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TSM32: LARYNX 15/10/08 LEARNING OUTCOMES Describe the functional anatomy of the larynx The larynx joins the upper and lower respiratory tracts – from the pharynx to the trachea o Comprises muscle, ligament and cartilage suspended from the hyoid bone o Lined internally by mucosa forming a tubular passage for air o Acts as a valve to protect the lower respiratory tract and produces sounds o Sensory and motor supply all through branches of the vagus nerve (CNX) There are three regions of the larynx divided by two pairs of folds in the mucosal lining: o Vestibule – between the laryngeal inlet and the vestibular folds (of the vestibular ligament) o Middle – thin area between the vestibular and vocal folds (with bilateral ventricles) o Infraglottic space – between the vocal folds (of the vocal ligament) and trachea LARYNGEAL CARTILAGES There are three main unpaired cartilages forming the bulk of the laryngeal framework: o Cricoid – shaped like a ‘signet ring’ with a broad posterior lamina and thin anterior arch Caps the trachea Articulates with the arytenoid cartilages superiorly Articulates with the thyroid cartilage postero-laterally o Thyroid – largest cartilage, U-shaped, closed anteriorly but open posteriorly Covers the bulk of the larynx and forms the anterior laryngeal wall Anterior laryngeal prominence in the midline (Adam’s apple) Articulates with the cricoid via small infero-posterior projections – inferior horns Articulates with the hyoid bone superiorly via lateral thyroid ligaments from the superior horns o Epiglottis – leaf-shaped flap that can occlude or expose the laryngeal inlet Attached at its ‘stem’ to the lower internal surface of the anterior thyroid cartilage Suspended from the hyoid bone in the midline by the hyoepiglottic ligament Projects postero-superiorly towards the pharyngeal tongue There are also three sets of smaller paired cartilages: o Arytenoids – pyramid-shaped with posterior, antero-lateral and medial surfaces Concave bases articulate inferiorly with the posterior cricoid cartilage Articulate superiorly (at the apices) with the corniculate cartilages Antero-lateral surfaces attach to the vocalis muscle and vestibular ligament Anterior vocal processes attach to the vocal ligaments Lateral muscular processes attach to the crico-arytenoid muscles o Corniculates – small, conical Articulate at the base inferiorly to the apex of the arytenoid cartilage Apices project posterior-medially o Cuneiforms – small, club-shaped Suspended in the laryngeal membrane between the corniculates and the epiglottis LARYNGEAL MEMBRANE The larynx is supported structurally by an internal fibroelastic membrane comprising two parts: o Cricothyroid ligament – inferiorly Extends round the arch of the cricoid cartilage Attaches at a point anteriorly to the internal surface of the thyroid cartilage Attaches bilaterally posteriorly to the vocal processes of the arytenoid cartilages Thickened free superior margin between these points forms the vocal ligament o Quadrangular membrane – superiorly Extends round the lateral borders of the epiglottis Attaches at a point anteriorly above the attachment of the cricothyroid ligament Attaches bilaterally posteriorly to the antero-lateral surfaces of the arytenoids Thickened free inferior margin between these points forms the vestibular ligament There are two distinct openings between the mucosal folds visible from above in laryngoscopy: o Rima vestibuli – between the two vestibular folds (‘false’ vocal cords) o Rima glottidis – between the two vocal folds (‘true’ vocal cords) LARYNGEAL MUSCLES AND INNERVATION The larynx houses several intrinsic muscles which control various intrinsic movements: o Cricothyroid – pulls the thyroid cartilage down onto the cricoid; lengthens vocal ligaments o Posterior crico-arytenoid – externally rotates the arytenoid cartilages; opens vocal ligaments o Lateral crico-arytenoid – internally rotates the arytenoid cartilages; closes vocal ligaments o Vocalis – follows the vocal ligaments; adjusts tension in vocal ligaments The recurrent laryngeal nerve (branch of vagus) provides: o Motor innervation to all the above muscles except cricothyroid o Sensory innervation below the vocal folds The superior laryngeal nerve (branch of vagus) provides: o Motor innervation to cricothyroid only o Sensory innervation above the vocal folds