Speech Anatomy&Physiology SPPA 2050
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SPPA 2050 Speech Anatomy and Physiology CHAPTER V PHONATION The larynx is a funnelshaped arrangement of cartilage connective tissue and muscle slightly wider above than below that spans a space in the neck stretching from roughly the 3ml to the 6th cervical vertebra The larynx is ventral to the spine and esophagus caudal to the pharynx and sits on top of the trachea forming a valve whose main function from a phylogenetic or evolutionary perspective is to protect the lower airway As we did with the respiratory system we will begin by learning the skeletal structure of the larynx We can reasonably break this down into the l cartilages 2 joints that connect the cartilages and 3 ligaments and membranes that hold everything together In one sense the larynx is an easier structure to study because it is more selfcontained than the large and cumbersome respiratory system The Cartilages and maybe a bone A lot of what you will learn later about laryngeal anatomy and physiology follows from this set of information and especially the names of the cartilages It is important that you memorize these early and use them often in conversations with your friends Cartilages rather than bone provide the skeleton of the larynx At the outset of any description of the cartilaginous skeletal framework of the larynx it is customary to mention the delicate albeit important horseshoeshaped hyoid bone that is rostral to the main body of the larynx Key landmarks include the body lesser cornu cornu horn and greater cornu The hyoid bone is a site of attachment for many key muscles of the head and neck Many authorities do not include this bone as part of the larynx proper though we can reasonably include it and all relevant muscles and connective tissues as apart of something we might call the hyo laryngeal complex If the hyoid is part of the larynx it is its only bone If not then the larynx is still safely bonefree We usually say that there are six cartilages by name in the larynx Three are unpaired only one of them and three are paired two of them like lots of things in the body making a total of nine cartilages The rst four three unpaired and one paired ve total are very important for understanding laryngeal structure and function Know these cold Learn them as soon as possible since our knowledge literally builds on them The other cartilages are included for completeness and you will not be responsible for them In descending order of their size these six are 1 unpaired thyroid shaped something like a butter y The thyroid cartilage is the most rostral of the laryngeal cartilages It has two laminae the wings of our butter y joined ventrally in the midline at the angle usually visible through the skin of the neck of a skinny guy and superior and inferior cornu ie horns Distinctive thyroid landmarks include the oblique line on either lamina and the superior thyroid notch easily palpated at the rostral margin of the thyroid angle the socalled Adam s apple The thyroid is quotclosedquot ventrally at the angle where the two laminae meet but open in the back like the everpopular hospital gown 2 unpaired cricoid shaped something like a signet ring The ringlike cricoid is the foundation of the larynx and thus is its most caudal component It is tied to the rostralmost tracheal ring by a relatively stout cricotracheal membrane Its dorsal quotfacequot ie the quotsignet partquot of the ring is sometimes referred to as the lamina while its shorter ventral portion is often referred to as the arch The lower horns of the thyroid laminae straddle the cricoid joining its lateral margins at articular facets forming a pivotlike cricothyoid joint 3 unpaired something like a leaf The rostral margin of the epiglottis eXtends above all other laryngeal cartilages though the cartilage itself quotoriginatesquot below the rostral margin of the thyroid where it is tied to the thyroid by the thyroepiglottic ligament at a pointlike thyroepiglottic joint just caudal and dorsal to the superior thyroid notch It is possible to glimpse the upper margin of the epiglottis with the nekkid eye especially in young babies but even in adults given suitable oral gymnastics wild tonguepulling and the like epiglottis shaped 4 paired arytenoids shaped something like four sided pyramids These articulate with the cricoid at cricoarytenoid joints formed about saddle shaped facets that run laterally caudally and ventrally along the rostrolateral margins of the cricoid lamina Each facet on either side of the cricoid is conveX upward from the point of view of the cricoid and matches a corresponding concave upward facet on the under surface of the arytenoid Each arytenoid has four vertices or comers The lateralmost is typically called the muscular process the ventralmost is typically called the vocal process and the comer that points in the rostral direction is typically called the SPPA 2050 Speech Anatomy and Physiology apex The remaining cartilages are not critical to our understanding of laryngeal function I include them simply for completeness but will not be included in any testing 5 paired corniculates shaped something like miniature arytenoids Each corniculate joins the apeX of its corresponding arytenoid though there is no motion about these joints 6 paired and possibly inconsequential cuneiforms shaped something like little bullets The cuneiform cartilages are quotlost in spacequot in the sense that they do not articulate with any other laryngeal cartilages Instead they are suspended in the rostralmost border of the quandrangular membrane which eXtends caudally and dorsally from the lateral margins of the epiglottis to the lateral margin of each arytenoid on the same side of the larynx The rostral border of this membrane is given a special name the aryepiglottic fold The open area medial to the left and right margins of the aryepiglottic fold and dorsal to the surface of the epiglottis is usually referred to as the laryngeal aditus ie entryway or opening Three of the laryngeal cartilages by name thyroid cricoid and arytenoid are formed from a type of cartilage we call hyaline These will ossify turn to bone in time The other three cartilages by name epiglottis corniculate and cuneiform are merely and always elastic in nature Laryngeal Joints In the larynX there are a number of important joints at the intersections ie articulations of some pairs of cartilages After you ve learned the names of the cartilages understanding the joints is much easier since their names are often derived rom the structures that form the articulation The thyroepiglottic joint is found at the point of articulation between the thyroid and the stem of the epiglottis The cricothyroid joint is found where the lower horns of the thyroid straddle and contact the lateral margins of the cricoid And the paired cricoarytenoid joints are found where the arytenoids rest atop the upper lateral margins of the cricoid lamina The motions oflaryngeal cartilages about their respective joints provide mechanisms for the principal functions of the human larynx The epiglottis for example seems to pitch see NOTE below about the pointlike thyroepiglottic joint obstructing the laryngeal opening technically called the aditus during swallowing and protecting the airway from ingestion of foreign matter foodstuffs swords re and the attendant pneumonia aspiration pneumonia that comes from inspiring what should not be inspired Similarly the thyroid cartilage pitches about the twopoint pivotlike cricothyroid joint stretching the vocal folds attached to the dorsal surface of the thyroid angle in turn regulating perceived pitch of the voice for speech andor stiffness of the vocal folds again useful in preventing wrong things from going down the wrong tube Finally each arytenoid pitches and rolls about its corresponding cricoarytenoid joint and may translate slide along the length of the articular facet These motions of the arytenoids allow intricate control of the size of the glottis the name for the space between the vocal folds and also of the mechanical properties of the vocal folds SPPA 2050 Speech Anatomy and Physiology NOTE It is an interestingfact to remember that all laryngeal cartilages are three dimensional objects In principle in a three dimensional world any object bigger than a virtual point is capable ofmovements that may involve up to six degrees offreedom These include rotation about any of the three axes associated with the three dimensional reference frame pitch about a dextral sinistral axis roll about a dorsal ventral axis yaw about a rostral caudal axis andor translation e ectively quotslidingquot along lines parallel to any of the three reference axes No movement of any laryngeal cartilage about its respective mobile joint involves more than three degrees of freedom This general fact is due partly to the design of each joint eg the placement shape andor location of relevant articular facets and partly to the many ties that bind these cartilages together These ties are the ligaments and membranes of the larynx and will be discussed next Ligaments and membranes L amp M Laryngeal cartilages are interconnected by a rich complicated set of ligaments and membranes For a variety of reasons it is possible to argue that these ligaments and membranes hereafter L amp M are as important for laryngeal function especially for speech as are the cartilages they connect and the muscles that move those cartilages No doubt Ls amp Ms keep parts of the larynx from ying apart unexpectedly while you sleep at night Thank goodness for that But these ties also clearly constrain the dimensionality of movements that occur about the joints Consider for example the L amp M set that affects the epiglottis Ventrally this cartilage is bound to the tongue by the median and lateral glossoepiglottic folds and to the body of the hyoid bone by the hyoepiglottic ligament Dorsally and caudally the epiglottis is bound to the arytenoid complex by the quadrangular membranes which terminate rostrally in a thickened fold of tissue known as the aryepiglottic fold Finally the epiglottis is bound to the thyroid at the point of the joint by the thyroepiglottic ligament Given these relatively many ties it is clear that the epiglottis cannot translate with respect to the thyroid and it is difficult to imagine that any roll or yaw rotation about body axes would be possible About the only plausible epiglottic movement we might expect would involve a pitching motion about the point of contact between the epiglottis and thyroid Apparently something like this occurs during swallowing In highspeed cineradiographic and video uorographic images of swallowing the epiglottis appears to pitch rearward covering the aditus as the larynx as a whole is raised and forced against and under the lower rear of the tongue A pitching motion of this type would be possible as long as the epiglottic Ls amp Ms are not stretched beyond their resting length Ligaments especially cannot be stretched much before they rupture or tear loose from their bony and cartilaginous anchor points Those who have suffered ACL anterior cruciate ligament injuries involving the knee develop an understanding of this feature of ligament in a personal and painful way In effect the general function of ligaments in the body is to anchor the components of joints and limit their motion with respect to one another The thyroid cartilage is tied directly to three laryngeal cartilages to the epiglottis see above to the cricoid cartilage by l the conus elasticus including its thickened medial and lateral portions often referred to as the median and lateral cricothyroid ligaments and 2 the ceratocricoid ligaments at each of the cricothyroid joint articulations The thyroid is also tied to the arytenoids by yet another portion of the conus elasticus typically referred to as the vocal ligament The ceratocricoid ligaments in particular would seem to prevent motions of the thyroid eg roll yaw or translation in any direction in any sense other than a simple pitching motion about an axis drawn through the right and left cricothyroid articulations Finally the thyroid is tied to the hyoid bone by the thyrohyoid membrane whose thickened medial and dorsallateral portions are often referred to naturally enough as medial and lateral thyrohyoid ligaments Together these thyrohyoid Ls amp M form a continuous sheet of connective tissue that spans the entire space between the horns and caudal and rostral margins of the hyoid and thyroid wrapping from one side of the larynx to the other The cricoid cartilage is tied by L amp M to the rostralmost tracheal ring by the SPPA 2050 Speech Anatomy and Physiology cricotracheal membrane Along its dorsal lamina the cricoid is attached to the arytenoids by the posterior cricoarytenoid ligaments These are not shown in any of the gures though such ligaments are typically shown in other texts running between the dorsal lamina of the cricoid near the cricothyroid joints and the dorsocaudal margin of each arytenoid Presumably these latter ligaments restrict motion of the arytenoids relative to the cricoid at least in extent if not direction However the facets on the cricoid and arytenoid cartilages at their articulation probably exert a stronger in uence on possible motion than do the connecting ligaments limiting motion of the arytenoids to a type of pitching and rolling rotation supplemented by some translation along the quotlengthquot of the joint surfaces We will discuss these actions in detail later Your burden is to simply know that such ligaments exist Finally the ventricular folds and ventricles cover the inside of the larynx above the glottis We will discuss these structures in more detail later Most inferences we can draw about possible motions of cartilages at the laryngeal joints must be evaluated in the context of relevant lines of action of muscles that act on or quotacrossquot the joint components It is for this reason that each student of laryngeal anatomy must learn the names origins insertions and actions of muscles affecting the larynx Fortunately this chore is not so difficult for the larynx as it may have seemed for the respiratory system In general muscles that affect the larynx are divided into two main classes those we refer to as intrinsic to the larynx and those we refer to as either extrinsic or supplemental The names of the large majority of muscles in both groups are transparent in the sense that they re ect and indicate the names of cartilages they interconnect SPPA 2050 Speech Anatomy and Physiology Intrinsic Laryngeal Muscles The intrinsic laryngeal muscles get the intrinsic part of their name from the fact that they interconnect various pairs of laryngeal cartilages and thus have both their origins and insertions quotinsidequot the larynx The contractions of these muscles as a group regulate vocal fold position and tension These two variables determine whether and how the vocal folds vibrate during speech and song We will emphasize ve main intrinsic laryngeal muscles though some teth will identify more eg by subdividing bers quotbelongingquot to one muscle some say into two or more different muscles they say The most common names given to the ve most commonly identi ed intrinsic laryngeal muscles re ect directly the various pairs of cartilages they connect 1 cricothyroid C7 joining the cricoid and thyroid 2 lateral cricoarytenoid LCA joining the cricoid and arytenoids 3 posterior cricoarytenoid PCA joining the cricoid and arytenoids 4 thyroarytenoid TA joining the thyroid and arytenoids medially by vocalis bers more laterally by thyroarytenoid 5 interarytenoid IA or simply arytenoideus joining the arytenoids with transverse and oblique bers It is important to note that the names of the fourth and fth muscles in the preceding list differ somewhat from the terminology in Netter It is also important to note that some texts expand the list of intrinsic muscles by illustrating and emphasizing relatively sparse ber bundles Two examples include the aryepiglottie muscles whose bers connect each arytenoid to the corresponding lateral margin of the epiglottis and the thyroepiglottie muscles whose bers connect the quadrangular membrane andor lateral margin of the epiglottis to the medial surface of the corresponding thyroid lamina We will not focus any attention on these muscles in lecture By convention we often refer to the ve main intrinsic laryngeal muscles merely by abbreviations shown in parentheses that suggest their names Applying this convention in conversation or writing is OK as long as our communicative partners understand that a laryngeal context applies to each reference We must keep in min that there are other muscles distributed about the body whose names could be abbreviated in the same way as the intrinsic laryngeals eg the everpopular transversus abdominis yet another TA For the time being take the time to learn both the muscle names and their corresponding abbreviations Muscle names spelled out minimize any chance for ambiguity The rst four muscles in the preceding list are paired ie there is one of each type on either side of the midline of the body The interarytenoid IA or at least its bundle of transverse bers is the only unpaired muscle in the list Typical illustrations show a single body of transverse bers crossing the midline joining the arytenoids However some sources including Netter subdivide the A into two muscles the unpaired transverse interaryten0id and the paired oblique interaryten0id muscles In texts where this distinction is drawn we must count the latter as paired since there are distinct bundles of bers that cross obliquely from the dorsocaudal aspect of the muscular process of each arytenoid to the rostral apex of the opposite arytenoid Notes on naming variations of TA and CT Interestingly or not depending upon your tolerance for relatively ne anatomic details some texts will also subdivide each right and left belly of what I refer to as the TA muscle into a medial part called the thyrov0ealis closest to the free edge of each vocal fold and a more lateral part called the thyromuseularis or merely the thyroarytenoial Other texts merely mention a single muscle called the TA Still others may also refer to a single muscle but give that muscle mass another name eg the vocalis muscle abbreviated VOC Finally you should be aware of the fact that we sometimes subdivide each right or left CT belly into two distinct units referred to as the dorsal oblique part and ventral straight or recta part It is easy to get the feeling from these last few examples that a whole lot of slicin n dicin could go on about whether any speci c muscle in the body is one or several SPPA 2050 Speech Anatomy and Physiology functional units Why the variation from one text to the next Fashions even in anatomy come and go New information may be uncovered and certainly new analytic traditions can impose different emphases even on facts long known The modern trend to think of each vocal fold as a complicated structure made up of different tissue layers each differently sensitive to muscular and aerodynamic forces generated during speech may suggest why modern teth tend to quotseequot separate muscles in the mass of muscle bers connecting each vocal process of each arytenoid to the inner surface of the thyroid angle Extrinsic Laryngeal Muscles The extrinsic laryngeal muscles get the rst part of their name ie extrinsic from the fact that they connect various laryngeal cartilages to structures outside the larynx ie hyoid bone sternum Each of the quotextrinsicsquot has one attachment and whether we call that attachment an origin or insertion doesn t much matter in the larynx on one of its cartilages and one attachment outside the larynx I like to use what I call a foot metaphor to emphasize a key anatomical distinction between intrinsic and extrinsic laryngeal muscles Each intrinsic laryngeal muscle has both its origin and insertion ie both its quotmuscular feetquot on laryngeal cartilages and thus in the larynx Each extrinsic laryngeal muscle has only one muscular foot in the larynx Of course by de nition the other foot must be elsewhere The intrinsic laryngeal muscles as you should recall are mainly responsible for regulating positioning and tension of the vocal folds We might say that at least both of the extrinsic laryngeal muscles identi ed below are responsible for regulating vertical position of the larynx in the neck We also suspect that extrinsic laryngeal muscle contractions may indirectly and inadvertently affect vocal fold tension by tugging and stretching various membranes and ligaments that tie parts of the larynx together However we do not believe that regulating vocalfold tension is a primary responsibility of the extrinsics Two extrinsic laryngeal muscles with names that directly re ect their laryngeal and extra laryngeal attachments are l sternothyroid joining the sternum and thyroid 2 thyrohyoid joining the thyroid and hyoid Other extrinsic laryngeal muscles 7 eg the socalled thyropharyngeal andor cricopharyngeal subdivisions of the inferior pharyngeal constrictor muscle 7 may be identi ed by authors of some texts The two muscles listed above as l and 2 are your only current extrinsic laryngeal responsibilities in quotmyquot book Supplemental Laryngeal Muscles There is a group of muscles that are often grouped with the extrinsic laryngeal muscles which I will call supplemental laryngeal muscles This is a subclass of muscles whose contractions might also affectregulate height of the larynx in the neck These muscles are probably responsible for other things as well Unlike the intrinsic or extrinsic laryngeal muscles none of these muscles has an insertion or origin directly on any laryngeal cartilage Thus I sustain the foot metaphor by pointing out that all supplementals have both feet outside the larynx One attachment will be in the vicinity of the hyoid bone and one attachment elsewhere eg to the base of the skull the lower jaw the sternum or even the scapula Supplemental laryngeal muscles whose names are not as transparently quotfriendlyquot as the names of most intrinsic and extrinsic laryngeal muscles and which muscle therefore be memorized include 1 digastric muscle with its anterior belly joining the hyoid bone and mandible and posterior belly joining the hyoid and temporal bones mastoid 2 stylohyoid joining the hyoid and temporal bones styloid process 3 mylohyoid joining the hyoid bone and mandible 4 geniohyoid joining the hyoid bone and mandible 5 hyoglossus joining the hyoid bone and the tongue 6 sternohyoid joining the hyoid bone and sternum manubrium 7 omohyoid joining the hyoid bone and scapula All supplemental and extrinsic laryngeal muscles are paired From a mechanical point of view we can guess that the contractions of those supplementals with an attachment above the hyoid muscles we call suprahyoid may collectively assist in elevating the larynx along the length of the neck essentially by tugging on the hyoid bone Conversely all supplementals with an attachment below the hyoid muscles we call infrahyoid may help depress the larynx Together the stemothyroid sternohyoid and omohyoid muscles are sometimes called quotstrapquot muscles SPPA 2050 Speech Anatomy and Physiology The worksheet that appears on the following page is very much like your other Muscle Worksheets These worksheets are intended as study guides Hopefully they help you extract and organize key information about muscles we believe to be important for speech production As with the other muscles you will be expected to know the names origins insertions mechanical actions and motor supply for the muscles in the various intrinsic extrinsic and supplemental muscle worksheets For the intrinsic laryngeal muscles you should emphasize the effects of contractions on positioning adduction or bringing togetherabduction or moving apart and tension of the vocal folds For the extrinsic and supplemental laryngeal muscles you should emphasize the effects of contractions on positioning of the larynx in the neck It is reasonably clear to me that the laryngeal supplementals especially the suprahyoid group has main actions that are probably not laryngeal The anterior digastric and geniohyoid for example are key depressors of the mandible However their contractions may affect the larynx via indirect links through the quotthyrohyoid complexquot of ligaments and membranes For now we learn the mechanical actions related to moving the larynx Later we will review these same muscles and their mechanical action on another structure mandible The good thing is that the attachments and motor supply don t change so you ll only have to learn that once As you learn the muscles related to the larynx and other structures for that matter it is good practice to trace with your nger or eye the motor lines to muscles shown in Netter s plates Doing that seems to help cement the information A few words about quotLaryngeal Geographyquot If we take a coronal section through the larynx we obtain an outline that looks something like an hourglass wide above in the vicinity of the laryngeal aditus and below in the vicinity of the ligamentous connection between the caudal margin of the cricoid cartilage and the rostralmost tracheal ring and narrow in the middle Unlike the hourglass the narrowed middle region of larynx corresponds to a spatially close pair of constrictions formed by two quotshelvesquot of tissue The caudal shelves projecting medially from dextral and sinistral sides of the larynx are the true vocal folds while the rostral shelves are most commonly referred to as the ventricular folds though sometimes the phrase false vocal folds is used In a rostralcaudal direction the two sets of shelves are separated by a slightly widened space known as the laryngeal ventricle The area rostral to the ventricular folds is usually referred to as the laryngeal vestibule Any area caudal to the true vocal folds is simply known as the subglottal region The ventricular folds separated by a space in the dextralsinistral direction called the ventricle are fairly simple in their construction composed mainly of undifferentiated ligamentous connective tissue covered along the most medial aspect projecting into the airway by a thin mucosal membrane The vocal folds separated also in the dextralsinistral direction by a space usually called the true glottis other times called the rima glottis or rima glottidis are somewhat more complex in their construction containing at least three layers 1 muscle bers in their most lateral aspect belonging to the thyroarytenoid and vocalis muscles Netter s terminology 2 ligamentous tissue derived from a specially thickened portion of the conus elasticus in their middle portion and 3 a mucosal cover along their most medial aspect extending farthest into SPPA 2050 Speech Anatomy and Physiology the airway The vocal ligament is typically subdivided further into three layers the super cial layer comprised of mainly loose connective tissue the intermediate layer comprised primarily of a stretchy material called elastin and a deep layer which is comprised of stiff collagen bers In some texts even more layers are identi ed in each vocal fold on the basis of ne structure distinctions exposed in histological analyses Exactly how many layers there are in each vocal fold is not as important as the idea that each fold is composed of layers and the related fact that at least one of these layers is muscular Ventrally the vocal folds are attached to the dorsal surface of the thyroid angle Dorsally they are attached to the arytenoids distributed along a quotlinequot running from the vocal process to the muscular process of each arytenoid Thus any muscle contractions that affect the positions of the thyroid andor arytenoids will also affect the positioning andor stiffness of the vocal folds In and of itself the fact that the vocal folds themselves are composed partly of muscle also means that they can be contracted and quotstiffenedquot or tensed Stiffening the vocal folds will affect whether and how they will vibrate when they do during speech In general we usually say that the main speech job of the class of intrinsic laryngeal muscles including but not limited to the thyroarytenoid andor vocalis muscles if they are differentiated is to regulate positioning and tension of the vocal folds and to a large degree their propensity for vibration It is noteworthy that there are no muscles in the larynx that regulate independently the position andor tension of the ventricular or false vocal folds SPPA 2050 Speech Anatomy and Physiology Motor Supply for Muscles Affecting the Larynx The corresponding worksheets provide motor supply information for intrinsic extrinsic and supplemental laryngeal muscles There is little argument about the motor supply for the intrinsic laryngeal muscles If you reviewing different anatomy texts you may get slightly different motor supplies for some of the extrinsic and supplemental muscles Determining motor supply can be a relatively messy business especially when the nerves that are involved are quothigh levelquot Nerves high in the body are often quotguilty of cominglingquot Remember the dirty word plexus That is the reason different texts may seem to say something different from information in the following list at least for some muscles Intrinsic laryngeal muscles All ve intrinsic laryngeal muscles TA IA LCA PCA CT are supplied by Cranial X Vagus Most texts and Netter is no exception make the point that the rst four muscles from this list of ve ie excluding the CT are supplied by what we typically refer to as the recurrent laryngeal nerve The CT in contrast is supplied by the external branch of the superior laryngeal nerve You may be curious about terminology in the preceding three sentences Why for example do we say that the intrinsic laryngeal muscles are supplied by the Vagus and in the next breath talk instead about recurrent and superior laryngeal nerves The answer has to do with a naming convention applied to the major subdivisions of the Vagus that contain efferent motor bers Note that Netter always uses solid red lines in his drawings to indicate such quotmotorquot lines Where distinctions are drawn solid blue lines always represent afferent tracts One can think of the Vagus nerve as the main interstate with a number of exits ie nerve branches with particular names that head to and supply nearby structures If you study various plates of Netter you will see the branching of the Vagus Just caudal to the bulbous inferior ganglion you can see rst a pharyngeal branch that leaves the main trunk fanning out to supply muscles affecting the soft palate eg palatoglossus palatopharyngeus and the pharynx eg superior middle and inferior pharyngeal constrictors Somewhat below this pharyngeal branch you can see next the superior laryngeal nerve as it departs what remains of the main trunk of the Vagus splitting into a sensory afferent internal branch and a motor efferent external branch The latter of the superior laryngeal nerve branches as promised the external branch of the superior laryngeal nerve supplies the cricothyroid CT muscle Yet a third main branch of the Vagus which we call the recurrent laryngeal nerve which loops down under and behind the aorta on the left side not so low but still behind the carotid and subclavian arteries on the right side nally ascending back up to the larynx The recurrent laryngeal nerve pass beneath the inferior pharyngeal constrictor muscle dorsal to the cricothyroid joint on either side of the cricoid and then medial to the respective lamina of the thyroid cartilage to supply the other four intrinsic laryngeal muscles eg the TA IA LCA and PCA An interesting anatomical oddity associated with motor supply for these four intrinsic laryngeal muscles is this Trauma to either of the recurrent laryngeal nerves say from carotid artery or thyroid gland surgery or an aortic aneurysm may cause functional laryngeal de cits eg perceptible hoarseness breathiness andor quotroughnessquot of the voice Extrinsicsupplemental laryngeal muscles The motor supply entries for these muscles can be found in the worksheet for extrinsicsupplemental muscles