Larynx Anatomy Notes PDF

Human Gross Anatomy & Radiology I Larynx Objectives By the completion of your study of the larynx you should be able to: 1) Describe the laryngeal cartilages including their named parts. (II.)...

Human Gross Anatomy & Radiology I Larynx Objectives By the completion of your study of the larynx you should be able to: 1) Describe the laryngeal cartilages including their named parts. (II.) 2) Define the ligaments and joints of the larynx, and understand the relationships of the laryngeal cartilages and associated structures with one another in intact specimens. (III. & IV.) 3) Explain the various openings, divisions and extensions of the laryngeal cavity. (V.) 4) Differentiate the intrinsic muscles of the larynx (e.g. location, attachment sites, and functions). (VI.) 5) Explain the arterial supply and venous and lymphatic drainage routes for the larynx. (VII.) 6) Describe the innervation of the larynx including sensory, motor, and autonomic routes and any associated functional changes relative to damage of these innervations. (VIII.) Resources Acland Videos: 4.5.3 4.5.4 4.5.5 1 Larynx I. Overview The larynx… A. is continuous with the pharynx posteriorly and superiorly, and with the trachea inferiorly. B. is located at vertebral body levels C3-C6 and medial to carotid sheaths and thyroid glands C. functions to… 1. allow passage of air through the respiratory tract, 2. serve as a sphincter to close off respiratory tract during swallowing or to restrict expiration 3. produce phonation (voice sounds) II. Laryngeal skeleton  The skeleton is formed by nine cartilages; three singles and three paired.  All are formed by hyaline cartilage, with the exception of the epiglottic cartilage and other small areas formed by elastic cartilage.  The hyoid bone is connected to the larynx by various extrinsic ligaments/membranes, but is not considered as a formal component of the larynx A. Thyroid cartilage 1. largest of the laryngeal cartilages (single piece) 2. consists of two quadrangular laminae fused anteriorly (with the laryngeal prominence (Adam’s apple)) and open posteriorly 3. a V-shaped superior thyroid notch is found above the laryngeal prominence 4. bilaterally at the posterior margins, superior cornua (horns; cornu singular) project superiorly and the inferior cornua project inferiorly, articulating with the cricoid cartilage 5. the oblique line is a ridge on the posterolateral sides of the laminae for sternothyroid, thyrohyoid, and inferior pharyngeal constrictor muscle attachments 2 Human Gross Anatomy & Radiology I B. Cricoid cartilage 1. the only cartilage to completely encircle the airway (single piece) 2. has a thin anterior arch and an enlarged lamina posteriorly 3. lamina articulates with the arytenoid cartilages C. Arytenoid cartilages 1. paired set, located posteriorly in the larynx, sitting atop the lamina of the cricoid 2. three-sided pyramidal-shaped cartilages a. posterolateral projection  muscular process b. anterior projection  vocal process (for attachment of the vocal ligament) c. superior apex (articulates with the corniculate cartilages) D. Corniculate cartilages 1. paired, sit atop the apices of the arytenoid cartilages 2. conical-shaped 3. corniculate and cuneiform cartilages are found in the aryepiglottic fold (do not want to mistake for pathological nodules during laryngoscopy). E. Epiglottic cartilage 1. single, paddle or teardrop-shaped cartilage (elastic) 2. located posterior to root of tongue and hyoid bone 3. broad, superior part is free (closes laryngeal inlet) 4. the inferior stalk is attached to the internal surface of the angle between laminae anteriorly 3 Larynx F. Changes with age 1. larynx grows from birth to early childhood 2. at puberty, laryngeal cartilages enlarge and laryngeal prominences become more obvious in males due to influence of testosterone 3. with advanced age, laryngeal cartilages begin to ossify III. Joints A. Cricothyroid joints 1. synovial articulations of inferior horns of thyroid cartilage and the lamina of the cricoid cartilage 2. as thyroid cartilage tilts anteriorly at this joint, the vocal folds are tensed 3. posterior tilting loosens the vocal folds B. Cricoarytenoid joints 1. synovial articulations of arytenoid cartilages and the lamina of cricoid cartilage 2. arytenoid cartilages slide transversely and pivot on cricoid cartilage which results in abduction or adduction of the vocal processes (vocal ligaments attached here) (Acland Video 4.5.3) 3min 20 sec 4 Human Gross Anatomy & Radiology I IV. Ligaments A. Extrinsic ligaments 1. thyrohyoid membrane a. connects superior border of the thyroid cartilage to body and greater horns of the hyoid bone b. thickening of this ligament on midline is median thyrohyoid ligament (single) c. thickening at posterior edges form lateral thyrohyoid ligaments (paired) d. openings allow passage of superior laryngeal vessels and internal laryngeal nerve 2. cricotracheal ligament attaches inferior surface of cricoid c. to upper border of 1st tracheal ring 3. hyoepiglottic ligament a. passes from anterior midline of epiglottis to body of hyoid bone b. limits epiglottic movement to posterior 5 Larynx B. Intrinsic ligaments 1. thyroepiglottic ligament - attaches the stalk of epiglottic cartilage to thyroid cartilage (bottom pic) 2. conus elasticus (with vocal ligament & cricothyroid ligament) a. an elastic membrane that attaches to superior edge of cricoid cartilage and projects superomedially inside the thyroid cartilage to form a partition b. its upper, free edges are thickened to form vocal ligaments (cords) which attach posteriorly to the vocal processes of the arytenoid cartilages and anteriorly to the thyroid laminae c. the thickened anterior portion of conus elasticus is the median cricothyroid ligament and the remaining main part of ligament is the lateral cricothyroid ligament. Lateral cricothyroid ligament 3. quadrangular ligament (membrane) a. this thin submucosal connective tissue, supports the aryepiglottic fold, a mucous membrane b. attached between epiglottic and arytenoid/corniculate cartilages c. its free superior/posterior margin forms the aryepiglottic ligament (aryepiglottic fold) d. its free inferior margin forms the vestibular ligament within vestibular (false vocal) fold e. vestibular ligament attaches to the arytenoid cartilage below its apex and to the thyroid cartilage above the vocal ligament. 6 Human Gross Anatomy & Radiology I V. Interior of larynx with subdivisions A. The larynx is continuous with the pharynx superiorly and the trachea inferiorly and is lined by a mucous membrane, occluding direct view of ligaments and muscles, resulting in folds of tissue. B. The superior opening of the larynx is called the laryngeal inlet (aditus), oriented obliquely between the epiglottis and arytenoid cartilages, along the aryepiglottic folds. The aditus is a aperture, planar. C. The inferior opening is continuous with the trachea bounded entirely by the cricoid cartilage. D. Divisions of the larynx (pictured above) 1. The vestibule (supraglottic space/cavity) is the space between and inferior to the aryepiglottic folds a. above is the laryngeal inlet (aditus) b. below are the vestibular folds (i.e. mucosa covered vestibular ligaments; false vocal cords) c. plane between the vestibular folds is called the rima vestibuli 2. The narrow space between the vestibular and vocal folds is called the laryngeal ventricle.  extends anterosuperiorly as the saccule, a blind pouch with numerous mucous glands 3. The mucosa of the ventricle continues inferiorly to cover the vocal ligaments to form the vocal fold (true vocal cords) 4. The infraglottic space (cavity) is inferior to the vocal folds and superior to the trachea, with mucosa covering the conus elasticus NOTE: The vocal folds are the true vocal cords, which are stretched between vocal processes of arytenoid cartilages and angle of fused thyroid laminae. Vocal folds contain vocal ligament, vocalis muscle, and mucosa covering these structures. The opening between two vocal folds is rima glottidis. The glottis is the vocal apparatus and is formed by vocal folds and rima glottidis. The shape of the rima glottidis varies depending on the activity of the larynx: it is narrow during normal respiration, wide during forced respiration, and slit-like during phonation. (Acland 4.5.4) 2min 31sec 7  Larynx VI. Intrinsic muscles NOTE: Extrinsic muscles of larynx (suprahyoid and infrahyoid muscles) move the entire larynx. Intrinsic muscles of larynx move individual parts of the larynx to fulfill its functions of phonation and to act as the sphincter of the lower respiratory tract. A. Posterior cricoarytenoid muscle 1. arises from lamina of cricoid cartilage 2. inserts superolaterally onto the muscular process of arytenoid cartilage 3. contraction of muscle causes adduction of muscular processes yielding external rotation of arytenoid Abd-Rot cartilages , thus abducting the vocal folds via rotation opening of the rima glottidis (1º abductors) B. Lateral cricoarytenoid muscle 1. arises from the lateral part of the cricoid cartilage (superior to site of cricothyroid muscle) 2. passes posterosuperiorly to attach to the muscular process of arytenoids 3. causes abduction of muscular processes yielding internal rotation of arytenoid cartilages, thus adducting Add-Rot the vocal folds via rotation  closing the rima glottis (1º adductors) C. Transverse arytenoid muscle 1. is a single muscle 2. attaching to each arytenoid cartilage and spanning between the two posteriorly Add-Transl 3. assists with adduction of the vocal folds via translation 8  Human Gross Anatomy & Radiology I D. Oblique arytenoid muscle 1. paired muscles which cross the posterior surface of the transverse arytenoid 2. arise from the muscular processes of arytenoids and cross the midline to attach to the apex of the opposite arytenoid Add-Transl 3. assists in adduction of the vocal folds via translation 4. the oblique arytenoid continues within the aryepiglottic folds forming the aryepiglottic muscle (this muscle, along with adductors above, act collectively as the sphincters for glottis closure) E. Cricothyroid muscle 1. located on external, lateral aspect of larynx 2. arises inferiorly from arch of cricoid cartilage 3. inserts superiorly onto inferior edge of thyroid cartilage, slightly interior 4. contraction of this muscle, acting through cricothyroid joints, causes the thyroid cartilage to Tense-tilt rotate (tilt) anteriorly)  stretches/tenses the vocal folds, raising the pitch of the voice F. Thyroarytenoid muscle 1. found deep to the thyroid laminae 2. arises from anterior part of thyroid cartilage, internally 3. inserts into anterolateral surface of arytenoid cartilages 4. muscle acts through cricoarytenoid joint, pulling the arytenoid cartilages anteriorly, translation Relax-Transl towards the thyroid cartilage, thus relaxing the vocal folds, lowering the pitch of the voice 9 Larynx G. Vocalis muscle 1. sometimes considered a slip of muscle from the thyroarytenoid muscle 2. attaches to anterolateral side of arytenoid cartilage and its vocal process 3. runs parallel to and attaches to the vocal ligament 4. fine tunes the tension on vocal folds and alter timbre of the voice by tensing various segments of the vocal cord (used in whispering) – similar to fingers on the fretboard of a guitar, adjusting strings H. Thyroepiglottic muscle 1. is an extension from thyroarytenoid muscle into aryepiglottic fold 2. acts as sphincter for the aditus, along with aryepiglottic muscle Cricothyroid muscle (Acland 4.5.5) 1min 4sec 10 Human Gross Anatomy & Radiology I VII. Blood supply, venous drainage and lymphatics A. Arterial supply 1. The superior laryngeal artery supplies the upper part of the larynx. Is typically a branch from superior thyroid artery (a branch from the external carotid artery). It passes through opening in the thyrohyoid membrane, in company with superior thyroid vein and internal branch of superior laryngeal nerve. 2. The inferior laryngeal artery is smaller than the superior laryngeal artery. It supplies the lower part of the larynx after arising from inferior thyroid artery (which is a branch from thyrocervical trunk from subclavian artery). It ascends with recurrent laryngeal nerve, passes deep to inferior border of inferior pharyngeal constrictor (cricopharyngeus), and enters larynx by passing deeply near cricothyroid joint. Arterial Lineage ECA – STA – SLA SubclA – TCTrk – ITA - ILA B. Venous drainage generally follows arterial supply. 1. The superior laryngeal vein accompanies the superior laryngeal artery, then typically drains through superior thyroid vein into internal jugular vein. 2. The inferior laryngeal vein drains thru the inferior thyroid vein to the left brachiocephalic vein. C. Lymphatic drainage 1. areas of larynx above vocal cords (supraglottic) follow the superior laryngeal vessels to superior deep cervical lymph nodes 2. infraglottic region of larynx drains to pretracheal or paratracheal lymph nodes and then to inferior deep cervical lymph nodes. 11 Larynx VIII. Innervation A. Sensory is entirely from branches of the vagus. (cell bodies in inferior ganglion of vagus) 1. aditus to the vocal cords, the supraglottic mucosa is supplied by the internal laryngeal nerves (from the superior laryngeal nerves) a. superior is from inferior ganglion of vagus, obliquely medial to carotid arteries along the middle pharyngeal constrictor, then divides into internal & external laryngeal nerves. i. Internal pierces thyrohyoid membrane (with superior laryngeal artery) ii. External descends along the inferior constrictor  innervate cricothyroid (motor) 2. below the vocal cords the infraglottic mucosa is innervated by the recurrent laryngeal nerves. Netter (5th ed.) Plate 80a/b B. Motor 1. the cricothyroid (the only tensor of vocal cords) is innervated by the external laryngeal nerve 2. All other muscles are innervated by the recurrent laryngeal nerves: a. cell bodies in brainstem (vagus origin) b. left recurrent (passes around aortic arch) c. right recurrent (passes around subclavian artery) d. both sides ascend in groove between trachea and esophagus e. both sides pass deep to cricopharyngeus – change names to inferior laryngeal nerve near the cricothyroid joint i. innervates all muscles except cricothyroid 12 Human Gross Anatomy & Radiology I C. Effect of nerve damage to larynx 1. internal laryngeal nerve damage can cause desensitization of superior larynx and hence more likely to have difficulty swallowing yielding laryngeal foreign bodies and choking. 2. external laryngeal nerve damage can paralyze cricothyroid muscle (cannot tense vocal lig., but vocalis can do a little) resulting in a weak voice, lowered pitch and monotone voice. 3. inferior laryngeal nerve damage can result in vocal fold paralysis a. unilateral damage, the other cord can compensate reasonably well (15 second video) b. bilateral damage usually yields no voice and difficult breathing. 4. recurrent laryngeal nerve a. complete division on one side  mid-way abduction (cadaveric position)  minimal impact on voice, as other vocal cord can compensate b. Crushed/bruised results in the sole abductor (posterior cricoarytenoid) being more affected than adductors, which is known as Semon’s law. This yields an adducted position of affected cords.  breathy / bedroom voice. NOTE: Each of these lesions have varying stages, with moments of recovery and synkinesis (involuntary contractions). Semon’s law is a bit obsolete (but is pimping and board relevant), as this is a progressive lesion, starting with abductor being affected 1st, then over time adductors will be affected. Progression discussed in this 15-minute long YouTube video. http://www.youtube.com/watch?v=wjRsa77u6OU http://emedicine.medscape.com/article/863779 13