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TSM32: LARYNX
15/10/08
LEARNING OUTCOMES
Describe the functional anatomy of the larynx
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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
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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
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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
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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