This tutorial is on the mucosa of the larynx. We're going to look at how the mucosa folds to form the true and false vocal cords.
We're looking anteriorly at the lungs here. I'm just going to rotate the model around and we're going to look superiorly down. We’ve got the tongue here anteriorly and now we're just going to zoom in and look into the larynx.
You’ve got mucosa which lines the epiglottis and the structures of the larynx. You can see this pink stuff here. This is representing the mucosa. It's not entirely accurately in this model, so I'm going to talk you through it to explain it.
Connecting to the lateral aspect of the epiglottis, we've got mucosa which hangs down. I'll come on to that in a moment. First, we'll talk about the mucosa which reflects off the anterior surface of the tongue, the anterior surface of the epiglottis onto the back of the tongue, the base of the tongue.
We've got mucosa which attaches the tongue to the epiglottis. In the midline, we've got some mucosa which reflects back and attaches onto the tongue from the epiglottis and laterally, on other side, we've got reflections of mucosa which attach to the tongue like so. I'm just drawing this on very broadly.
And in between these reflections, you've got these little depressions. These are called vallecula. The reflection in the midline is called the median glossoepiglottic fold. And laterally, you've got two lateral glossoepiglottic folds. You’ve got the glossoepiglottic fold on either side and you've got one in the midline, which reflect from the epiglottis onto the tongue. You've got two depressions on either side of the midline which are called vallecula.
I've just switched over to this diagram here and it shows what I just showed you in diagrammatic form. You’ve got the epiglottis here. You've got the base of the tongue here. You've got these reflections of the mucosa, so the median glossoepiglottic fold and you've got the lateral glossoepiglotic fold on either side with the vallecula on either side of the median glossoepiglottic fold.
Coming back to the 3D model, what we're looking at is the epiglottis here. It isn't shown on this model here, but the mucosa actually attaches laterally to the epiglottis. It kind of drapes off the epiglottis. It hangs off laterally. It hangs down and connects to the arytenoid cartilages and forms the entrance to the larynx. It forms the laryngeal inlet which I've described to you.
Remember, we're looking at this superior view and I'll just orientate you quickly. I've just removed the mucosa and you can see the arytenoid cartilages sitting on top of the cricoid cartilage. You can see the little corniculate cartilages sitting on top of the arytenoid cartilages. We’re looking straight down the larynx. You can see the trachea, the rings of the trachea here.
I've just brought back the mucosa. You can see posteriorly the little slit, which is the opening of the esophagus behind.
Remember I told you that the mucosa shown here isn't entirely accurate. It actually attaches to the lateral margins of the epiglottis and it connects to the arytenoid. Remember, the position of the arytenoid cartilages is around here. The mucosa hangs off the sides of the epiglottis and attaches to the arytenoid cartilages and it forms this fold called the aryepiglottic fold.
Suspended within this fold of mucosa, you've got a little cartilage called the cuneiform cartilage. You’ve got a little round bump on either side called the cuneiform cartilage. And then it envelops the arytenoid cartilage which sits around here. And then the mucosa joins posteriorly like this.
When you're looking at the superior view like you might do with a laryngoscope, you've got the epiglottis anteriorly and then laterally, you've got these aryepiglottic folds which connect from the sides of the epiglottis to the arytenoid cartilage. And then you've got little bumps here which you can now recognize as the cuneiform cartilages suspended in the aryepiglottic fold. You've got the arytenoid cartilages which you know about.
What we're looking at here is the laryngeal inlet. This is the entrance to the larynx. Anteriorly, we've got this mucosa lining the superior aspect of the epiglottis. And then laterally, we've got these aryepiglottic folds which I've just told you about. And so you've got these two tubercles which mark the cartilages which you know about. The first one is the cuneiform cartilage and the second one is a tubercle marking the position of the corniculate cartilage sitting on top of the arytenoid cartilage. And then you've got these posterior border formed between a fold of mucosa which sits between the two arytenoid cartilages.
When looking at the superior view, you don’t really get a sense of the oblique angle of this laryngeal inlet. You know that the arytenoid cartilage is lower than the top of the epiglottis. This inlet is not at the same level. It's oblique. This laryngeal inlet can be closed by the epiglottis moving down and closing off the entrance to the larynx.
I've just switched over to this diagram and this shows what I've just show you in diagrammatic form. You've got the epiglottis here anteriorly. And then you've got these folds of mucosa coming off the sides of the epiglottis and they connect to the arytenoid cartilage. They contain the cuneiform and the corniculate cartilage. And then there's this connection posteriorly between the arytenoid cartilages. This is the laryngeal inlet that we're looking at.
The mucosa forms folds over the vestibular ligaments first to form the vestibular fold. This is this fold here. And then you've got the vocal fold where the mucosa folds over the vocal ligament. The vestibular fold here, which folds over the vestibular ligament is referred to as the false vocal cord and the vocal cord which folds over the vocal ligament is called the true vocal cord.
I've just switched to the 3D model. You can see that we're now looking at a cross-section of the laryngeal structures. I'm just going to rotate the model around and I'll talk you through the mucosa from a different angle.
You’ve got the epiglottis here seen dissected from the middle view. We've got the arytenoid cartilage sitting posteriorly. We've got the vocal ligament extending from the vocal process to the thyroid angle inside the thyroid and we've got the broad lamina of the thyroid cartilage shown here.
The aryepiglottic fold drapes down over the epiglottis from the sides of the epiglottis onto the arytenoid cartilage. It hangs off the sides of the epiglottis which I'm drawing on here.
You can see from the view I showed you earlier, the laryngeal inlet is at an oblique angle. in this diagram here, it's actually shown vertical, but if you imagine the epiglottis pulled backwards so it's more upright – so I've just drawn a more upright epiglottis in blue – so the aryepiglottic fold would hang off kind of like this onto the arytenoid cartilage and it's more at an oblique angle.
Just coming back to this drawing, we've got the aryepiglottic fold hanging off the sides of the epiglottis here. Remember, connecting from the superior depression of the anterolateral surface of the arytenoid cartilage, we've got the thickening of the quadrangular membrane, which forms the vestibular ligament.
The quadrangular membrane sits just outside the mucosa. The mucosa lines this quadrangular membrane and it actually envelops this superior margin only. We’ve got this vestibular ligament here and the aryepiglottic fold, this fold of mucosa folds underneath this ligament. It comes and folds underneath the ligament. And then it goes out laterally like this. And then it curves back in and it folds under the vocal ligament.
the best way to show you how these folds form the vocal and vestibular folds is to take a cross-section right down through here, a cranial section and show you this in a diagram. We're looking here at a coronal section of the larynx. You’ve got the epiglottis at the top and you've got the folds of mucosa coming off here.
What we're looking at here is the mucosa coming down, descending into the larynx and it folds outwards, laterally underneath the vestibular ligament. And then, it comes back out and it folds over the vocal ligament. You’ve got this trough formed by the folds of mucosa and this is called the laryngeal ventricle. And then you can see how the mucosa continues downwards and continues with the trachea below.
This first fold is called the vestibular fold. This is the false vocal cord. The second fold is the vocal fold and this is the true vocal cord. The true vocal cord can be seen as a white structure and the vestibular folds can be seen as a more pinkish structure.
These folds divide up the larynx into three major compartments. You’ve got an upper compartment, a middle compartment and a lower compartment. The upper compartment is above the vestibular fold and below the laryngeal inlet. It’s this area here. This is called the vestibule.
Middle compartment lies between the vocal folds and the vestibular folds, so it's this middle region here. It's a very thin little space.
And the inferior compartment of the laryngeal cavity is the infraglottic space. This bottom chamber is the infraglottic space. It extends from below the vocal folds to the opening of the larynx into the trachea. The larynx ends at the bottom of the cricoid cartilage and it becomes continuous with the trachea here. This is the infraglottic compartment.
You’ve got the supraglottic compartment, the vestibule, which lies above the vestibular folds) and the laryngeal inlet. And then you've got the middle chamber, which lies between the vocal folds and the vestibular folds. And then you've got the infraglottic compartment which lies between the vocal folds and the opening of the larynx into the trachea, so the bottom of the cricoid cartilage where it becomes continuous with the trachea.
Where the mucosa bulges out here between the vocal and vestibular folds, you've got this space, this sort of trough. This space between these folds is called the laryngeal ventricle. You can see this dotted line extending backwards and upwards, this is the laryngeal sacule. This sacule has glands which produce secretions which lubricate the larynx.
You’ve got the laryngeal sacule and the laryngeal ventricle. The sacule has glands which secrete mucous secretions to lubricate the vocal folds.
This diagram here shows a sagittal section. We can see the epiglottis here with the aryepiglottic fold and the mucosa hanging down. And then we've got the vestibular ligament, so the mucosa folds underneath the vestibular ligament. This back space here shows the laryngeal ventricle. And then, it folds back over the vocal ligament, so you've got the vocal fold.
Just to show you from another angle. Just coming back to this superior view, I just want to point out that the space between the vocal folds is called the rima glottidis and the space between the vestibular folds is referred to as the rima vestibuli.
That’s the mucosal folds and lining of the larynx. I hope that's given you a better understanding of what the vocal folds are and how the mucosa is draped over these laryngeal structures and how the laryngeal cavity and ventricle and sacule are formed.