this is dr fox let's talk about the larynx in this video we'll discuss the larynx and the major
cartilaginous parts of the laryngoskeleton and relate any important features of those cartilages
to the structure and functions of the larynx the larynx is colloquially known as the voice box
it sits inferior to the hyoid bone which is there to which it's connected by the thyrohyoid membrane
it's named such because that membrane runs between the thyroid cartilage which is a major
constituent of the larynx and the hyoid bone 4x sits anterior to the laryngopharynx which would be
the portion of the pharynx which is about there and that is contiguous with the esophagus
and it sits proximal to the trachea which is that conductive pathway to the conductive pathways of
the lungs and the larynx is connected to the trachea via the cricotracheal ligament that
runs between the cricoid cartilage of the larynx and the trachea we tend to relate structures to
their relative positions of various elements of the vertebral column and for the larynx
we estimate that it sits approximately between c4 and c6 levels of the cervical spine
let's take a look at some of the constituent cartilaginous parts of the larynx
so the larynx is largely comprised of hyaline cartilage elements that we refer to as the
laryngoskeleton now the major portions of the laryngoskeleton are the thyroid cartilage the
cricoid cartilage epiglottic cartilage and the arytenoid cartilages which are paired as we'll see
there are a few other minor paired cartilaginous elements but they won't be the focus of this video
let's take a look at these structures so i'm outlining now the thyroid cartilage
that thyroid cartilage is a very prominent anterolateral cartilage of the
larynx looking at this posterior view we see that the thyroid cartilages
are incomplete posteriorly the cricoid cartilage which i am circling now
see here is the only portion of the laryngoskeleton which is complete
360 degrees around the airway the epiglottic cartilage in profile here in lateral view we
can see it just tipping out there is a little more obvious when viewed from the posterior
has a stem and leaf-like appearance to it and then the arytenoid cartilages
sit atop the cricoid cartilages they're more sort of cone or funnel shaped
we're going to see those are going to be very important cartilages with respect to the functions
of the larynx so let's take a look at some of the features of these major cartilages so the
thyroid cartilage consists of two laterally placed laminae or sheets and there's one lamina there and
the other meets it along the midline there there is a laryngeal prominence
which is located there that's a palpable landmark so if you take a a finger or two and palpate
the uh the midline or the the median of your neck you can palpate that laryngeal prominence
that laryngeal prominence tends to be even more prominent in individuals with higher levels of
testosterone there are two sets of horns there is a superior horn and that is going to come
very near to the greater horn or cornua of the hyoid bone and then there is an inferior horn
that inferior horn is going to form a joint with the cricoid cartilage
the cricothyroid joint and that's going to allow for a pivoting motion of the
thyroid cartilage which we'll see in a little bit
that cricoid cartilage as i've said is the only element of the laryngoskeleton which is complete
360 degrees about the airway it's going to form a base upon which the arytenoid cartilages
sit and there is also the epiglottic cartilage which articulates with the thyroid cartilage
and that's going to help along with the arytenoid cartilage form the laryngeal inlet
jill inlet
that's the space into and out of which air is going to flow between the larynx
and the laryngopharynx
the retinoid cartilages are some of my favorites they're really you know under noticed but
high value high roi cartilages they sit atop the cricoid cartilage like so and they are controlling
both the laryngeal inlet and what specific folds within the larynx called the vocal folds are
doing so we can see the original cartilages from the superior here one is there and one is there
most of but not all but most of the intrinsic laryngeal musculature are going to control what
these arytenoid cartilages are doing and they will have muscular processes sort of posterior
laterally here those muscular processes allow the intrinsic laryngeal muscles to move the arytenoid
and anteriorly there are also vocal processes those vocal processes are going to allow the
vocal ligament to connect between the arytenoid cartilage and the anterior portion of the
thyroid cartilage and so those vocal ligaments are invested by mucosa to form vocal folds
also known as your vocal cords and when the arytenoid cartilages move those vocal ligaments
can abduct or abduct so as to open up so as to open up the airway or they may adduct adduct
so as to narrow the airway and that's the position for phonation we won't get into the details of all
of the intrinsic laryngeal muscles we'll just show you a few exemplars here and the first
are going to be the posterior cricoarytenoid muscles so posterior gives you an idea of where
these are located and crico-arytenoid gives you an idea of the attachments
so the posterior cricoarytenoid muscles attached to the posterior aspect of the cricoid cartilage
and they come up and they attach to the muscular processes of the arytenoid
cartilages and they're going to predominantly laterally pivot the arytenoid cartilages so when
they pull back like so that causes the arytenoid cartilage to laterally pivot
and that is responsible for adduction of the vocal fold or a more open airway for ventilation
these posterior cricoarytenoid muscles are innervated by branches of the vagus nerve cranial
nerve X known as the recurrent laryngeal nerves another exemplar muscle is the cricothyroid muscle
the cricothyroid muscle is best viewed anteriorly and laterally and the cricothyroid muscle
acts upon that cricothyroid joint and so when the muscle is activated that's going to pull
the thyroid cartilage anteriorly and inferiorly so it tips it forward at that joint when it
tips it forward that is going to put tension on those vocal folds the vocal cords that's going
to increase pitch or tension equals elevated pitch the cricothyroid muscles are innervated by another
branch of the vagus nerve called the superior laryngeal nerve specifically the external branch
of the superior laryngeal nerve the internal branch of the superior laryngeal nerve is going
to be sensory from the mucosa superior to the vocal folds but the external branch is going to be
efferent or motor to this cricothyroid muscle all of the other intrinsic laryngeal
muscles are innervated by the recurrent laryngeal
nerve so this is a fantastic exception to the innervation of the intrinsic laryngeal muscles
clinical item of note here is that the larynx is a region where you may access the airway
in an emergent situation by performing something known as a cricothyrotomy a cricothyrotomy
is the incision of the skin and the underlying median cricothyroid ligament
sometimes rather unempathetically referred to as a 'crike' this procedure may be done in order to
gain access to the airway in an emergent situation and how that is performed is you would palpate the
laryngeal prominence there you go just below the laryngeal prominence you can also palpate the
cricoid cartilage so if you put your finger along the midline of the neck you can palpate first that
laryngeal prominence next the cricoid cartilage and between them is going to be a soft spot that
soft spot is the median cricothyroid ligament so you would incise the skin and then you would
incise the cricothyroid ligament there and you may cannulate so as to maintain an airway
what's nice about this procedure is that there are very excellent palpable landmarks
and there are no major vascular obstacles that you can perforate in performing it
this is not a long-term solution to managing an airway but it will do in an emergency situation
so we've discussed the larynx and its constituent cartilages and their major features and we've
talked a little bit about how various intrinsic laryngeal muscles can affect that laryngoskeleton
this is your summary slide thank you for your time