Anatomy and Function of Mastication Muscles

One of my favorite facts about the muscles of mastication or chewing is that whenever you are chewing, you can actually feel two of the muscles. So take your fingers and put up right here at your temple. And while you chew, you can feel a muscle kind of bulging there. That's your temporalis muscle. And then also put your hand right here. The muscle you can feel bulging right there is your masseter muscle. Both of those are muscles of mastication, are muscles involved in the process of chewing. But in this video, we're going to learn the four primary muscles of mastication. We're going to learn the origin, insertion, and then the movements of each of those. We'll learn the innervations of those, like the nerves that control them, as well as a little bit about the blood supply for those muscles. And then we'll talk about the accessory muscles of mastication just a little bit. Those are going to be the muscles in the neck. They're going to help to like lower the jaw whenever you're about to take a bite. And through it all, we're going to use these 3D models from anatomy.app, which is the app that I'm actually using to learn all of this. So it comes highly recommended. So link in the description more about anatomy.app later in the video. And let's jump to the app and get started. Let's start with a quick overview of the four primary muscles of mastication. So I've got a skull pulled up here and it's just going to show the muscles that are involved in mastication. The first one is the temporalis. And that's going to be this muscle that kind of spans this whole temporal area of your skull right here. It's going to connect from that temporal region down to part of the mandible. You can kind of see it down in there. And whenever that contracts, it's going to lift the mandible up. Same thing with the masseter muscle. So here we've got the masseter muscle. I just think masseter and mastication, those kind of sound similar. So let's try to remember those go together. So you have the temporalis and then the masseter. The masseter is going to connect from the zygomatic arch here. down to the mandible and that's going to pull up on the mandible whenever we are biting down. So temporalis masseter and then on the posterior side we can see the two pterygoid muscles. So we've got the medial pterygoid right here and then a little bit deeper in there from this view we've got the lateral pterygoid and if we kind of zoom in here a little bit we can see that this is the medial pterygoid so it kind of goes a little bit further towards the midline of the skull and the lateral pterygoid It has an origin out here, so a little bit more lateral in its origin than the medial pterygoid. And those pterygoid muscles are going to do things like protruding the mandible, like if you stick your jaw out like this. And they also help to elevate and depress the mandible as well, but we'll get more into those actions later on. So those are the four primary muscles of mastication. We've got the masseter, the temporalis, and then on the posterior side, we can see the medial pterygoid and the lateral pterygoid. Now let's take each of those one by one and go into their origins and insertions and actions. But before we do that, we need to take a look at the mandible. Here's a picture of just the mandible, and the mandible is really the only bone of the skull that's moving a lot. Most of the other bones of our skull are all fused together. There's not really much movement happening, but we've got a lot of movement here. And that's why the insertion points for all four of these muscles are going to be on the mandible. So we're going to learn a few parts of the mandible so we can better talk about those insertions of these four muscles. So I'm going to toggle on some labels onto our model here. And when I do, you're going to see a lot of words pop up. We're just interested on the ones on the right side right here. There's kind of two regions to the mandible. We've got the body of the mandible, which is going to be all of this right here, the part that kind of sticks out in the front and your chin. And then we've got the ramus of the mandible. So we've got the right ramus and the left ramus of the mandible and a couple other parts around that ramus that we need to know. One is the angle of the mandible. So on your jaw, it's this kind of back. Pointy part Ridge part right there where it kind of makes an angle We've got two processes as well that we need to know one of those is the coronoid process It's kind of sticking up kind of spike like right here. I think of it like like it's a thing on a crown And coronoid has kind of the same root, corona, coronoid. I think of a crown for that. And we also have the condylar process. And the condylar process, this is actually where the mandible is going to articulate with the temporal bone, forming the temporomandibular joint. So a lot of people have heard of the temporomandibular or TMJ joint because it's a common place where people have joint pain in their jaw. And we call this the condyloid process because that joint is a condyloid type synovial joint. So again, we've got the body of the mandible, the ramus, of the mandible, the angle, here we have the coronoid process, and then the condylar process of the mandible. Now let's jump back to our muscles and we'll start with the temporalis muscle. So I've got the temporalis muscle here in blue, and you can see a lot of fibers of the temporalis muscle. There's really going to be kind of three regions of fibers we're going to talk about. We've got the anterior fibers right here, the mid fibers right here, and the posterior fibers right there. And they're going to have slightly different actions depending on which fibers are contracting. So first let's talk about the origin and the insertion of these fibers. So the origin is going to be the temporal fossa. So this whole region of the temporal area right here, but it's not just the temporal area. bone. In fact, it's several skull bones that we need to look at here. We've got the frontal bone right here. So part of the origin is going to be on the frontal bone. We've got the parietal bone, one of the parietal bones. Remember, we've got two parietal bones, the right and left parietal. So if we go back to here, we've got the parietal bone. We've got the temporal bone, which is all this down here, and it kind of extends up into there. So the temporal bone, it's going to have an origin there. And then there's a little section of bone, the sphenoid bone, which is right under there. And so all four of those bones, frontal, parietal, temporal, and sphenoid, those all make up this part of the temporal fossa where the origin of the temporalis muscle is. So when this muscle is contracting, this will be the stationary origin part. And then the insertion is going to be on the coronoid process of the mandible. So one of those structures that we just learned about. So whenever this contracts, this is going to pull on that coronary process to pull up the mandible or to elevate the mandible, like whenever you're taking a bite. For elevating the mandible, it's primarily going to be the anterior fibers and the mid fibers that are pulling directly up on it to elevate the mandible. If you have contraction of the posterior fibers though, since these are back here and they're running kind of horizontal almost, those are actually going to be pulling the mandible back or posteriorly. So if you take your jaw and you kind of pull it in like this, you're using some of those posterior fibers of the temporalis muscle to do that. So quick recap, temporalis muscle, the origin is the temporal fossa. We've got the insertion, which is the coronoid process of the mandible, and that's going to cause elevation as well as retraction of the mandible. Up next, we have the masseter muscle. Let's talk about the origin first. The origin is going to be this whole zygomatic arch right in there. It's going to be the inferior border of the zygomatic arch, and that really is going to include two different bones. Here's the zygomatic bone of the skull. Here's the temporal bone of the skull, but this part that sticks out right there, that's part of the temporal bone. It's a little bit confusing here, but this is going to be the zygomatic process of the temporal bone. And right here we have the temporal process of the zygomatic bone. But together, all of that is going to make the zygomatic arch and the inferior border of the zygomatic arch. That's where the origin of the masseter is located. You can feel your zygomatic bone. It's this bone right here kind of jutting out. So it's that arch right there. That's where the masseter is connected. Now for the insertion of the masseter, it's going to all be on the posterior outer part of the mandible. So this section right back in here, it's going to include kind of three main areas. One is going to be the angle of the mandible right in here. It's also going to include the ramus of the mandible right in there. And then there's one part of it that's kind of hard to see, but it's going to be connected to the coronoid process of the mandible as well. And the primary action of this is going to be to elevate the mandible, like whenever you're taking a bite during chewing. And so when you contract those anterior fibers, that's going to actually jut the jaw forward just a little bit. So it's not the main muscle that's causing protrusion of the mandible, but it does contribute a little bit because of the angle of these anterior fibers. So a quick recap of the master muscle. We've got the zygomatic arch, the inferior border of that zygomatic arch as the origin. We've got the angle and the ramus. and the condyloid process of the mandible as the insertion. And when the masseter contracts, the primary motion is to elevate the mandible, like when you're taking a bite, but it also works a little bit to protrude the mandible. So up next, we're gonna look at the pterygoid muscles. But before we do that, we need to learn a few parts of the skull. And also I'd like to take you behind the scenes a little bit on this app that I'm using. So here I've got pulled up the masseter muscle. I've got all this information about the masseter muscle, more diagrams and all this. And this is actually the stuff that I'm using to learn all of these different muscles and origins and insertions and everything. So I've really enjoyed this process. It's kind of like being on an anatomy-based Wikipedia with really amazing 3D diagrams that I can learn from. If you want to know more, check out the link in the description as well as a coupon code for 10% off if you're interested in learning the same way that I am. So jumping back to the skull, here's some bones that we need to know. We've got the mandible we've been talking about. We have the maxilla, which is the part above your mouth. We've got the zygomatic bone that we've talked about a little bit. If I move this over, we have the temporal bone, and there's that zygomatic arch of the temporal bone. There's the sphenoid bone that I mentioned earlier. And what we want to know, though, is the bones if we look kind of underneath like this. So let me zoom in here a little bit. And I just mentioned the sphenoid bone right here, but this is just a small section of the sphenoid bone. The sphenoid bone is all of this dark green right in here. And if I move right here, you can see there's a couple of ridges that extend down. These are called the pterygoid plates of the sphenoid bone. That's going to be important for the pterygoid muscles. We've got the lateral pterygoid plate right here. We've got the medial pterygoid plate right here. You would think that the lateral pterygoid will connect to the lateral plate and the medial to the medial. It's just not actually how it is. The lateral pterygoid is going to have an origin on the lateral side of the lateral pterygoid. And the medial pterygoid is going to have an origin on the medial side. of the lateral pterygoid plate. But the main thing to know right now is this is the pterygoid plate of the sphenoid bone which is going to be important for us. But also I want to point out, if you look where this ridge kind of ends, there's a couple other bones involved right in there. This is actually part of the maxilla and the purple right there. So maxilla, and I rotate it around, it's still part of the maxilla. And then this in the yellow right here is the palatine bone. And so in this section right in there, they all kind of come together. And so there's going to be parts of the pterygoid muscles that are going to have an origin on the palatine bone as well as maxilla, although mostly it's going to be on the pterygoid ridge of the sphenoid bone. So now that we know some parts. of the skull, let's take a look at the medial pterygoid first. So let me zoom in here a little bit. We've got the medial pterygoid here in blue, and it actually has two parts to it, or two heads to the muscle. We've got the deep head right here and the superficial head in yellow. And so I rotate this around a little bit. You can see this one's a little bit deeper. This one's a little bit more superficial of those two parts, but this is the medial pterygoid. And then the deep head right here is actually going to have an origin on part of the palatine bone. and the maxilla. So you see that origin right in there. It's technically not the sphenoid bone, but the palatine bone and the maxilla. Now the insertion of the pterygoids is going to be on the inner part of the angle and ramus of the mandible. So kind of similar to the masseter on this side, but now we're looking on the inside part of it. Now let's think about the actions that are going to happen whenever this muscle contracts. First of all, if you think about this contracting, that's going to be elevating this part of the mandible. So it's going to work to elevate the mandible, like when you're taking a bite. Similar to the master, these will be synergist with each other for that particular movement. It's also going to work to protrude the mandible. So if I think about this, when these contract, that's going to be moving the mandible this direction, moving it forward a little bit. So it's also going to help to protrude the mandible. So elevate the mandible and protrude the mandible. Now those movements I just described are called bilateral contractions, meaning that both of those pterygoid muscles, the left and the right medial pterygoid, will be contracting at the same time causing those movements. We can also do unilateral contractions, which is where one of the sides, like the medial pterygoid on the right side, contracts, but not the left pterygoid. And that's going to cause side-to-side movements like this. And these are going to be to the opposite side of the muscle that's contracting. So if I contract the right pterygoid muscle, that's going to move my jaw to the left. And if I contract my left pterygoid muscles, that's going to move my jaw to the right. So that's the medial pterygoid. Let's do a quick recap. It has an origin, which is going to be on the medial side of the lateral pterygoid plate of the sphenoid bone, as well as, in this case for the superficial head, the maxilla and the palatine bone. It's going to have insertions on the inner part of the mandible, specifically the angle and the ramus, the inner parts of those on the mandible. And when it contracts, it's going to do several including elevating the mandible, protruding the mandible. And if you do unilateral contractions, it can move the mandible side to side. on the opposite side of whichever medial pterygoid muscle is contracting. Finally we have the fourth muscle of mastication which is the lateral pterygoid. So let me zoom in a little bit here. The lateral pterygoids are a little bit harder to see from this perspective. They're kind of back behind the medial pterygoid right there. So we've got the lateral pterygoid and we've got two heads to that as well. We've got a superior head and an inferior head of the lateral pterygoid. Now the lateral pterygoids are going to have a similar origin as the medial pterygoid. But instead of being on the medial side of the lateral pterygoid plate of the sphenoid bone, they're going to be on the lateral side of the lateral pterygoid plate of the sphenoid bone. And the inferior head is going to have a part of its origin as well on the maxilla and the palatine bone. Now the insertion of the lateral pterygoid is going to be the most different insertion that we've had yet because it's not going to be on this kind of like lower or inferior part of the mandible. It's actually going to have an insertion way at the top right here on the condylar process of the mandible. It's getting way up in there in that TMJ joint. In fact, not only does it connect to the condylar joint, it's going to connect to part of the TMJ joint itself. In particular, the joint capsule and the articular disc of the TMJ joint. So let's think about the movements that'll happen whenever we're contracting that muscle then. So if you think about it from this perspective here. And when these contract, that's going to be pulling the mandible forward or protruding the mandible, like when we're sticking our chin forward. It's not, however, going to elevate the mandible. So far, all three muscles that we've looked at, the temporalis, masseter, and medial pterygoid, have all worked to elevate the mandible, like when we're taking a bite. But the lateral pterygoid is not going to do that because of where its insertion is. Instead of its insertion being down here and pulling up, its insertion is up here on the condylar process. So it's going to be pulling more kind of downward. So this is going to work to depress or lower the mandible. When contracting unilaterally, again, meaning just one side or the other is contracting, it'll work as a synergist with the mandible. the medial pterygoid to cause those side-to-side movements. So like if I move my jaw to the left, that's going to be my right medial and lateral pterygoids contracting to move that jaw to the left. And the same thing if I do it on the left side, if I contract the medial. lateral pterygoids on the left side that I move my jaw to the right. So quick recap of the lateral pterygoid. It's going to have an origin on the sphenoid bone, the lateral side of the lateral pterygoid plate of the sphenoid bone, as well as part of the maxilla and palatine bone. It's going to have an insertion on the condylar process and as well as the joint capsule and articular disc of the TMJ joint. And when it contracts, it'll work to protrude the mandible forward. as well as depress or lower the mandible and when you contract it unilaterally it'll work as a synergist with the medial pterygoids to cause side to side movements up next let's take a look at the innervation or the nerves that connect to all of these muscles of mastication so how we how do we control those what nerve do we use so all four of those muscles are controlled by a cranial nerve Specifically, it's going to be controlled by the trigeminal nerve. That's cranial nerve 5. We use the Roman numeral V for that. So this is the trigeminal nerve. It's the largest of the cranial nerves. And in this diagram, it's cut off right there. So let's jump to another diagram to see where this nerve continues on. All right, so this is all the trigeminal nerve. Let's zoom in a little bit on this. So the trigeminal nerve is coming out of the brain stem right there. And it's going to have three branches to it. We've got the ophthalmic branch of the trigeminal nerve. We've got the maxillary branch of the trigeminal nerve, and then we have the mandibular branch of the trigeminal nerve. And all of these muscles are going to be controlled by the mandibular branch of the trigeminal nerve. So this branch right here is cut off in this diagram. So let's jump to another diagram to see where it continues on to. So this diagram is showing all of the parts of the mandibular branch. So I can zoom in on this. This mandibular branch does a lot. Everything here is part of that mandibular branch. It's going to control like a lot of stuff in the jaw. A lot of this is going to be sensory neurons as well. But if you jump in right here, there's this particular branch coming down right there, and that's going to branch off into a bunch of different parts. And those are going to go to all four of these muscles that we've been talking about, the temporalis, masseter, and medial and lateral pterygoid muscles. So this right here is the anterior branch of the mandibular part of the trigeminal nerve, which is cranial nerve five. And this is what's going to innervate with all of these muscles that we've been talking about. It'll have branches that come down here to the pterygoids, as well as it's going to have branches that come around here, up into the temporalis, as well as into the masseter. Finally, let's take a look at the blood supply for the muscles of mastication. All right, so here we have a model that's showing all of the blood supply or all the arteries that are going to the face and the neck and everything. So we're going to zoom in on this, and there's a couple arteries in particular that we need to know. So if I come down here, we've got the carotid artery right there. And that's gonna branch off into the external carotid as well as the internal carotid arteries. We're interested in the external carotid artery branch right here. And if I come up here, there's gonna be three main arteries we're gonna need to know for this video. One is gonna be the facial artery. So this one right here, the facial artery, it actually kinda comes up, does a U-turn, comes down around the mandible, and then comes way up over here throughout the face. And so that is the facial artery, which is a branch of the external carotid artery. Then we have the maxillary artery, which is this artery right here. That's another branch off of that external carotid, the maxillary artery. It's going to come up here into the maxillary region. And the final branch we need to know here is the superficial temporal artery. Superficial temporal artery, we'll branch off and go into this kind of temporal region right there. So let's start with the temporalis muscle real quick. The temporalis, which the muscle itself we know is in this region right here, but it's actually going to be two parts, the maxillary artery. It's going to have a branch that's going to come off of it and come up here into the temporalis. And then the superficial temporal artery. it's going to have this middle branch and that's going to go to the temporalis muscle it's not going to be this branch or this branch the anterior and the posterior it's going to be the middle branch that's going up into that temporalis muscle right there next we have the masseter so let's come back down here we've got the maxillary artery right there and then one of the branches coming off of the maxillary artery is going to be the masseteric artery which is going to go down to the masseter and then last the blood supply to the pterygoids is going to come partly from the facial artery right here so there's going to be some branches coming up off that's going to go to the pterygoids branching off of this loop of the facial artery as well as there's going to be some pterygoid branches of the maxillary artery so some of these branches coming off the maxillary artery are going to go down to the pterygoid muscles as well but again all of the blood supply for these muscles is coming mainly from the maxillary artery as well as the facial artery as well as for the temporalis is coming from the superficial temporal artery as All right, finally, last thing I want to talk about in this, they're going to be the accessory muscles of mastication. I'm not going to go through all the... Origins and insertions and everything, but I'm going to give you kind of a basic overview of what these accessory muscles do. So the first one to talk about here is the buccinator muscle. That's going to be this muscle right here. It's in your cheek right in there, and that's going to help to kind of push food. back into the mouth whenever you're chewing. So it's not involved in like the motion of your jaw of chewing really, but it's involved of kind of the pushing of the food and keeping it where it needs to be whenever you're chewing. And then underneath that, we're gonna have all of these muscles that make up parts of the neck right here. And so we're gonna have suprahyoid muscles. That's gonna be all of the muscles right here. And we have infra or below hyoid muscles, infrahyoid muscles right here. The hyoid bone is this kind of half circle shaped bone right there and it's going to be just directly superior to the thyroid cartilage so if you can find your thyroid cartilage right here go slightly above that that's where your hyoid bone is going to be and what all these muscles are going to really assist in is going to be depressing the mandible so here's kind of how they do that we've got the mylohyoid muscle right here as well as on the posterior side of it we've got the geniohyoid muscle right there And then we've got the digastric muscle. There's actually two bellies to the digastric muscle. This is maybe the coolest muscle in the neck. It has two bellies to it, two parts to it. There's a tendon between them. And then there's this fibrous loop right here off the hyoid that it threads through. And so it kind of connects the anterior part of the mandible with this part of the temporal bone. And it's gonna connect it to the hyoid bone by threading through a loop. That's just super cool, I think. So this anterior belly of the digastric muscle, as well as the mylohyoid, as well as the geniohyoid right there, those are all three going to contract to depress the mandible. And that kind of makes sense. It's going to be stabilized by the hyoid bone. When those contract, it's going to pull the jaw down. The problem though, is the hyoid bone can move a little bit. And so by contracting this, it's only going to lower the jaw if we've stabilized the hyoid bone. And that's what the rest of these muscles, the infrahyoid muscles, are going to be doing. They're going to be stabilizing the hyoid so that when these suprahyoid muscles contract, you can actually pull down on the jaw. So those infrahyoid muscles include the sternohyoid right there, connecting the hyoid to the sternum. It's going to include the sternothyroid, not to be confused with the sternohyoid. Sternohyoid again, hyoid to the sternum. Sternothyroid is only going to go up to the thyroid. cartilage right there and then down to the sternum we can see down underneath there and then we've got the omohyoid which is going to connect the hyoid bone actually to the scapula right in there That's the omohyoid. So those are the infrahyoid muscles that are going to be stabilizing the hyoid bone. So when the suprahyoid muscles contract, we can depress the mandible. Thanks for watching. Hopefully you learned a ton about the muscles of mastication. We've got the temporalis, the masseter, the medial, and the lateral pterygoids. Can you name all the origins and insertions and innervations and blood supply and all of that and the actions of all of those muscles? If you're trying to learn all that stuff, again, anatomy.app, I think, is the way to go. Check out my link in the description there. It's an affiliate link. If you sign up for a subscription to anatomy.app, it helps out the channel a little bit. I also have a 10% off coupon code. So check out that coupon code in the description. Also, I have a link to a table that summarizes a lot of this information from the video. So check that out as well. And I've got some other resources that can help you learn anatomy and physiology. So it's all in the description. I'm not going to talk any more about that. Again, thanks for watching. And I'll catch you in the next video. See ya.

And then also put your hand right here. The muscle you can feel bulging right there is your masseter muscle. Both of those are muscles of mastication, are muscles involved in the process of chewing.

But in this video, we're going to learn the four primary muscles of mastication. We're going to learn the origin, insertion, and then the movements of each of those. We'll learn the innervations of those, like the nerves that control them, as well as a little bit about the blood supply for those muscles.

And then we'll talk about the accessory muscles of mastication just a little bit. Those are going to be the muscles in the neck. They're going to help to like lower the jaw whenever you're about to take a bite.

And through it all, we're going to use these 3D models from anatomy.app, which is the app that I'm actually using to learn all of this. So it comes highly recommended. So link in the description more about anatomy.app later in the video. And let's jump to the app and get started.

Let's start with a quick overview of the four primary muscles of mastication. So I've got a skull pulled up here and it's just going to show the muscles that are involved in mastication. The first one is the temporalis. And that's going to be this muscle that kind of spans this whole temporal area of your skull right here.

It's going to connect from that temporal region down to part of the mandible. You can kind of see it down in there. And whenever that contracts, it's going to lift the mandible up. Same thing with the masseter muscle.

So here we've got the masseter muscle. I just think masseter and mastication, those kind of sound similar. So let's try to remember those go together.

So you have the temporalis and then the masseter. The masseter is going to connect from the zygomatic arch here. down to the mandible and that's going to pull up on the mandible whenever we are biting down.

So temporalis masseter and then on the posterior side we can see the two pterygoid muscles. So we've got the medial pterygoid right here and then a little bit deeper in there from this view we've got the lateral pterygoid and if we kind of zoom in here a little bit we can see that this is the medial pterygoid so it kind of goes a little bit further towards the midline of the skull and the lateral pterygoid It has an origin out here, so a little bit more lateral in its origin than the medial pterygoid. And those pterygoid muscles are going to do things like protruding the mandible, like if you stick your jaw out like this.

And they also help to elevate and depress the mandible as well, but we'll get more into those actions later on. So those are the four primary muscles of mastication. We've got the masseter, the temporalis, and then on the posterior side, we can see the medial pterygoid and the lateral pterygoid.

Now let's take each of those one by one and go into their origins and insertions and actions. But before we do that, we need to take a look at the mandible. Here's a picture of just the mandible, and the mandible is really the only bone of the skull that's moving a lot. Most of the other bones of our skull are all fused together.

There's not really much movement happening, but we've got a lot of movement here. And that's why the insertion points for all four of these muscles are going to be on the mandible. So we're going to learn a few parts of the mandible so we can better talk about those insertions of these four muscles.

So I'm going to toggle on some labels onto our model here. And when I do, you're going to see a lot of words pop up. We're just interested on the ones on the right side right here. There's kind of two regions to the mandible.

We've got the body of the mandible, which is going to be all of this right here, the part that kind of sticks out in the front and your chin. And then we've got the ramus of the mandible. So we've got the right ramus and the left ramus of the mandible and a couple other parts around that ramus that we need to know. One is the angle of the mandible.

So on your jaw, it's this kind of back. Pointy part Ridge part right there where it kind of makes an angle We've got two processes as well that we need to know one of those is the coronoid process It's kind of sticking up kind of spike like right here. I think of it like like it's a thing on a crown And coronoid has kind of the same root, corona, coronoid.

I think of a crown for that. And we also have the condylar process. And the condylar process, this is actually where the mandible is going to articulate with the temporal bone, forming the temporomandibular joint. So a lot of people have heard of the temporomandibular or TMJ joint because it's a common place where people have joint pain in their jaw. And we call this the condyloid process because that joint is a condyloid type synovial joint.

So again, we've got the body of the mandible, the ramus, of the mandible, the angle, here we have the coronoid process, and then the condylar process of the mandible. Now let's jump back to our muscles and we'll start with the temporalis muscle. So I've got the temporalis muscle here in blue, and you can see a lot of fibers of the temporalis muscle. There's really going to be kind of three regions of fibers we're going to talk about.

We've got the anterior fibers right here, the mid fibers right here, and the posterior fibers right there. And they're going to have slightly different actions depending on which fibers are contracting. So first let's talk about the origin and the insertion of these fibers.

So the origin is going to be the temporal fossa. So this whole region of the temporal area right here, but it's not just the temporal area. bone. In fact, it's several skull bones that we need to look at here.

We've got the frontal bone right here. So part of the origin is going to be on the frontal bone. We've got the parietal bone, one of the parietal bones. Remember, we've got two parietal bones, the right and left parietal. So if we go back to here, we've got the parietal bone.

We've got the temporal bone, which is all this down here, and it kind of extends up into there. So the temporal bone, it's going to have an origin there. And then there's a little section of bone, the sphenoid bone, which is right under there. And so all four of those bones, frontal, parietal, temporal, and sphenoid, those all make up this part of the temporal fossa where the origin of the temporalis muscle is. So when this muscle is contracting, this will be the stationary origin part.

And then the insertion is going to be on the coronoid process of the mandible. So one of those structures that we just learned about. So whenever this contracts, this is going to pull on that coronary process to pull up the mandible or to elevate the mandible, like whenever you're taking a bite.

For elevating the mandible, it's primarily going to be the anterior fibers and the mid fibers that are pulling directly up on it to elevate the mandible. If you have contraction of the posterior fibers though, since these are back here and they're running kind of horizontal almost, those are actually going to be pulling the mandible back or posteriorly. So if you take your jaw and you kind of pull it in like this, you're using some of those posterior fibers of the temporalis muscle to do that.

So quick recap, temporalis muscle, the origin is the temporal fossa. We've got the insertion, which is the coronoid process of the mandible, and that's going to cause elevation as well as retraction of the mandible. Up next, we have the masseter muscle. Let's talk about the origin first. The origin is going to be this whole zygomatic arch right in there.

It's going to be the inferior border of the zygomatic arch, and that really is going to include two different bones. Here's the zygomatic bone of the skull. Here's the temporal bone of the skull, but this part that sticks out right there, that's part of the temporal bone. It's a little bit confusing here, but this is going to be the zygomatic process of the temporal bone. And right here we have the temporal process of the zygomatic bone.

But together, all of that is going to make the zygomatic arch and the inferior border of the zygomatic arch. That's where the origin of the masseter is located. You can feel your zygomatic bone. It's this bone right here kind of jutting out.

So it's that arch right there. That's where the masseter is connected. Now for the insertion of the masseter, it's going to all be on the posterior outer part of the mandible.

So this section right back in here, it's going to include kind of three main areas. One is going to be the angle of the mandible right in here. It's also going to include the ramus of the mandible right in there. And then there's one part of it that's kind of hard to see, but it's going to be connected to the coronoid process of the mandible as well. And the primary action of this is going to be to elevate the mandible, like whenever you're taking a bite during chewing.

And so when you contract those anterior fibers, that's going to actually jut the jaw forward just a little bit. So it's not the main muscle that's causing protrusion of the mandible, but it does contribute a little bit because of the angle of these anterior fibers. So a quick recap of the master muscle.

We've got the zygomatic arch, the inferior border of that zygomatic arch as the origin. We've got the angle and the ramus. and the condyloid process of the mandible as the insertion.

And when the masseter contracts, the primary motion is to elevate the mandible, like when you're taking a bite, but it also works a little bit to protrude the mandible. So up next, we're gonna look at the pterygoid muscles. But before we do that, we need to learn a few parts of the skull.

And also I'd like to take you behind the scenes a little bit on this app that I'm using. So here I've got pulled up the masseter muscle. I've got all this information about the masseter muscle, more diagrams and all this.

And this is actually the stuff that I'm using to learn all of these different muscles and origins and insertions and everything. So I've really enjoyed this process. It's kind of like being on an anatomy-based Wikipedia with really amazing 3D diagrams that I can learn from. If you want to know more, check out the link in the description as well as a coupon code for 10% off if you're interested in learning the same way that I am. So jumping back to the skull, here's some bones that we need to know.

We've got the mandible we've been talking about. We have the maxilla, which is the part above your mouth. We've got the zygomatic bone that we've talked about a little bit. If I move this over, we have the temporal bone, and there's that zygomatic arch of the temporal bone.

There's the sphenoid bone that I mentioned earlier. And what we want to know, though, is the bones if we look kind of underneath like this. So let me zoom in here a little bit.

And I just mentioned the sphenoid bone right here, but this is just a small section of the sphenoid bone. The sphenoid bone is all of this dark green right in here. And if I move right here, you can see there's a couple of ridges that extend down.

These are called the pterygoid plates of the sphenoid bone. That's going to be important for the pterygoid muscles. We've got the lateral pterygoid plate right here. We've got the medial pterygoid plate right here.

You would think that the lateral pterygoid will connect to the lateral plate and the medial to the medial. It's just not actually how it is. The lateral pterygoid is going to have an origin on the lateral side of the lateral pterygoid. And the medial pterygoid is going to have an origin on the medial side. of the lateral pterygoid plate.

But the main thing to know right now is this is the pterygoid plate of the sphenoid bone which is going to be important for us. But also I want to point out, if you look where this ridge kind of ends, there's a couple other bones involved right in there. This is actually part of the maxilla and the purple right there.

So maxilla, and I rotate it around, it's still part of the maxilla. And then this in the yellow right here is the palatine bone. And so in this section right in there, they all kind of come together. And so there's going to be parts of the pterygoid muscles that are going to have an origin on the palatine bone as well as maxilla, although mostly it's going to be on the pterygoid ridge of the sphenoid bone.

So now that we know some parts. of the skull, let's take a look at the medial pterygoid first. So let me zoom in here a little bit.

We've got the medial pterygoid here in blue, and it actually has two parts to it, or two heads to the muscle. We've got the deep head right here and the superficial head in yellow. And so I rotate this around a little bit.

You can see this one's a little bit deeper. This one's a little bit more superficial of those two parts, but this is the medial pterygoid. And then the deep head right here is actually going to have an origin on part of the palatine bone. and the maxilla.

So you see that origin right in there. It's technically not the sphenoid bone, but the palatine bone and the maxilla. Now the insertion of the pterygoids is going to be on the inner part of the angle and ramus of the mandible. So kind of similar to the masseter on this side, but now we're looking on the inside part of it. Now let's think about the actions that are going to happen whenever this muscle contracts.

First of all, if you think about this contracting, that's going to be elevating this part of the mandible. So it's going to work to elevate the mandible, like when you're taking a bite. Similar to the master, these will be synergist with each other for that particular movement.

It's also going to work to protrude the mandible. So if I think about this, when these contract, that's going to be moving the mandible this direction, moving it forward a little bit. So it's also going to help to protrude the mandible.

So elevate the mandible and protrude the mandible. Now those movements I just described are called bilateral contractions, meaning that both of those pterygoid muscles, the left and the right medial pterygoid, will be contracting at the same time causing those movements. We can also do unilateral contractions, which is where one of the sides, like the medial pterygoid on the right side, contracts, but not the left pterygoid.

And that's going to cause side-to-side movements like this. And these are going to be to the opposite side of the muscle that's contracting. So if I contract the right pterygoid muscle, that's going to move my jaw to the left. And if I contract my left pterygoid muscles, that's going to move my jaw to the right. So that's the medial pterygoid.

Let's do a quick recap. It has an origin, which is going to be on the medial side of the lateral pterygoid plate of the sphenoid bone, as well as, in this case for the superficial head, the maxilla and the palatine bone. It's going to have insertions on the inner part of the mandible, specifically the angle and the ramus, the inner parts of those on the mandible. And when it contracts, it's going to do several including elevating the mandible, protruding the mandible. And if you do unilateral contractions, it can move the mandible side to side.

on the opposite side of whichever medial pterygoid muscle is contracting. Finally we have the fourth muscle of mastication which is the lateral pterygoid. So let me zoom in a little bit here. The lateral pterygoids are a little bit harder to see from this perspective.

They're kind of back behind the medial pterygoid right there. So we've got the lateral pterygoid and we've got two heads to that as well. We've got a superior head and an inferior head of the lateral pterygoid. Now the lateral pterygoids are going to have a similar origin as the medial pterygoid.

But instead of being on the medial side of the lateral pterygoid plate of the sphenoid bone, they're going to be on the lateral side of the lateral pterygoid plate of the sphenoid bone. And the inferior head is going to have a part of its origin as well on the maxilla and the palatine bone. Now the insertion of the lateral pterygoid is going to be the most different insertion that we've had yet because it's not going to be on this kind of like lower or inferior part of the mandible.

It's actually going to have an insertion way at the top right here on the condylar process of the mandible. It's getting way up in there in that TMJ joint. In fact, not only does it connect to the condylar joint, it's going to connect to part of the TMJ joint itself.

In particular, the joint capsule and the articular disc of the TMJ joint. So let's think about the movements that'll happen whenever we're contracting that muscle then. So if you think about it from this perspective here. And when these contract, that's going to be pulling the mandible forward or protruding the mandible, like when we're sticking our chin forward.

It's not, however, going to elevate the mandible. So far, all three muscles that we've looked at, the temporalis, masseter, and medial pterygoid, have all worked to elevate the mandible, like when we're taking a bite. But the lateral pterygoid is not going to do that because of where its insertion is. Instead of its insertion being down here and pulling up, its insertion is up here on the condylar process. So it's going to be pulling more kind of downward.

So this is going to work to depress or lower the mandible. When contracting unilaterally, again, meaning just one side or the other is contracting, it'll work as a synergist with the mandible. the medial pterygoid to cause those side-to-side movements. So like if I move my jaw to the left, that's going to be my right medial and lateral pterygoids contracting to move that jaw to the left.

And the same thing if I do it on the left side, if I contract the medial. lateral pterygoids on the left side that I move my jaw to the right. So quick recap of the lateral pterygoid. It's going to have an origin on the sphenoid bone, the lateral side of the lateral pterygoid plate of the sphenoid bone, as well as part of the maxilla and palatine bone. It's going to have an insertion on the condylar process and as well as the joint capsule and articular disc of the TMJ joint.

And when it contracts, it'll work to protrude the mandible forward. as well as depress or lower the mandible and when you contract it unilaterally it'll work as a synergist with the medial pterygoids to cause side to side movements up next let's take a look at the innervation or the nerves that connect to all of these muscles of mastication so how we how do we control those what nerve do we use so all four of those muscles are controlled by a cranial nerve Specifically, it's going to be controlled by the trigeminal nerve. That's cranial nerve 5. We use the Roman numeral V for that. So this is the trigeminal nerve.

It's the largest of the cranial nerves. And in this diagram, it's cut off right there. So let's jump to another diagram to see where this nerve continues on.

All right, so this is all the trigeminal nerve. Let's zoom in a little bit on this. So the trigeminal nerve is coming out of the brain stem right there.

And it's going to have three branches to it. We've got the ophthalmic branch of the trigeminal nerve. We've got the maxillary branch of the trigeminal nerve, and then we have the mandibular branch of the trigeminal nerve. And all of these muscles are going to be controlled by the mandibular branch of the trigeminal nerve. So this branch right here is cut off in this diagram.

So let's jump to another diagram to see where it continues on to. So this diagram is showing all of the parts of the mandibular branch. So I can zoom in on this. This mandibular branch does a lot. Everything here is part of that mandibular branch.

It's going to control like a lot of stuff in the jaw. A lot of this is going to be sensory neurons as well. But if you jump in right here, there's this particular branch coming down right there, and that's going to branch off into a bunch of different parts.

And those are going to go to all four of these muscles that we've been talking about, the temporalis, masseter, and medial and lateral pterygoid muscles. So this right here is the anterior branch of the mandibular part of the trigeminal nerve, which is cranial nerve five. And this is what's going to innervate with all of these muscles that we've been talking about. It'll have branches that come down here to the pterygoids, as well as it's going to have branches that come around here, up into the temporalis, as well as into the masseter. Finally, let's take a look at the blood supply for the muscles of mastication.

All right, so here we have a model that's showing all of the blood supply or all the arteries that are going to the face and the neck and everything. So we're going to zoom in on this, and there's a couple arteries in particular that we need to know. So if I come down here, we've got the carotid artery right there.

And that's gonna branch off into the external carotid as well as the internal carotid arteries. We're interested in the external carotid artery branch right here. And if I come up here, there's gonna be three main arteries we're gonna need to know for this video. One is gonna be the facial artery. So this one right here, the facial artery, it actually kinda comes up, does a U-turn, comes down around the mandible, and then comes way up over here throughout the face.

And so that is the facial artery, which is a branch of the external carotid artery. Then we have the maxillary artery, which is this artery right here. That's another branch off of that external carotid, the maxillary artery. It's going to come up here into the maxillary region.

And the final branch we need to know here is the superficial temporal artery. Superficial temporal artery, we'll branch off and go into this kind of temporal region right there. So let's start with the temporalis muscle real quick.

The temporalis, which the muscle itself we know is in this region right here, but it's actually going to be two parts, the maxillary artery. It's going to have a branch that's going to come off of it and come up here into the temporalis. And then the superficial temporal artery. it's going to have this middle branch and that's going to go to the temporalis muscle it's not going to be this branch or this branch the anterior and the posterior it's going to be the middle branch that's going up into that temporalis muscle right there next we have the masseter so let's come back down here we've got the maxillary artery right there and then one of the branches coming off of the maxillary artery is going to be the masseteric artery which is going to go down to the masseter and then last the blood supply to the pterygoids is going to come partly from the facial artery right here so there's going to be some branches coming up off that's going to go to the pterygoids branching off of this loop of the facial artery as well as there's going to be some pterygoid branches of the maxillary artery so some of these branches coming off the maxillary artery are going to go down to the pterygoid muscles as well but again all of the blood supply for these muscles is coming mainly from the maxillary artery as well as the facial artery as well as for the temporalis is coming from the superficial temporal artery as All right, finally, last thing I want to talk about in this, they're going to be the accessory muscles of mastication. I'm not going to go through all the...

Origins and insertions and everything, but I'm going to give you kind of a basic overview of what these accessory muscles do. So the first one to talk about here is the buccinator muscle. That's going to be this muscle right here.

It's in your cheek right in there, and that's going to help to kind of push food. back into the mouth whenever you're chewing. So it's not involved in like the motion of your jaw of chewing really, but it's involved of kind of the pushing of the food and keeping it where it needs to be whenever you're chewing. And then underneath that, we're gonna have all of these muscles that make up parts of the neck right here.

And so we're gonna have suprahyoid muscles. That's gonna be all of the muscles right here. And we have infra or below hyoid muscles, infrahyoid muscles right here. The hyoid bone is this kind of half circle shaped bone right there and it's going to be just directly superior to the thyroid cartilage so if you can find your thyroid cartilage right here go slightly above that that's where your hyoid bone is going to be and what all these muscles are going to really assist in is going to be depressing the mandible so here's kind of how they do that we've got the mylohyoid muscle right here as well as on the posterior side of it we've got the geniohyoid muscle right there And then we've got the digastric muscle. There's actually two bellies to the digastric muscle.

This is maybe the coolest muscle in the neck. It has two bellies to it, two parts to it. There's a tendon between them. And then there's this fibrous loop right here off the hyoid that it threads through.

And so it kind of connects the anterior part of the mandible with this part of the temporal bone. And it's gonna connect it to the hyoid bone by threading through a loop. That's just super cool, I think. So this anterior belly of the digastric muscle, as well as the mylohyoid, as well as the geniohyoid right there, those are all three going to contract to depress the mandible.

And that kind of makes sense. It's going to be stabilized by the hyoid bone. When those contract, it's going to pull the jaw down.

The problem though, is the hyoid bone can move a little bit. And so by contracting this, it's only going to lower the jaw if we've stabilized the hyoid bone. And that's what the rest of these muscles, the infrahyoid muscles, are going to be doing.

They're going to be stabilizing the hyoid so that when these suprahyoid muscles contract, you can actually pull down on the jaw. So those infrahyoid muscles include the sternohyoid right there, connecting the hyoid to the sternum. It's going to include the sternothyroid, not to be confused with the sternohyoid. Sternohyoid again, hyoid to the sternum.

Sternothyroid is only going to go up to the thyroid. cartilage right there and then down to the sternum we can see down underneath there and then we've got the omohyoid which is going to connect the hyoid bone actually to the scapula right in there That's the omohyoid. So those are the infrahyoid muscles that are going to be stabilizing the hyoid bone.

So when the suprahyoid muscles contract, we can depress the mandible. Thanks for watching. Hopefully you learned a ton about the muscles of mastication.

We've got the temporalis, the masseter, the medial, and the lateral pterygoids. Can you name all the origins and insertions and innervations and blood supply and all of that and the actions of all of those muscles? If you're trying to learn all that stuff, again, anatomy.app, I think, is the way to go.

Check out my link in the description there. It's an affiliate link. If you sign up for a subscription to anatomy.app, it helps out the channel a little bit. I also have a 10% off coupon code. So check out that coupon code in the description.

Also, I have a link to a table that summarizes a lot of this information from the video. So check that out as well. And I've got some other resources that can help you learn anatomy and physiology.

So it's all in the description. I'm not going to talk any more about that. Again, thanks for watching. And I'll catch you in the next video.

See ya.

Transcript for:Anatomy and Function of Mastication Muscles

Transcript for:
Anatomy and Function of Mastication Muscles