down here kind of below the mouth you can see a triangular-shaped muscle right here which is called the depressor anguli oris.
Okay, depressor anguli oris. Let's put our thinking caps on. Why would that be the name of this muscle? It's telling us where it's located and what it's going to do.
We said that this was a levator because it pulled the lip up. By comparison, this is a depressor because it's going to pull the lip down, okay? So it's depressor anguli oris because we are connecting at the corner of the mouth and we can actually pull both lips at the corner here down towards the jaw or down toward the mandible. Okay, so this would be really helpful if we're trying to make a frowny face.
Okay, so that's the depressor anguli oris. This one was labi, we'll remember, because it's attaching, excuse me, directly to the lip, whereas the anguli is going to the corner of the mouth. Okay, so that's the difference between those two, other than their location and their action. All right, now if we go over to the deeper side. Let's say we kind of cut this muscle away, our levator labi superioris, and our depressor anguli oris.
We're going to see two other muscles that are going to be acting on the lips. One is right here, visible in this cutout. That's going to be the levator anguli oris.
The levator anguli oris. Okay, so just like the depressor that we saw on this side, this muscle is also attaching to the corner of the mouth. so it can pull both lips up back toward the cheek like this.
It looks like you're going to smile. Okay so that is the levator anguli oris connecting at the corner of the mouth. Okay our next muscle down here we can see because we've removed the depressor anguli oris on this side, this is going to be our depressor labi inferioris. Our depressor labi inferioris. So this one is actually named similar to this one over here, right?
Because we had levator labi superioris. Now we have depressor labi inferioris. This is telling us what it's doing, what it's doing it to, and where it's located.
So it's a depressor because when this muscle contracts and gets smaller, it's going to pull down at the lip, not the corner of the mouth. The lip is a hole. So depressor. labia, lip, and inferioris, because not only are we attaching to the bottom lip here, but we're also below the mouth.
Okay, so just to kind of... recap what we had on this side. On the nose, we had the nasalis, right?
Then we came down to levator levi superioris, our zygomaticus minor and major, risorius, masseter, and then this one down here is depressor anguli oris. If we wanted to find the levator anguli oris, we have to go diagonally across the mouth because it is deep to the levator. But the levator is over here. So this is the levator labi superioris. This is levator anguli oris.
This is depressor anguli oris over here. And if we cut that away, we could see depressor labi inferioris. Honestly, with these as a student, I didn't love them. I found them to be really hard to remember.
But if you just make like a crisscross across the face, it might help you remember how these are labeled on the model and how they're visible. Now keep in mind all of these models on your face are bilateral, which means they exist on both sides. But you're not going to be tested on your face, you're going to be tested on this model. So what's a trick that can help you with these?
So what I mean by that is if you draw an X kind of across the face like this, these two are named similarly and these two are named similarly. Okay so these two are the anguli oris. These two are the ones with labiae in them, right? So we have labator labi superioris up here, depressor labi inferioris down here, okay?
And again, all of these muscles are acting to manipulate the face, to manipulate the mouth so that we can speak, so that we can eat, and so we can kind of communicate using facial expressions, okay? So all these muscles are going to be really important. Now, you'll notice that there are some connection points surrounding this muscle here. And this muscle is going to be named similar to what we saw around the eye. So do you guys remember the term that we used for this circular shaped muscle?
Not oculi, right? That was referencing the eye. What was the other term that we used?
Orbicularis. Okay, orbicularis, like an orbit. Okay, this muscle is going to be called orbicularis oris. Okay, orbicularis oris.
This one going all the way around the mouth. Oris, of course, is referencing oral, by mouth. So we had orbicularis oculi here and oris down here.
The last muscle that's on the front of the face that we need to cover is this one down here on the chin. And this is called mentalis. Mentalis. That comes from the Latin root mental, which is referencing chin. So if you go back and look at the mandible, right in that front portion where we would call the chin.
You see a lot of terms that have mental in them, like mental symphysis, mental foramen, mental protuberance. Mentum is chin in Latin. Okay, so that's where that mentalis is coming from. All right, one more time through those.
We had the levator labi superioris, depressor labi inferioris, depressor anguli oris. And then in this cutout up here. Okay, we can see levator anguli oris. This one around the mouth here is orbicularis oris.
Orbicularis oris. And then this one down here on the chin, that's mentalis. Okay, mentalis. All right, let's go to the deep side over by the cheek. This view is going to give you a great look at the rest of those muscles of mastication.
So I did mention one earlier that was very superficial on the cheek, which was the masseter. That is one of four muscles of mastication. It's one of four.
Your other three are going to be visible on this view of the model. So the first one is this one here that's going to be up on the temporal bone. That's temporalis.
That muscle is temporalis on the temporal bone. this whole muscle here okay That one would make sense for me as far as being a muscle of mastication because I don't know if any of you guys chew gum or even if you're just eating of course you're just chewing. You will notice that your temples are kind of moving right they move kind of in and out that's because this muscle is contracting and relaxing to help us move the jaw. Okay so that is the temporalis muscle that is your second muscle of mastication.
If we look down here in the cheek we'll see our other two muscles of mastication. So we have one here. and then one down here.
I know it's a little tough to see the difference between the two, but we do have one that's coming kind of from this corner here down, and then one that's coming from here up like that. Okay, now these are called the pterygoid muscles. The pterygoid muscles, and that's pterygoid with a PT, like pterodactyl, okay? And these are referencing kind of the pterygoid plates that we see on the base of the skull, and medial and lateral is kind of referencing their points of origin and insertion with respect to one another, okay?
So it's not as intuitive to look at these muscles and say one is medial and one is lateral because they do look like at this point they're stacked on top of one another, right? So the way that I remember this is up on top here we have the lateral pterygoid muscle. This is the lateral pterygoid muscle. This one down here is the medial pterygoid muscle. And I just remember them being in alphabetical order.
So in the alphabet, L is right before M. Lateral is on top of medial. Okay, so there's your trick for that.
So if I wanted to list all of my muscles of mastication, they would be the masseter, the temporalis muscle, and then the lateral and medial pterygoid muscles. That is something that I would definitely recommend knowing for not just your assignments, but also your exams. Those are your muscles of mastication. Another muscle we can see here while we're still in this view, it's a deeper cheek muscle. Don't confuse this with masseter.
This is the bucinator. The Bucinator is in place. for drawing the walls of the cheeks in toward the teeth.
So let's say we're gonna blow a bubble. Okay, if you're chewing gum and you go to blow a bubble, when you make that blowing action, you're drawing your cheeks in toward the middle of your mouth, right? That's gonna be a bucinator.
Okay, now this little yellow circle right here is actually representing a duct in the cheek, okay? And that duct is coming... from a gland and heading inward toward the mouth. Okay, so you guys will learn in block three that we have a salivary gland that sits kind of out here really superficial on the cheek.
That's called the parotid gland. Okay, the parotid gland. And then a duct comes from this gland, crosses through that buccinator muscle, and goes inside of the mouth.
That makes sense because we don't want saliva to just be deposited in our muscles inside of our cheeks, right? We need it in our mouths. So the gland is really superficial in the cheek, okay?
And then the duct moves inward toward the mouth, okay? So we call this duct either the parotid duct, which makes sense because that's the gland it's coming from, or we can also call it Stenson's duct, okay? The parotid duct. or Stenson's duct.
That's this little yellow circle right here. That is going to transmit saliva from the parotid gland into the mouth and it's going to empty out into the mouth at the level of the upper second molar. At the level of the upper second molar. All of our salivary glands do eventually have to empty into the mouth.
As I mentioned, we want saliva going into the mouth nowhere else. but this is the specific point at which the parotid gland saliva will enter into the mouth. And again, that is the upper second molar.
Okay, just to review these one more time, again, we do have three of our four muscles of mastication that are visible from this point of view. We have the temporalis, which is up on the temporal bone, right? We have the lateral and medial pterygoid muscles. Hey, remember lateral is going to be on top because L comes before M in the alphabet. here's medial down here.
This muscle was the bucinator, the bucinator that helps us blow bubbles. And then this was the Stenson's duct or parotid duct. And this is transmitting saliva from that parotid gland medially inward toward the mouth and delivering that at the level of the upper second molar. So once we went over those muscles of the face, and the top of the head, you can really categorize those into two different kind of groups, okay? Most of what we saw here are muscles that help us to control our facial expressions, okay?
So it helps us make, you know, a face like we're smiling or we're frowning or we're angry, so it manipulates the face into a way that we can express how we're feeling, okay? There is a group of entertainers that are well known for doing this because they can only communicate using their facial expressions in their bodies, and those are minds. So any muscles that we really use to just kind of control our facial expressions are called mimetic muscles of the face. a memetic like mine, right?
And I'll just tell you guys, I'm going to spoil it for you. Pretty much every muscle that we covered on the face was a memetic muscle. The only muscles that I would not include in that would be our muscles of mastication, okay? And if we go back, remember we can see one here that was very superficial.
Do you guys remember what this one was called? Yeah, that's the masseter. Very powerful muscle, okay?
Very superficial. That's the masseter. And if we wanted to find the other three muscles of mastication, we have to go to the other side of the model, right, which is the deeper side, and that's where we would find that temporalis, okay, and the lateral and medial pterygoids. So those are the two groups of muscles that we find on the face, and that is significant because it also helps us to remember the innervations for these muscles. Now if you're still a little confused on this, just remember that an innervation just means what nerve tells this muscle to contract.
So what nerve is making this muscle move? For all of our mimetic muscles, so to give you a few examples, things like the levator labi superioris, the nasalis, the orbicularis oris, the levator anguli oris, all of those muscles are innervated by the same nerve, and that's going to be cranial nerve 7 for the facial nerve. And I guess that would make sense when you think about the name of the nerve.
Okay, so cranial nerve 7, the facial nerve, will innervate all the memetic muscles of the face. And again, that's pretty much everything we've covered so far, except for our muscles of mastication. For our muscles of mastication, we will have a different nerve telling those muscles when to contract.
And that nerve is actually a branch of cranial nerve 5. okay cranial nerve five is the trigeminal nerve cranial nerve five is our trigeminal nerve and we're specifically looking at branch three which is the mandibular branch okay so if we ask you on an exam what nerve innervates the muscles of mastication right you could say any of the following trigeminal nerve branch three trigeminal nerve mandibular branch or mandibular nerve. Any one of those three and we will know what you're talking about. Okay, so any one of those would work.
All right, that's pretty much it for the face. Now we just need to talk about the neck. Okay, so I'm gonna tilt the model up so we can get a better look at this.
Statistically speaking, this is probably the area of the model and of this block that students struggle with the most. And I happen to think that it's partially because these are a little hard to see. but also because I think maybe sometimes students see things like the skull and the brain and they think oh I really have to focus on those and they don't spend adequate time on this model especially when it comes to the neck. Okay so please please please do yourself a favor just make sure you spend some time with this model whether that be in the library or in lab office hours it is definitely the area that could be improved upon the most by the general students to take this course, okay? All right, so we're going to start with muscles that we can categorize generally as suprahyoid muscles.
Suprahyoid muscles. And the reason why we call them that is because we have a bone here called the hyoid bone, okay? And these muscles are going to be superior to the hyoid bone, okay?
Now muscles in this area are really easy to name when you get the hang of this. because there's a lot of root words or prefixes and suffixes that just kind of reflect where these muscles attach to. Okay, and I'll give you a few examples as we go along.
Again, this part of the model is also not symmetrical. It's asymmetrical because we have a superficial side, okay, and a deep side, right? This superficial side shows a few muscles.
The deeper side shows the muscles if we were to cut these away, right? So just keep that in mind. if we look at the superficial side first.
The most superficial of these muscles that we can see are going to be things like the digastric muscle. So the digastric muscle starts here, comes down like this, and then comes back here, kind of almost up toward the ear. It's really going towards the base of the skull.
So we have one part of the digastric here and then coming back like this as well. Digastrin. means two bellies, and that's what we're seeing here.
We're seeing two bellies of muscle that are connected. So we have one here, that would be the anterior belly of the digastric muscle, or you can also call that the anterior digastric. the anterior belly of the digastric muscle or the anterior digastric.
And then back here, if you look, there's two muscles that are kind of stacked on top of one another. The posterior portion of that digastric muscle is the bottom one. Okay, so this muscle right here would be the posterior belly of the digastric muscle, or you could just call it posterior digastric. Just above that right here, this muscle. is going to be the stylohyoid muscle.
Okay, the stylohyoid muscle. Remember how I said a lot of these muscles are kind of easy to name because of the roots? Okay, so stylo is referencing something on the base of the skull. You guys think of something down there that would have stylo in it? Yeah, the styloid process.
Okay, so remember the little one that looks kind of like a DS stylus coming off the base of the skull? Okay, so this muscle, the stylohyoid, is going from the styloid process on the base of the skull down to the hyoid bone. Okay so this right here would be that stylohyoid. The way that I remember which it is of these two muscles here is I just think of stylohyoid is stacked on top.
A stylohyoid is stacked on top because who doesn't love alliteration? Okay do you guys remember what this muscle here is? What is stylohyoid stacked on top of? Yeah, that's the posterior digastric. Posterior digastric, right?
Now, if we were to remove all three of those muscles, we would see one muscle that kind of covers this whole area, almost like a sheet, okay? So it's one big muscle that covers this whole area between the mandible and the hyoid bone, like a blanket or a sheet, okay? So if I cut this away, you guys see all of this right here and all of this right here.
That's all one muscle. and that muscle is called the mylohyoid. And the mylohyoid. Myo is referencing, or mylo, excuse me, is referencing the mandible. Okay, so this is the mandible right here.
And then hyoid is of course referencing the hyoid bone. Okay, so mylohyoid. All right, that's pretty much everything for this superficial side.
Okay, so we have the mylohyoid, which is the blanket, right? We have the two bellies of the digastric. This of course would be anterior because it's closer to the front of the body. This would be the posterior digastric back here.
And then remember our stylohyoid is stacked on top of the posterior digastric. Okay so that is our superficial side. Now if we were to cut all of that away, okay so the anterior digastric and the mylohyoid have both been removed here on this view, you can still see things like the posterior digastric and the stylohyoid back here.
If we remove the blanket, what do we see underneath? This muscle here that kind of hangs out really close to the midline, this is going to be the geniohyoid. The geniohyoid.
The prefix genio means chin. So we're going from the chin to the hyoid bone. This muscle is deep to the mylohyoid, but it's different from it because it only exists close to the midline.
So the geniohyoid ends laterally right here. This is all one muscle right here. Mylohyoid covers this whole area.
So it's going from the whole mandible down to the hyoid bone. The geniohyoid only goes from the chin. So it doesn't attach to the mandible at any other area, just the front.
So we have geniohyoid. The last muscle in this area is this muscle here going from the tongue to the hyoid bone. Okay, so we are attaching here at the hyoid bone and going up to the tongue.
So we call this hyoglossus. A hyoglossus. Hyoid bone up to the tongue. Hyoglossus.
We know glosso is referencing tongue, just like our hypoglossal nerve. Okay, so hyoglossus. Now I would recap this side, but again it is only two additional muscles. So we just have that geniohyoid there. and the hyaluronidase is there.
That's it that we would test you on on the deep side of those superhyoid bones or muscles. Excuse me. All right, so that's superhyoid.
Now this area, the superhyoid region in general, is going to be innervated by a few different nerves. Primarily you're going to see cranial nerves 5 and cranial nerve 7, but there is one muscle in there that's kind of innervated by cranial nerve 12. So for the sake of lab, we are not going to ask you the innervations for any of the suprahyoid muscles. Okay, so again for lab we are not going to ask you the innervations of any of the suprahyoid muscles. That's just these ones here.
Face, which we did first. That's fair game, right? We went over those. But anything that we just went over here, we will not ask you the information of in the lab, okay? In the lab.
Now we can progress down to the infrahyoid muscles. So these are going to be muscles that are on the neck, and they're occurring inferior to that hyoid bone, okay? Inferior to the hyoid bone.
You're going to see, again, we're going to have a lot of, like, the roots that are reflecting the points of attachment for these muscles, okay? And let's not forget, again, this side is going to be more superficial, this side is going to be deeper. And that makes sense because we can already see here there's some vasculature showing. And typically vessels are going to be a little bit deeper in the body.
We don't have a lot of big vessels that sit very close to the surface. And that would be a little dangerous. So let's start with the superficial side here.
We have this muscle here that's going from the sternum. And that's kind of like your breastbone right here. So from the sternum. all the way up to the hyoid bone.
So we're going to call that one sternohyoid. Okay, so from the sternum all the way up to the hyoid bone is sternohyoid. If I look just lateral to the sternohyoid, there's a muscle here that's a bit deceiving because I do see this part here, right? But something that you might not realize is it actually continues under this big muscle.
and comes all the way out here almost into the shoulder. So this muscle collectively going from the shoulder all the way in and up to the hyoid bone is called the omohyoid. The prefix omo actually references the shoulder. So going from the shoulder up to the hyoid bone we have the omohyoid.
Now this is going to be another double belly muscle kind of like how we saw with the digastric. This part of that omohyoid is going to be the superior belly. The superior belly.
That makes sense because it's definitely higher up in the body than the shoulder. So this is the superior belly of the omohyoid. Now to see the inferior belly, all you have to do is kind of lift the model up here. And now you can see that right down there. So that is the inferior belly of that omohyoid heading out towards the shoulder there.
So inferior belly of the omohyoid here is connected to the superior belly, which is right up here. Perfect. Now that big muscle that the omohyoid is going underneath. Okay, so this big muscle here, this is called the sternocleidomastoid. Okay, the sternocleidomastoid.
Again, very, very large muscle. Okay, very superficial. And if we turn it laterally, you can see just how big it is.
So here's that whole muscle, that sternocleidomastoid. If we look at those root words, sterno, we've already seen when we looked at the sternohyoid. So sterno is referencing the sternum, which is one of its attachment points.
Cleido is actually referencing the clavicle. So that's your collarbone here. And then mastoid is referencing the mastoid process on the base of the skull.
Okay, so we have sterno-blido-mastoid. Okay, so that's how we got the name of this really big muscle on the lateral aspect of the neck. Okay, all right, let's go through those one more time. Here, very medial and on the superficial side from the sternum up to the hyoid bone is the sternohyoid muscle. The sternohyoid muscle.
If we move lateral to that, so you see this muscle here, Remember that was part of the omohyoid. Do you remember which belly it is? Is it higher up or lower?
It's going to be higher up. So this is the superior belly of the omohyoid. Omo means shoulder, so the inferior belly has to be down here somewhere.
If we just tilt the model, we can see the inferior belly right down there. Okay, so there's the inferior belly of that omohyoid. And then finally, if we want to see sterno-lido-mastoid in all its glory, probably best from a lateral view. So a view from the side. And we know that that's going from the sternum and the clavicle all the way up to the mastoid process on the base of the skull, giving it its name, sterno-lido-mastoid.
Very large muscle. Okay, that is the superficial side. Let's go to the deep side. So if we're looking at the medial aspect here, we're going to see two muscles.
Now keep in mind, remember most of our superficial muscles had to be cut away so that we can see these. In fact, you can even see a little part of the sternohyoid that's been cut right here. Okay, so that sternal hyoid has been cut away. This line is going to be differentiating from this muscle down here from this muscle up here.
These are two different muscles. All right, so some good things to know before we head into this section. So this muscle is only going from the sternum all the way up to this structure right here.
Okay, this structure is actually part of the larynx. Okay, and we're at the level of the thyroid gland and the thyroid cartilage. So we're going to call this the sternofiroid. The sternofiroid, right? Then from here up, if we're starting at the level of the thyroid now, we're going to call that thyrohyoid because we're going up to the hyoid bone.
Thyrohyoid up to the hyoid bone, right? So just to keep these straight, on the superficial side, we have the sternohyoid. And here we have the sternothyroid, okay? We have the omohyoid superior belly here and the thyrohyoid going from the thyroid all the way up to the hyoid bone, okay? So again, once you get into the practice of using the surrounding structures to name these muscles, these actually become usually some of the easiest ones to name, okay?
You can just see like, okay, well, where does it start? Where is it going to, okay? I'm practicing those out loud a few times because they are a little tricky and just like those levator and depressors around the mouth, they're easy to confuse with one another. Okay, so definitely spend some time with these. Now there is an acronym that will help you in this area, which is TOSS.
T-O-S-S. Okay, the T stands for the thyrohyoid. Thyrohyoid.
The O stands for the omohyoid I'm just going to point to the superior belly for now. So it's the omohyoid. And then we have S and S. One S is the sternohyoid.
The sternohyoid. And the other S is the sternothyroid. So we're stopping at the level of the thyroid. So sternothyroid, sternohyoid. So that's your T-O-S-S.
The TOS muscles, for the sake of this course, we will collectively say that they are innervated by the cervical ansa. Cervical ansa is a fancy way of saying there's a network of nerves that are coming off of the spinal cord at the level of the neck, and they're going to innervate the muscles in this area. The roots for the cervical ansa are C1, C2, and C3. So when those nerves come off of the spinal cord, they kind of create a little network.
and then they give innervation to the surrounding muscles, our TOS muscles. So again, you do not need to understand or know the innervation of the suprahyoid muscles for lab. For the infrahyoid muscles that we just talked about, our TOS muscles right here, these are going to be cervical ansa. So in general, we'll just say cervical ansa here. We have one area, one last area of the neck that we do need to cover.
This is really important. We get a lot of questions on this area, especially when it comes time for the exam, as well as like the homework assignments. OK, so in this area, we're going to have a few muscles called the scalene muscles.
So we have the scalene muscles in this area. All right. The scalene muscles are going to be deep to the sternocleidomastoid, so that's been removed, okay, and they come in a group of three and they're named for where they are in orientation to one another.
Okay, so the three muscles that we're talking about are going to be this one here, this one here, and then this one all the way back here. So again, one, two, three scalene muscles, okay, and you can see they almost kind of make like a triangle, like a scalene triangle. So these three muscles, like I said, are going to be named for where they are in orientation to one another.
This one being the most front facing. So this would be the anterior scalene muscle, the anterior scalene muscle. This one right here would be the middle scalene muscle.
This is the middle scalene muscle here. And then all the way in the back, we have the posterior scalene muscle. So anterior, middle, and posterior scalene muscles. Now you'll notice that between the anterior and the middle scalene muscle, there's a bit of a gap.
There's a space here and there's some structures passing through this area. And this is a really critical point in the neck because what we've done here is we've created space for structures. that start off in the body more medial, so closer to the midline, and we allow them to pass through these muscles, right, without getting pinched or pressed or compressed in any way, and let them get out into the upper limb, okay? So this is a gap in musculature that allows structures to pass through.
That's going to be between the anterior and the middle scalene muscles. So we could say that these two muscles form that gap, we could say they are the borders to that gap, anterior and middle. I would not say that the anterior and the posterior scalene muscles would contribute because it's only the anterior and the middle scalene muscles. Now this gap is referred to as the scalene gap. The scalene gap.
And you should know which muscles contribute to it as well as what structures are passing through it. The first structure here that I want you guys to know is a vessel, and this is actually an artery that moves under the clavicle called the subclavian artery. The subclavian artery is passing through that scalene gap.
It starts off really close to the midline, right, because we're one of the main branches coming kind of from the heart, right, and then we're going to pass through here to get out to the upper limb because we're going to supply the upper limb with oxygenated blood. That is the subclavian artery. And then just above that, all these yellow things right here are representing nerves, because we do have a network of nerves coming off of the spinal cord here known as the brachial plexus. Okay, the brachial plexus.
Brachial is referring to the upper limb. Okay, so what we're going to get from this network of nerves here are a lot of terminal branches or nerves that are going to innervate the muscles of the upper limb. And we'll see this again in block four, let me go over the upper limb. So just to recap this area one more time, we have three primary muscles that we should know.
These are deep to that sternocleidomastoid. They are called the scalene muscles and they are named for where they are in orientation. We have the anterior scalene muscle, the middle scalene muscle, and the posterior scalene muscle. Which of those two or which of those three, which two of those three make up the scalene gap or the borders of the scalene gap? Yeah, the anterior and the middle.
The anterior and middle scaly muscles are contributing to that scaly gap. They don't pass through it. They form the borders of it. Now, what is passing through that space? The brachial plexus, that's these nerves here, and the subclavian artery.
The brachial plexus and the subclavian artery. I think that's really it for this model. Again, make sure that you're giving it enough time to really understand the layers that are present here in these muscles.
Make sure that you're working a lot with this one in the library or in lab or in office hours where we can help you. Okay, remember that you have a superficial versus a deep side of the model. And then as far as secondary material is concerned, you definitely want to make sure you know which muscles are memetic muscles of the face.
Remember our facial expression muscles. Okay. So which muscles are memetic muscles? Which muscles are muscles of mastication?
Okay. So that would be the masseter, the temporalis, which was on this side, and the lateral medial pterygoids. Okay.
You should know your innervations for those muscles. All of the memetic muscles of the face, which is everything basically that we talked about up here on the head, except for our muscles of mastication, those would be the facial nerves. cranial nerve seven, okay? And then for the muscles of mastication, like the masseter here, that was cranial nerve five, the trigeminal nerve, specifically branch three, the mandibular branch, or we can also say the mandibular nerve. We also talked about suprahyoid muscles here, right?
Again, this side is more superficial, this side is a little deeper, okay? You do not need to know the innervations of these for lab, you might get something in lecture. And then now the infrahyoid muscles, okay, so the infrahyoid muscles, which are the ones down here on the neck, right, are toss muscles, right? Our toss muscles, those are going to be that cervical ansa, cervical ansa. That was C1, C2, C3.
And then, of course, we'll want to know about the scaling gap, okay? So what muscles are forming the scaling gap or what muscles are the borders of the scaling gap? That's going to be the anterior.
and the middle scalene muscles. We also might ask you what passes through that scalene gap. It's not going to be a muscle, right?
It's the brachial plexus as well as the subclavian artery. So for secondary material, definitely focus on your innervations. as well as the contents of the scheme gap.