So we've looked at muscles which attach to the cricoid to the thyroid and produced downward
and forward movement which helps to tighten the vocal cords and produce higher pitched
sounds.
And then we looked at the posterior and lateral cricoarytenoid muscles which attach to the
cricoid to the arytenoid cartilages.
And now we're going to look at the muscles which connect the arytenoid cartilages together.
So we've got interarytenoid muscles because they connect, they run between both cartilages,
the arytenoid cartilages.
So you've got two muscles which run between the arytenoid cartilages.
We've got a transverse arytenoid muscle and we've got an oblique arytenoid muscle.
So we're looking at a posterior view of the cricoid with the arytenoid cartilage sitting
on top.
We've got the transverse arytenoid muscle running from the posterior lateral surface
of one arytenoid cartilage to the posterior and lateral surface of the other arytenoid
cartilage.
So you can see that if this muscle contracts, it's going to bring the arytenoid cartilages
closer together.
It adducts the arytenoid cartilages.
And again, it's innervated by the recurrent laryngeal nerve.
And then we've got the oblique arytenoid muscles.
These originate posteriorly on the surface of the muscular process.
So now we've seen two muscles attaching to this muscular process already, the posterior
and lateral cricoarytenoid.
And now we're seeing a third.
This is the oblique arytenoid muscle which originates from the posterior surface of the
muscular process.
And then it runs obliquely (which gives its name) and attaches on the opposite cartilage.
So it attaches at the back of the apex of the other arytenoid cartilage.
So you've got two of these.
So the other one obviously has the same origin and insertion.
So it runs from the posterior surface of the muscular process of the arytenoid cartilage
and inserts on the apex of the other arytenoid cartilage.
So if we just rotate this model around, the oblique arytenoid muscle is quite interesting
because some sources say that the muscle continues past.
So when it reaches the apex of the arytenoid cartilage, it continues around and forms this
muscle which attaches to the epiglottis.
So this is referred to as the aryepiglottic muscle and it's sometimes considered part
of the oblique arytenoid muscle.
So it's considered a continuation of the oblique arytenoid muscle.
So if you imagine this oblique arytenoid muscle attaching from the muscular process to the
apex of the arytenoid cartilage opposite and then you've got this aryepiglottic muscle
which might be a continuation of this muscle, but it attaches from the arytenoid cartilage
and it runs up in the aryepiglottic fold to attach to the epiglottis, so you've got this
aryepiglottic muscle.
So you can see if this aryepiglottic muscle were to contract, it would close the laryngeal
inlet -- bring the epiglottis down and close the laryngeal inlet.
So whether or not the aryepiglottic muscle is considered a part of the oblique arytenoid
or not, just remember that there is a muscle that there is a muscle attaching from the
arytenoid cartilage to the epiglottis and it can close the laryngeal inlet.
So the interarytenoid muscle, the transverse arytenoid and the oblique arytenoid and the
aryepiglottic parts or the aryepiglottic muscle are innervated by the recurrent laryngeal
nerve.
So the last muscle we're going to talk about is the thyroarytenoid muscle.
The best way to show you this is through a cross section.
So I'm going to rotate the thyroid cartilage around laterally and I'm going to slice it
through the middle.
So we're now looking at a slice of the larynx.
I've cut it through the midline, so you can see it like that.
So I'll just rotate it around laterally and we'll be able to look at the inside of this
cartilage now.
So remember between the cricoid cartilage and the thyroid cartilage, you've got this
cricothyroid membrane.
The thyroarytenoid muscle attaches from the thyroid cartilage to the arytenoid cartilage.
It originates around this area here.
So it attaches to the thyroid angle and a little bit to the cricothyroid membrane below.
And then it attaches to the anterolateral surface of the arytenoid cartilage.
So it's quite a broad muscle.
You've also got some fibers given off from the thyroarytenoid muscle onto the epiglottis.
So you've got fibers coming up on the lateral surface of the epiglottis.
This is referred to as the thyroepiglottic muscle or the thyroepiglottic part of the
thyroarytenoid muscle.
So remember, you've also got the aryepiglottic muscle which is a part of the oblique arytenoid
muscle.
So the thyroarytenoid muscle is often thought of as two parts.
So you've got the vocalis muscle and you've got the thyroarytenoid part.
It depends on the source you look at, but different sources tell you different thing.
In this tutorial, we're going to look at the vocalis muscle as a separate muscle and the
thyroarytenoid as a separate muscle.
So the thyroarytenoid muscle originates on the thyroid angle and below, it has attachments
to the cricothyroid ligament and then it inserts onto the anterolateral surface of the arytenoid
cartilage.
And then it gives off these fibers which attach to the lateral surface of the epiglottis.
So this is the thyroepiglottic muscle.
And I'll just draw on this muscle here which connects the arytenoid to the epiglottis.
And this is the aryepiglottic muscle.
So I'm just showing you this diagram here which shows a nice illustration of what I've
shown you.
So we're looking at the same kind of section with the thyroid cut through the midline.
You've got these fibers going up to the epiglottis, the thyroepiglottic muscle.
You've got the broad thyroarytenoid muscle and you've got the aryepiglottic muscle here.
So the thyroarytenoid muscle has two parts.
So we're going to look at the vocalis muscle, which is considered a part of the thyroarytenoid
muscle.
So just coming back to the 3D model, what we're going to do is we're going to rotate
it around anteriorly and then we're going to look superiorly down at the larynx.
So from this view, you can see the attachment of the vocalis muscle.
The vocalis muscle runs lateral to the vocal ligament.
You can see the vocal ligament here.
The vocalis muscle, it originates on the lateral surface of the vocal process and it inserts
along the vocal ligament.
So it attaches along the vocal ligament and it also attaches at the thyroid angle.
The function of the thyroarytenoid muscle and the vocalis muscle is to adjust the tension
in the vocal cords.
So remember we looked at the cricothyroid muscle which could stretch the vocal ligament
and thereby produce higher pitched sounds, the thyroarytenoid muscle, when it contracts,
it brings the arytenoid cartilage closer to the thyroid cartilage.
This results in a slackening or a loosening of the vocal ligaments.
This produces lower pitched sounds.
So the vocalis muscle which we're looking at separately has the function of making small
adjustments which result in changing the pitch and the quality of the voice and phonation
and the sounds produced, whereas the broad sheets of muscles, the rest of the thyroarytenoid
muscle is responsible for larger adjustments of the tension in the vocal cords.
So I just thought I'd show you this diagram as well just to show you the relationship
of the thyroarytenoid muscle to the other structures in the larynx.
So we're looking at a coronal section here.
You can see the epiglottis here, the aryepiglottic folds dropping downwards from the lateral
aspect of the epiglottis.
And then you've got the vestibular folds folding around the vestibular ligament.
And then you've got the laryngeal ventricle and you've got the vocal fold folding around
the vocal ligament.
So I'll just draw on the vocal fold here.
This is the most medial structure I'm going to show you.
And then we're just inside that.
We've got the cricothyroid ligament.
So that connects from the -- this is the cricoid cartilage down here.
So attaching from the cricoid cartilage, you've got the cricoid ligament.
And remember the upper border of the cricoid ligament forms the vocal ligament where the
vocal folds fold around.
And then just lateral to that, you've got the thyroarytenoid muscle, so you can see
that here.
So that should give you some idea of the kind of relationship of the muscles to the folds
and the membranes and ligaments and that kind of thing.
So that's the thyroarytenoid muscle.
So we've covered all the muscle of the larynx now.
it's useful just to think in terms of how they affect the opening and closing of the
rima glottidis, how they affect the tension of the vocal cords and these functions affect
phonation and protection of the respiratory tract.