hi let's talk about the intrinsic laryngeal muscles
intrinsic laryngeal muscles are muscles which connect elements of the laryngo skeleton
to itself so for instance they may run between the cricoid cartilage and the arytenoid cartilage
or between the arytenoid cartilage and the thyroid cartilage these
are not muscles which connect elements of the laryngoskeleton
to skeletal elements outside of the larynx those would be extrinsic laryngeal muscles so
to begin let's discuss the cricothyroid muscle the cricothyroid muscles as their names would suggest
connect the cricoid cartilage to the thyroid cartilage so we have a pair of them right
here this is an anterior view of the neck we can see a little bit of the cricoid cartilage there
we could see a very nicely defined thyroid cartilage there there is our laryngeal prominence
here is that median cricothyroid membrane and when these cricothyroid muscles contract
look at the directions of these grains they're going to tip the thyroid cartilage
anteriorly and inferiorly when this happens that places extra tension
on the vocal ligaments that's going to increase pitch the cricothyroid muscles are unique among
all of the intrinsic laryngeal muscles and that they are the only intrinsic laryngeal muscles
which are innervated by a nerve other than the recurrent laryngeal nerve and that would be the
external branch of the superior laryngeal nerve which is a branch of the vagus nerve
so let's turn our attention to the posterior aspect of the larynx
so i'll just circle the larynx for us here so that we can see it
so the laryngopharynx has been incised and reflected away to review reveal the the larynx
and nestled here let's erase this so we can get a little bit better of a view nestled here
um and this would be posterior to the aretenoid cartilages so there's one arytenoid cartilage and
there's the other arytenoid cartilage but let's erase that we can see muscles that crisscross like so
and run transversely like so together these are known as the arytenoid muscles
and there are both oblique arytenoid muscles
and transverse arytenoid muscles both of these are innervated by the recurrent laryngeal nerve
these are going to adduct adduct the arytenoids so they're going to pull
them towards the midline in a in a gliding fashion and when that happens that's going to narrow the
rima glottidis so if i were to kind of draw an example here so these would be the vocal folds
this would be the sort of the posterior cricoid lamina and you'd have the
arytenoid cartilages sitting there and there what happens when we
slide these arytenoid cartilages together is that the vocal folds slide together and
this narrows the rima glottidis so this would bring it into closer approximation for phonation
there are also cricoarytenoid muscles uh so cricoarytenoid muscles are going to
attach the cricoid cartilage to the arytenoid cartilages
sticking with our our posterior view here we can see two of these muscles one there
and the other there and let's draw in the grain so that we can appreciate what's going on here
so these crico these posterior crico arytenoid muscles so let's label this this would be the
posterior are going to run from sort of the posterior medial aspect of the cricoid cartilage
up to the muscular processes of the aretenoid cartilages and when that happens when these
muscles contract as a result of stimulus from the recurrent laryngeal muscles those
arytenoid cartilages pivot so let's look at what happens when they pivot so there are our vocal
folds here are those arytenoid cartilages and i'll just draw that posterior aspect of the uh
of the cricoid laminae there so there's our muscular process there are the
vocal processes of the arytenoid cartilage when the muscles contract they're going to oops
they're going to pivot the arytenoid cartilages that way when that happens that's going to
pivot the vocal folds out of the way because these all turn in the same direction
and as a result we expand the rima glottidis and so we're we're making this area more patent
we open it for maximum air exchange so turning our attention here uh to the left so this would be a
left lateral view of the larynx so the thyroid cartilage has been cut midline and this one has
been reflected slightly away here's our cricoid cartilage here right here we can see our posterior
cricoarytenoid muscle we also have a lateral cricoarytenoid muscle here
and what happens with these lateral crico-arytenoid muscles so we'll draw this again like so
there's the muscular process again when the lateral crico-arytenoid muscles contract they pull
the muscular processes this way and so we have a pivoting inwards so these lateral cricoarytenoid
muscles are going to adduct the vocal folds and narrow the rima glottidis
finally we have the thyroarytenoid muscles the thyroaretenoid muscles are going to attach the
thyroid cartilage to the arytenoid cartilages so the thyroid cartilage we can see has been cut
there for the purposes of reflection the cricoid cartilage and the posterior lamina
there has been cut and reflected out so that we can see inward and the mucosa has
been stripped away so that we can see some of the elements such as the vocal ligament here
and there and we can see these thyroarytenoid muscles
the thyroarytenoid muscles when they contract they're going to pull the arytenoid cartilages
anteromedially towards the thyroid cartilage and that's going to decrease tension on the
vocal ligaments so that's going to decrease pitch and these are innervated like nearly all but one
of the other intrinsic laryngeal muscles by the recurrent laryngeal nerves now
there is some debate uh there's inconsistency in in how these muscles are named some consider
the fibers of the thyroid retinoid muscles that are immediately adjacent to the vocal ligaments
to be either specialized elements of thyroid retinoid or their own separate muscles so you'll
very frequently hear them referred to as the vocalist muscles and the vocalist muscles
are going to when they contract add a little bit of lateral tension to the vocal ligaments
so they're going to um affect their shape so for instance if you were to look at a cross-section
of a vocal ligament like this when the vocalis muscle pulls on it that would transform
that into a thinner and flatter vocal ligament this is going to affect uh timbre or the
vocal quality of the sound or the tonal quality of the sound as it vibrates the uh the vocal fold
and the vocalist muscle owing to its ability to pull on the on the
vocal ligament also is going to finally adjust pitch so we've discussed the uh
the several intrinsic laryngeal muscles and what it means to be an intrinsic laryngeal muscle um
how that affects pitch by affecting vocal ligaments and how that affects
the airway by either narrowing or expanding the rima glottidis thank you very much for your time