In this tutorial, we're going to talk about the membranes and the ligaments of the larynx. And then we're going to look at how the mucosa folds over the ligaments to form the vocal cords.
We’re looking here anteriorly at the larynx. You can see the trachea below and the hyoid bone at the top.
The ligaments of the larynx can be separated into intrinsic and extrinsic ligaments. The extrinsic ligaments are ligaments which connect the larynx to other structures, so ligaments which connect the larynx to the hyoid bone and ligaments which connect the larynx to the trachea below. The intrinsic ligaments are the ligaments which connect the individual cartilages of the larynx together. We'll first take a look at the extrinsic ligaments.
These are quite simple. The larynx attach to the hyoid above. You can see this big membrane here connecting the thyroid cartilage to the hyoid bone. This is called the thyrohyoid membrane. There are two things to mention about this membrane. Anteriorly, it's thickened. What I'm showing you here is the thyrohyoid ligament is thickened to form the median thyrohyoid ligament.
And laterally, if you remember from the last tutorial where the membrane attaches from the superior horn of the thyroid cartilage to the hyoid bone, it is thickened laterally to form the lateral thyrohyoid ligament.
You can also see this little hole in the membrane. This is for the superior laryngeal vessels and nerve to enter.
The thyrohyoid ligament connects the thyroid to the hyoid. And now we'll look at the ligament connecting the epiglottis to the hyoid bone. this is called the hyoepiglottic ligament.
Finally, there's a ligament connecting the lowest cartilage, the cricoid cartilage to the trachea. This ligament is called the cricotracheal ligament.
Next we've got the intrinsic ligaments. These ligaments are important in forming the cavity of the larynx itself and is structurally important ligaments and they're important in the function of the larynx. They're a little bit more complicated, so I'll try and explain them as best I can.
Just like I mentioned in the thickenings of the thyrohyoid membranes, you've got thickenings of these other two membranes called the cricothyroid membrane and the quadrangular membrane. These thickenings form ligaments which are important because combined with the folds of mucosa, they form the vocal cords. We'll just take a look at these now.
The first ligament I'm going to talk about is the cricothyroid ligament. The cricothyroid ligament is also referred to as the cricothyroid membrane. We're looking anteriorly at the larynx here and the cricothyroid membrane attaches to the arch of the cricoid. You can see this narrow arch here of the cricoid. It attaches onto the ring. You'll be able to see it like this if you're looking at it anteriorly. The model doesn't show this ligament, but if you're looking at it anteriorly, the ligament sits here. It actually attaches inside the thyroid cartilage. We'll take a cross-section of the thyroid and look at its attachment inside.
If I just rotate the model around, from a lateral view, you'll be able to see the cricothyroid ligament attaching like this.
And now what I've done here is I've taken a cross section of the larynx. It's basically a median-sagittal section. We've chopped right through the middle of these structures and we're looking at it from the inside. Just to make sure you're orientated, this is the lateral aspect of the thyroid, so you can see the broad lamina. This is the beginning of the narrow arch of the cricoid cartilage anteriorly. This little space here would contain the cricothyroid membrane or ligament.
We’re switching to the inside view. You saw how the ligament would attach if you're looking at an anterior view, but on the inside, the ligament attaches like this. It attaches to the inside of the thyroid. And at the top, this is the important point, the ligament has a free margin. This free margin is thickened to form the vocal ligament.
Inside the thyroid, it attaches anteriorly and it also attaches to the vocal process of the arytenoid cartilage. there is a free upper margin of the cricothyroid membrane and this upper margin is thickened to form the vocal ligament which attaches from the vocal process of the arytenoid cartilage to inside the thyroid.
If we just zoom into this model, you can see the arytenoid cartilage here. The bit sticking out is called the vocal process and attaching to it is this ligament. The membrane is not shown here, but the thickened upper margin is. this is the vocal ligament.
I've put back the thyroid cartilage in full. If we rotate to superior view, you can see the arytenoid cartilages posteriorly and there, the vocal ligament attaching from the vocal process to just inside the thyroid cartilage.
Two last points to mention with regard to the cricothyroid membrane. In the midline, it's actually thickened to form the median cricothyroid ligament. And then the lateral parts of the cricothyroid ligament or membrane are actually referred to as the conus elasticus. These lie close under the mucous membrane. They are what I showed you. They extend from the superior border of the cricoid to the inferior margin of the vocal ligaments, which is the upper margin of the cricothyroid membrane. You've got the conus elasticus laterally and you've got the median cricothyroid ligament which is this thickening anteriorly in the midline.
The next membrane we've got is the quadrangular membrane. If I just rotate the model around, I can try and describe the quadrangular membrane to you. I just got rid of the thyroid cartilage. We're going to take a closer look at what we've got here. The quadrangular membrane attaches to the lateral surface of the epiglottis and it attaches to the arytenoid cartilage and the corniculate cartilage about it. And also, it attaches to the thyroid cartilage above the point where the vocal ligament attaches to the thyroid cartilage.
I'm just going to draw on there the quadrangular membrane. It's got this attachment to the corniculate and arytenoid cartilage. And then it's got this free lower margin which attaches above the point of where the vocal ligament attaches to the inside of the thyroid cartilage. It attaches from the lateral aspect of the epiglottis. And then it attaches to the arytenoid and the corniculate cartilage. And then it has this free lower margin which attaches to the inside of the thyroid cartilage.
This free lower margin as you might guess is thickened. This thickening forms a ligament called the vestibular ligament. This ligament attaches to the superior depression on the anterolateral surface of the arytenoid cartilage. It attaches inside the thyroid cartilage above the point of attachment where the vocal ligament attaches.
We’ve now seen two ligaments formed by thickenings of the free margins of two membranes. The cricothyroid membrane attaches along the arch of the cricoid and to the vocal process of the arytenoid cartilage and it has this free margin which attaches from the vocal process to the inside of the thyroid cartilage. You've got a thickened upper border of this cricothyroid membrane forming the vocal ligament and you've got this thickened lower border of the quadrangular membrane attaching from the superior depression of the anterolateral surface of the arytenoid cartilage to the inside of the thyroid cartilage.
We’ve got the vocal ligament below and the vestibular ligament above, both of which attach to the arytenoid and to the inside surface of the thyroid cartilage.
I've just stuck two pins. This pin here, you can see it's stuck into the superior depression of the arytenoid cartilage. The other pin is inserted into the inside of the thyroid cartilage about the thyroid angle. The vestibular ligament runs between these two pins.
The significance of the ligaments that I've described to you, the vestibular ligament and the vocal ligament is that they form the vocal cords.
I've just removed the thyroid cartilage again and I'll just show you what I mean. The vestibular ligament is above and to the side of the vocal ligament. The mucosa of the larynx folds around these ligaments to form vocal folds and vestibular folds. These folds are the vocal cords. The fold of mucosa that wraps around the vestibular ligament is called the vestibular fold and this is the false vocal cord. The fold of mucosa which wraps around the vocal ligament is called the vocal fold and this is the true vocal cord.
You’ve got this mucous membrane which hangs down from the side of the epiglottis and it folds. Remember the vestibular ligament is above and to the side of the vocal ligament, so it folds inwards onto this ligament. And then it comes back and then it folds again under the vocal ligament. And then it continues this down.
This first fold is the vestibular fold and it's called the false vocal cord and this second fold forms the true vocal cords and is called the vocal fold.
That was the ligaments of the larynx. We've got the extrinsic ligaments which attach the larynx to other structures – so the trachea and the hyoid bone. They're quite straightforward. And then you've got the intrinsic ligaments which attach the cartilages of the larynx to each other. You've got the quadrangular membrane and you've got the cricothyroid membrane. The important thing to remember is the free upper border of the cricothyroid membrane forms the vocal ligament and the free lower border of the quadrangular membrane forms the vestibular ligament.
You've got the folds of mucosa which folds around these ligaments to form the false and true vocal cords. You've got the vestibular folds which folds around the vestibular ligament, which forms the false vocal cord. And then you've got the vocal folds which folds around the vocal ligament to form the true vocal cord.
That’s a little bit about the vocal cord's membranes and ligaments of the larynx.