This is a tutorial on the larynx. The larynx is this set of structures here. You've got cartilages, muscles and ligaments which make up the larynx. Below the larynx, it's continuous with the trachea. And above the larynx, you've got the pharynx. You've got the pharynx above and the trachea below.
The function of the larynx is threefold. If the larynx is completely open, it allows breathing. If it's partially open, then it allows distortion of airflow which results in phonation – so talking. And if it's completely closed, it can protect the respiratory system. It’s important in breathing, in phonation and in protection of the respiratory system.
There’s quite a lot to talk about with the larynx. I'm going to do this tutorial in a few parts. I'm going to start with the framework of the larynx. This first tutorial will deal with the cartilages of the larynx and then we'll build on top of it. We’ll add on. We'll add the ligaments on and we'll talk about the membranes and the vocal cords and the muscles and how the larynx functions. The best thing to do is to start off with the framework, the cartilaginous framework.
The larynx is made up of six cartilages. You've got three unpaired cartilages and three paired cartilages. The paired cartilages are smaller and the large, unpaired cartilages are larger. We'll start at the top and work our way down and we'll look at these cartilages in a bit of detail.
Before I talk about the cartilages, it's probably worth mentioning the relationship of the larynx to the hyoid bone. If I just bring in the bones, you can see the hyoid bone here. I've done a tutorial on this bone itself, but you can see this membrane from which the thyroid cartilage is suspended. This is called the thyrohyoid membrane.
And if I just bring in the muscle there, there's a muscle which is quite important as well because this connects from the hyoid bone to the thyroid as well. This is the thyrohyoid muscle. That’s worth remembering because the larynx is suspended from this muscle and this membrane.
If I just get rid of the thyrohyoid membrane, we can take a look at the first cartilage. You can see this cartilage here. This is called the epiglottis. Remember I mentioned one of the functions of the larynx was to protect the respiratory system. The epiglottis is essential because it can close off the opening to the larynx by flapping over and protecting it from any food or debris or anything entering the mouth.
I've just removed the thyroid cartilage. You can see the epiglottis here anteriorly. And if I just remove the mucosa of the larynx and pharynx, you can see that the esophagus is posteriorly and the trachea is anteriorly. The epiglottis can be pulled downwards in front of the opening to the larynx. This prevents any food – so the food will be coming in through the mouth and entering into the orifice and it comes down to the laryngopharynx, but you want it to go posteriorly into the esophagus, not into the respiratory system. The epiglottis can flap backwards over the larynx and protect the airways below.
If we just isolate the epiglottis and the thyroid cartilage, we can have a look at the relationship of these two structures. Firstly, you can see the shape of the epiglottis. It's got this kind of leaf shape and then it's got this stem. You’ve got this stem and leaf shape for the epiglottis and the stem of the epiglottis is connected to the posterior surface of the thyroid by a little ligament called the thyroepiglottic ligament because it connects from the thyroid to the epiglottis.
And also, on the posterior surface of the epiglottis, which isn't every clear on this model, but you've got a little tubercle which sits on the inferior half of the posterior surface of the epiglottis. I've just brought the other structures back in and you can see the ligament attaching the epiglottis to the thyroid cartilage.
Next, we'll just talk about the thyroid cartilage. This is the largest cartilage. It consists of this broad lamina on either side, which meet in the midline and form this prominence, which is known as the laryngeal prominence. If you view this from the lateral aspect, you can see this prominence. This can be seen in males as the Adam's apple. It’s larger in males than in females.
You’ve got this little notch as well where this lamina meet and this is called the superior thyroid notch. It's not very clear on this model, but inferiorly in the midline, you've got a notch called the inferior thyroid notch, but the superior thyroid notch is much more evident.
If we follow the thyroid cartilage around to the back, you can see that it doesn't form a complete ring, it's opened posteriorly. At the top, you've got this bit here which sticks up superiorly. This is called the superior horn. You can see that you've got one on either side. And then at the bottom, you've got the inferior horn.
I've just brought the other structures in and you can see the superior horn here. It actually connects via a thickening of this membrane to the hyoid bone. It connects to the greater horn of the hyoid bone via a ligament here, which is a thickening of the thyrohyoid membrane.
And if we follow the thyroid cartilage down, the inferior horn articulates with the 3rd unpaired cartilage, which is the cricoid cartilage. You've got this articulation with the cricoid cartilage via this inferior horn.
The last thing to mention about the thyroid cartilage is the oblique line. It's not very visible on this model here, but it extends from the base of the superior horn, just a little bit in front of the base of the superior horn down to about midway along the bottom of this lamina.
This oblique line marks the attachment of three muscles. If I just bring in the muscle layer, you can see some muscles have appeared here. The three muscles are the thyrohyoid muscle, so you've got the muscle connecting the hyoid bone to the thyroid cartilage; and then you've got a muscle connecting the thyroid cartilage to the sternum. This is called the sternothyroid muscle; and then you've got a muscle which isn't shown on this model, which sits posteriorly and this is the inferior constrictor muscle. You’ve got three muscles which attach along this oblique line. You can see that the line roughly runs from the base of the superior horn to the middle of the bottom part of this lamina of the thyroid cartilage.
Right at the bottom, we've got this cartilage called the cricoid cartilage. You'll notice that this cartilage forms a complete ring. We're looking at it anteriorly here and you could see it has this narrow arch and at the back, there's this broad lamina. If we rotate the cartilage around to the back, you can see this broad lamina. It’s not clear on this model, but you've got two depressions on either side of the midline where there's this ridge. These depressions serve as the attachment for the posterior cricoarytenoid muscles. There are muscles which attach on the cricoid, which we'll talk about later. But remember that we saw the inferior horn of the thyroid cartilage articulating with the cricoid cartilage.
I just brought these structures back in. You've got a facet on the cricoid cartilage laterally which articulates with the inferior horn of the thyroid cartilage. This is a synovial joint, so it has a joint capsule and ligaments.
If we rotate the model around posteriorly, we can see that there are two other cartilages which sit on top of the cricoid. These two cartilages sitting superiorly on the cricoid are called the arytenoid cartilages.
We’ve talked about the three unpaired cartilages. We've got the epiglottis, the thyroid and the cricoid cartilage. And now we've got the paired cartilages. You’ve got the arytenoid cartilages sitting on top of the cricoid. And on top of the arytenoid cartilages, you can see these horn-shaped cartilages. These are called the corniculate cartilages. They get the name from the Latin 'corny' which means 'horn'. You can see they're like these horn shapes.
Let’s take a look at the arytenoid cartilages. They've got this triangular shape. They've got a base which articulates with the cricoid cartilage and the apex articulates with the horn-shaped corniculate cartilage.
You can see that the medial surfaces of the arytenoid cartilage face each other. And then you've got this anterolateral surface which has two depressions where muscles can attach and ligaments can attach. And you can see this obvious process pointing out here. These are called the vocal process, which serves as the point of attachment for the vocal ligament, which is shown on this model here.
And then you've got this process sticking out posteriorly. This kind of sticks out posteriorly and laterally. I'll just rotate it around to the back and you can see this process which is called the muscular process. It serves as the attachment for the posterior and lateral cricoarytenoid muscles.
The arytenoid cartilages are quite interesting, but we'll come on and talk about the intricacies and muscle attachments of the arytenoid cartilages in another tutorial. For this part, just learn about the vocal process, the muscular process, the base which articulates with the cricoid cartilage, the apex which articulates with the corniculate cartilage and it's got this anterolateral surface which has two depressions where muscles attach and ligaments attach. You’ve got your vocalis muscle and vestibular ligament, which attach on this anterolateral surface here.
The final pair of cartilages which I haven't mentioned yet is the cuneiform cartilages. They're not shown on this model because they're actually suspended in the quadrangular membrane. They can't be visualised in this model, but they sit a little bit anteriorly to the corniculate cartilages. They're suspended in a membrane. I'll show you them in the next tutorial.