Gross Anatomy of the Larynx PDF Lecture Notes

Gross Anatomy: Larynx Page 1 of 10 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Describe the anatomy of the larynx including surface anatomy, cartilaginous anatomy, ligam...

Gross Anatomy: Larynx Page 1 of 10 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Describe the anatomy of the larynx including surface anatomy, cartilaginous anatomy, ligaments, membranes, folds, muscles, blood supply, and innervation. 2. Relate the anatomy of the larynx to functions in phonation, respiration, and swallowing. 3. Apply anatomy of the larynx to clinical approaches and problems such as viewing the larynx, laryngeal obstruction, tracheotomy, and CN X lesions. Session Outline I. Anatomy of the Larynx a. Surface Anatomy b. Structural Anatomy of Laryngeal Cartilages c. Ligaments, Membranes, Folds d. Laryngeal Muscles e. Blood Supply f. Innervation II. Functional Effects of Laryngeal Movements a. Phonation b. Respiration c. Valve Mechanism III. Clinical Applications of Laryngeal Anatomy a. Viewing the Larynx b. Laryngeal Obstruction c. Tracheotomy d. CN X Injury Supplemental Reading Gray’s Anatomy for Students, 4th Ed (2020) Drake, Vogl, Mitchell (Elsevier). Ch 8 Scroll to section on Larynx. Gross Anatomy: Larynx Page 2 of 10 Dr. Paul Walker Fig 1 (Grays Anatomy for Students) The larynx is an anatomical valve that allows air to reach the respiratory system while directing food and liquids to the digestive system. It is also provides the phonating mechanism for voice production. The larynx is related in position to the thyroid gland (Fig 1) and is part of the laryngopharynx (Fig 2). I. Anatomy of the Larynx a. Surface Anatomy Spans the position of C3-C6 vertebrae. Fig 2 (Grays Anatomy for Students) Approximately 5 cm long in adult males. Slightly shorter in females & children. The following structures can be palpated (Fig 3): laryngeal prominence cricoid arch cricothryoid ligament thyroid gland Gross Anatomy: Larynx Page 3 of 10 Dr. Paul Walker b. Structural Anatomy of Laryngeal Cartilages Cartilaginous frame- 9 cartilages (3 paired, 3 unpaired) Fibro-elastic membrane with intrinsic muscles (musculoligamentous) Covered with mucosa (same as laryngopharynx) Superior- opens into pharynx. Inferior- continuous with trachea. Attached to hyoid bone above and trachea below Very mobile. Elevated & moved forward during swallowing. Also moves considerably during phonation. Fig 3 (Grays Anatomy for Students) Cartilage Frame (Figs 3-4) Thyroid Cartilage (CV4-CV5 level) Single cartilage made up of two thin plates called thyroid lamina fused anteriorly to form the laryngeal prominence (sharper angle in males). Superior and inferior horns are located posteriorly on each lamina. Inferior pharyngeal constrictor, thyrohyoid & sternothyroid mm. attached to each laminae. The superior horn of each lamina is attached to the hyoid bone by the thyrohyoid membrane. Cricoid Cartilage (CV 6 level) Single cartilage located inferior to the thyroid cartilage. Shaped like a signet ring with the thick part directly posteriorly. Attached to inferior horn of thyroid lamina via special facets (cricothyroid joint) that allow the thyroid cartilage to tilt upon the cricoid cartilage. Cricothyroid ligament provides the fibroelastic connection between thyroid & cricoid cartilages. Arytenoid Cartilages (paired) Located on top of the posterior cricoid cartilage. Shaped like 3-sided pyramids. Base part attached to intrinsic laryngeal muscles and vocal ligaments (not shown). Apex attached to fold (not shown) that helps close the larynx during swallowing. Fig 4 (Grays Anatomy for Students) Gross Anatomy: Larynx Page 4 of 10 Dr. Paul Walker Cartilage Frame (cont’d) Fig 4 repeat (Grays Anatomy for Students) Corniculate & Cuneiform Cartilages (paired) Paired cartilages located on top of the arytenoids (corniculate) or in a laryngeal fold not shown (cuneiform) in Fig 4. Stabilize the structural integrity of the laryngeal folds. Epiglottic Cartilage (single) Thin cartilage shaped like a leaf not labeled in Fig 4. Inferior part is attached to thyroid cartilage via thyroepiglottic ligament. Also attached to the hyoid bone anteriorly via the hyoepiglottic ligament (not shown). helps close the laryngeal inlet during swallowing. c. Ligaments, Membranes, Folds Fig 5 (Grays Anatomy for Students) Cricothyroid Ligament (Fig 5) Extends superiorly from the lateral and anterior parts of the cricoid cartilage. Anterior part called median cricothyroid ligament. Lateral part called lateral cricothyroid ligament. Top edge attached to the vocal ligament. Vocal Ligament (true vocal cord) The elastic vocal ligament extends from the laryngeal prominence (inside) to the vocal processes of the arytenoid cartilages. Cricothyroid ligament + vocal ligament = conus elasticus. Mucosa over the vocal ligament forms the vocal folds. Gross Anatomy: Larynx Page 5 of 10 Dr. Paul Walker Ligaments, Membranes, Folds (cont’d) Quadrangular Membrane Fig 6 (Grays Anatomy for Students) Extends from lateral margin of epiglottis to the ipsilateral arytenoid cartilage (Fig 6). Encloses cuneiform and corniculate cartilages. Its superior edge forms the aryepiglottic fold which is part of the inlet to the larynx. Its inferior edge attaches to the vestibular ligament. Vestibular Ligament (false vocal cord) Extend from thyroid to arytenoid cartilages- parallel but superior to the vocal ligaments (Fig 6). Attached to inferior free edge of the quadrangular membrane. Mucosa over the vestibular ligament forms the vestibular folds. Fig 7 (Grays Anatomy for Students) 3 Compartments of the Larynx (Fig 7): Vestibule: cavity superior to vestibular folds (false vocal cords) up to the aryepiglottic folds. Ventricle: smallest cavity that extends laterally between vestibular folds & superior to vocal folds. Infraglottic: extends from vocal folds to inferior border of cricoid cartilage. Additional Terms Laryngeal aditus- opening into the vestibule bordered by the aryepiglottic fold. Rima glottidis- space between the vocal folds. Gross Anatomy: Larynx Page 6 of 10 Dr. Paul Walker d. Laryngeal Muscles Fig 8 (Grays Anatomy for Students) Cricothyroid muscle (Fig 8) Originates from anterolateral cricoid cartilage and insert on the inferior horn and margin of thyroid cartilage. Thyroarytenoid muscle (Fig 9) Originates from the thyroid angle and inserts into the arytenoid cartilage. Posterior cricoarytenoid muscle (Figs 9-10) Originates from posterior cricoid cartilage and inserts on the muscular processes of the arytenoid cartilages Fig 9 (Grays Anatomy for Students) Lateral cricoarytenoid muscle (Figs 9-10) Originates from lateral surface of cricoid cartilage and inserts on the muscular processes of the arytenoid cartilages. Transverse arytenoid muscle (Figs 9-10) Spans the posterior surfaces of the arytenoid cartilages from one lateral border to the other. Oblique arytenoid muscle (Figs 9-10) Originates from the inferior posterior surface of the arytenoid and inserts into the apex of the contralateral arytenoid. Aryepiglottic muscle (Fig 9) Continuation of oblique arytenoid m. as a muscular slip to insert into the contralateral aryepiglottic fold. Thyroepiglottic muscle (Fig 9) Originates from the thyroid cartilage and inserts on the epiglottic cartilage. Derived from the thyroarytenoid muscle. Vocalis muscle (Fig 10) Originates from vocal process of arytenoid and inserts into the vocal ligament and thyroid angle. Also derived from the thyroarytenoid muscle. Fig 10 (Grays Anatomy for Students) Gross Anatomy: Larynx Page 7 of 10 Dr. Paul Walker e. Blood Supply of Larynx (Fig 11) Fig 11 (Grays Anatomy for Students) Superior laryngeal a. (branch of superior thyroid a.) supplies larynx at or above the level of the vocal folds. Inferior laryngeal a. (branch of inferior thyroid a.) supplies larynx at or below the level of the vocal folds. f. Innervation of Larynx (Fig 12) Fig 12 (Grays Anatomy for Students) The superior laryngeal nerve (CN X) divides into the external laryngeal nerve and the internal laryngeal nerve. The external laryngeal n. provides motor innervation to the cricothyroid m. The internal laryngeal n. pierces the thyrohyoid and provides sensory innervation to the larynx superior to the vocal folds. The recurrent laryngeal nerve provides motor innervation to all intrinsic laryngeal muscles except cricothyroid. The larynx mucosa inferior to the vocal folds is innervated by the sensory fibers within the recurrent laryngeal nerve. The mucosa of the vocal folds are innervated by an overlap of fibers from both internal laryngeal and recurrent laryngeal nerves. Gross Anatomy: Larynx Page 8 of 10 Dr. Paul Walker 2. Functional Effects of Laryngeal Movements a. Phonation (Fig 13) Fig 13 (Grays Anatomy for Students) Cricothyroid m. contraction causes the thyroid cartilage to tilt anteriorly upon the cricoid. This elongates and tightens the vocal ligaments to raise voice pitch. Thyroarytenoid m. contraction shortens the distance between the laryngeal prominence and vocal process of the arytenoids, thus causing the vocal ligaments to slacken which lowers voice pitch. Vocalis m. is part of the thyroarytenoid m. and makes precision adjustments to the tension of the vocal ligaments. Fig 14 (Grays Anatomy for Students) b. Respiration (Fig 14) Lateral cricoarytenoid m. adducts the vocal ligaments by causing internal (medial) rotation of the arytenoid vocal processes. CLOSES rima glottidis. Posterior cricoarytenoid m. abducts the vocal ligaments by causing external (lateral) rotation of the arytenoid vocal processes. OPENS rima glottidis. c. Valve Mechanism (Fig 15) Fig 15 (Grays Anatomy for Students) Arytenoid m. (transverse & oblique) bring the arytenoid cartilages closer to one another to help close the laryngeal aditus. Aryepiglottic m. cinches the aryepiglottic folds together to close the laryngeal aditus. Thyroepiglottic m. approximates the epiglottis to the aryepiglottic folds, which also closes the laryngeal aditus. Gross Anatomy: Larynx Page 9 of 10 Dr. Paul Walker 3. Clinical Application of Laryngeal Anatomy a. Viewing the Larynx Fig 16 (Grays Anatomy for Students) The larynx may be observed with a laryngoscopic mirror or an endoscopic instrument called a laryngoscope. Both vestibular (pink) and vocal (white) folds can be visualized as well as the location of the arytenoid cartilages, aryepiglottic folds, epiglottis, and the trachea (Fig 16). Visualization of the vocal folds and the rima glottidis during normal breathing and phonation is useful to determine the extent of damage to the larynx that may occur as a result of trauma, tumor growth or damage to the recurrent laryngeal nerves during thyroidectomy. b. Laryngeal Obstruction Fig 17 (Grays Anatomy for Students) There is a difference between laryngeal spasm triggered by "food-down-the-wrong-pipe" and a laryngeal obstruction that blocks airflow to the trachea (choking). The former elicits coughing due to touch sensitivity of the laryngeal aditus. However, the person can breathe & may reply "I'm okay" between coughs. Choking occurs when an object becomes lodged in the rima glottidis (Fig 17). This completely blocks air to the trachea and results in unconsciousness. At this point, a Heimlich maneuver must be performed. Choking occurs more commonly at restaurants where alcohol is consumed. Ethanol reduces the sensitivity of the laryngeal aditus. Gross Anatomy: Larynx Page 10 of 10 Dr. Paul Walker c. Cricothyrotomy vs. Tracheotomy Fig 19 (Grays Anatomy for Students) An emergency cricothyrotomy is performed through the median cricothyroid ligament with a tube inserted to provide an air passage to the lungs (Fig 19 right top). This procedure is superior to the thyroid gland isthmus and inferior to the vocal ligaments. However, the proximity of the tube insertion places the vocal ligaments at risk of damage and is a short- term solution to establish an airway. The procedure for a tracheotomy (slit incision in the trachea) or tracheostomy (round or square hole) is no simple task given the structures that lie deep to the incision (Fig 19 right bottom). The most common approach involves a transverse incision at the level of the 2nd- 3rd tracheal rings. The isthmus of the thyroid gland can be palpated through the skin below the cricoid cartilage and is either divided or reflected superiorly. A plexus of inferior thyroid veins is present (Fig 19 left), and sometimes a thyroid ima artery (