hi let's talk about the larynx the larynx is colloquially referred to as the voice box because
within the larynx you have specialized folds called vocal cords that vibrate with exhalation
as air is moved over them the lyrics is a space is going to connect the pharynx or your throat
with your trachea so it's going to sit anterior to the larynx atop the trachea in terms of its
neurovasculature the larynx is supplied by superior and inferior laryngeal arteries
superior laryngeal arteries are branches of the superior thyroid artery of the external carotid
artery whereas inferior laryngeal arteries are branches of the inferior thyroid artery coming
off of the thyroid cervical trunk of the first part of the subclavian artery in terms of its
innervation the larynx is supplied by the vagus nerves it's supplied by superior branches called
the superior laryngeal nerves that come off of the vagus to supply the cricothyroid muscle as
well as the mucosa superior to the vocal cords and then there's the recurrent laryngeal nerves
that descends down to the root of the neck the right recurrent wraps around the subclavian artery
whereas the left recurrent laryngeal wraps around the concavity of the aorta before ascending back
up to the lyrics to innervate all of the remainder of the intrinsic laryngeal muscles as well as the
mucosa inferior to the vocal chords so the lyrics is comprised of several laryngeal cartilages and
these are largely hyaline cartilage but they do tend to calcify as people get older so in about
an individual's 30s is when they may begin to calcify so the most significant of the laryngeal
cartilages is the thyroid cartilage as we can outline here and the thyroid cartilage sits
atop the cricoid cartilage and it's somewhat obscured by the by the thyroid gland here but
the posterior we can see the laminae of the cricoid sitting there so those are two of
the larger cartilages there's also a rather large epiglottis cartilage that connects to the thyroid
that acts as a little leaflet that can aid in when people are swallowing material so that they don't
enter into the laryngeal Inlet sitting atop the cricoid cartilage are the are' tonight cartilages
a retinoid because they're shaped like a funnel and these are going to be significant because
the vocal ligaments which are the basis of the vocal cords attach between the vocal processes
of these are' tonight cartilages anteriorly to the thyroid cartilage sitting atop the arena
cartilages are the curricula cartilages they're also paired cuneiform cartilages that are embedded
in mucosa that you can't see here that help to maintain the laryngeal Inlet so here we can see
the larynx sectioned so the lyrics is supported from the hyoid by the thyrohyoid membrane and
this is a sagittal section of the larynx and so we have not just half a hyoid but we also have half
an epiglottis we have half of the thyroid there and then half of the cricoid but we get a better
sense of the cricoid cartilage here we can see the a retinoid cartilage and the critique youlet
atop it and probably most important we can see the vocal ligament running between the vocal process
of the arytenoid cartilage anteriorly to the thyroid cartilage now above that vocal ligament
is also a ventricular ligament that is going to form the basis for the ventricular or the false
vocal fold superior to the vocal ligament now with respect to the action of the lyrics there are a
couple of functions that it supports the first is swallowing and with respect to swallowing and this
is more a function that is supporting the action of the digestive system but because the pharynx
is a shared aerodigestive pathway what we need to do is close off the lyrics and that's going
to involve the elevation of the lyrics as well as the rotation of the epiglottis downward and
so that's going to happen there at the thyroepiglottic joint so that we don't have food materials
or liquids entering into the conductive pathway of the respiratory system the other functions of the
laryngeal cartilages are more in the wheel well of the lyrics itself and these are going to pertain
to breathing and vocalization they're going to be a couple of associations between cartilages
that are going to be important first associations between the areata noid and the thyroid cartilage
so what we're doing with this vocal ligament are we decreasing this space so that we decrease
tension or are we increasing this space so that we increase tension tension on the vocal ligament
is going to control pitch so the more tension the higher the pitch the lesser the tension the
lower the pitch we can also adjust what's going on between the arytenoid cartilages themselves or
between the arytenoids and the cricoid so the cricoarytenoid joint is interesting in that it
involves pivoting of the arytenoids so that we can either a be duct or a deduct the vocal folds
or we can slide the arytenoids closer to one another so that we can a deduct or bring those
vocal folds nearer to one another so there are two joints that are going to support the mission
of the lyrics in both breathing and vocalization and these are the cricothyroid joint or the joint
between the cricoid cartilage and the thyroid cartilage and this is a pivoting joint so what
happens and it's not Illustrated here but it's about there it's between the cricoid cartilage
and the inferior Horn of the the hyoid cartilage and what happens is this can pivot and that moves
the thyroid cartilage anteriorly and inferiorly and so this is going to increase tension on the
vocal ligament or if we rock it back that can decrease tension on the vocal ligament if we
return back to standard anatomical position with respect to the cricoarytenoid joint there are
a couple of things which we're capable of doing so the arete noids can pivot so they're pivoting
outward that way and as they pivot outwards they ABduct its abduction the vocal folds so this
is the position that is going to be supportive of breathing the other thing that we're able to
accomplish with the arytenoids is that we could rotate them the opposite direction so as to
ADduct or adduct the vocal ligaments or bring them into nearer approximation with one another
and this is going to be important for vocalization so the the vocal folds need to be close to one
another so that when they vibrate that you can produce speech you can also slide the arete
nodes towards one another that also helps with a deducting the arete nodes and the vocal folds so
let's take one by one these intrinsic laryngeal muscles and explore the actions that they perform
how that affects the cartilage how that affects the vocal ligament and what that does to sound so
let's start with cricothyroid the cricothyroid muscle runs between the cricoid cartilage and
the thyroid cartilage and as tension is applied to that muscle the thyroid cartilage rocks anteriorly
and inferior really and that's going to put more tension on the vocal ligament so that's going to
increase pitch the cricothyroid muscle is the only intrinsic laryngeal muscle that's not innervated
by the recurrent laryngeal branch of the vagus in fact it's innervated by the external branch
of the superior laryngeal nerve next up we have a very important set of muscles called the posterior
cricoarytenoid muscles so these are between the cricoid cartilage and the areata noid cartilages
these rotate the arytenoid cartilages so they they pull them that way and that ABducts the
vocal ligaments when the vocal ligaments are a deducted were able to move air at its maximum
capacity through the larynx so this this is a muscle of of respiration or ventilation and
these are controlled by the recurrent laryngeal nerve and sometimes I find that it is it's a
little disconcerting that we only have one pair of muscles that are aiding in maintaining a patent
airway but here they are when viewed from the posterior across there you've got one on either
side supporting the patency of the airway we have several sets of muscles that a deduct the vocal
folds to that are very closely related are the transverse and the oblique a retinoid muscles the
transverse and oblique arytenoid muscles can be seen here the transverse muscles have transverse
fibers whereas the oblique have oblique fibers and these are good at both gliding the areata noid
cartilages together so as to a deduct the vocal ligaments for vocalization there are also parts
of the oblique areata noid that are important for drawing down the vocal Inlet so as to to make that
smaller both of these muscles are innervated by the recurrent laryngeal nerve we also have lateral
cricoarytenoid muscles so cry co because they originate on the cricoid cartilage are annoyed
out to the muscular process of the areata noid cartilages these muscles are going to rotate the
arena cartilages and when they do that brings the vocal ligaments into closer approximation or it
will adduct the vocal folds for vocalization and these muscles are also controlled by the recurrent
laryngeal nerve and then finally we have muscles that span between the areata cartilages and the
thyroid cartilage these are called Thyroarytenoid muscles now generally the thyroarytenoid
muscles are going to pull the arytenoid cartilages forward and in so doing they're going to decrease
pitch but there are also specialized fibers of the thigh row a retinoid muscle located here and
here immediately adjacent to the vocal ligaments that are capable of finally adjusting tension on
the vocal ligament and sometimes even pulling on the vocal ligament laterally so as to change
the mass of the vocal ligament this both allows the muscle to finally adjust pitch and change
Tambor as well and these are known as vocalist muscles some sources consider vocalist muscles
their own individual muscles and some consider them specialized fibers of thyroarytenoid muscle
however both of these muscles are in the same locations and are innervated by the
same recurrent laryngeal nerves when we look at the larynx and here is a view of the larynx from
the the posterior and it's been opened along the midline so this has been cut and the edges have
been a be ducted away we're able to see the the various spaces of the larynx and so here's the
epiglottis cartilage there and when air enters into the lyrics are comes out of the lyrics it
goes through the laryngeal Inlet and it enters the vestibule from the laryngeal vestibule we could
descend inferiorly into a space called the rima vestibuli the rima vestibuli is the space
between these false vocal cords the false vocal cords don't vibrate during vocalization but they
can vibrate to produce a sound so if you've ever heard of throat singing that's the vibration
of the false vocal cords so let me give you a an example of this oh those are my false vocal cords
not my true vocal cords so that's something that you can perform at home so that you can feel what
it's like to vibrate those as we move inferior ly passed the the rima vestibuli there's
the laryngeal ventricle so this is the space between the vestibular or ventricular or false
vocal folds and the vocal folds are the true vocal folds so the false vocal folds are above and the
true are below and between them is the ventricle from the ventricle we're then in the space called
the rima glottidis and so the rima glottidis plus the true vocal folds is called the glottis
and then the space below the glottis is called the infra glottic cavity and the infra glottic cavity
is going to extend down to the bottom of the cricoid cartilage and it's going to be continuous
with the trachea so we've talked a little bit about the lyrics and its role in breathing
and sound production we've talked about its cartilages its muscles and its spaces thank you