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