Michael aritonang, M.D.Dept of AnesthesiologyManila Adventist Medical CenterAnatomy of the Larynx

OutlineDescriptionLaryngeal OssiclesIntrinsic MusclesVasculatureInnervationPhonation

What is the larynx?It is a compound sphincterCloses the airway during swallowingCloses the airway during the Valsalva manuever (coughing, urination and defecation)It constricts the airway during phonation

DifferencesAdultsC4-C6Narrowest portion is the Cricoid

Infant/ChildC3-C5Narrowest portion is the Vocal folds

More differences in infants/childrenEpiglottis is longer, narrower and stifferAryepiglottic folds closer to midline in infantsVocal folds anterior angle with respect to perpendicular axis of the larynxPliable cartilageMucosa more vulnerable to trauma

The Laryngeal OssiclesHyoid bone3 unpaired ThyroidCricoidEpiglottis3 paired ArytenoidCorniculateCuneiform

Hyoid bone U-shapedPartsBodyLesser hornsGreater horns

Hyoid bone Body Hyoglossus mylohyoidmiddle constrictor Medial surface attachment of thyrohyoid membrane

Epiglottis

Epiglottis

EpiglottisFunction - during the pharyngeal of deglutition, elevation of the hyoid bone draws the attached larynx cranially so the epiglottis assumes a more horizontal position thus protecting the glottic opening.

EpiglottisSensation from the upper epiglottic surface is carried by the glossopharyngeal nerve which provides the afferent limb of the gag reflex

EpiglottisSensation from the lower surface carried by the internal branch of the superior laryngeal branch of the vagus nerve, afferent limb of the cough reflex

EpiglottisEpiglottic taste buds innervated by the internal branch of the superior laryngeal nerve

QuestionWhen inserting a mac blade during laryngoscopy, which nerve on the epiglottis do you stimulate?

Thyroid Cartilage Median thyroid notchLaryngeal prominenceInferior horns articulates with the cricoid cartilage at the cricothyroid joint

Cricoid CartilageFrom the greek word krikosBroad posterior lamina and narrow anterior arch

Cricothyroid Membrane9mm in height and 3 cm in width1-1.5 finger breadths below laryngeal prominenceIn upper third, crossed by anastomosis of the left and right superior cricothyroid arteries

QuestionWith regards to incisions or needle puncture to the cricothyroid membrane, where should the incision be made and in what direction?

Arytenoid CartilagesThe base forms a shallow ball and socket articulation with the upper border of the cricoid laminaThe apex is surmounted by the small nonfunctional corniculate cartilage

Arytenoid CartilagesThe muscular process receives the posterior and lateral cricoarytenoid muscles and transverse arytenoid muscleThe vocal process receives the vocal ligament

Intrinsic Muscles

CricothyroidTenses vocal chordsSuperior laryngealPosterior CricoarytenoidAbducts vocal chordsInferior laryngealLateral CricoarytenoidAdducts vocal chordsInferior laryngealTransverse arytenoidAdducts vocal chordsInferior laryngeal

Intrinsic Muscles

Oblique arytenoidConstricts rima glottidisInferior laryngealThyroarytenoidAdducts and relaxes vocal chordsInferior laryngealVocalis portion of thyroarytenoidTenses vocal folds to raise pitchInferior laryngeal

VasculatureSuperior laryngeal branch of the superior thyroid artery from the external carotid arteryInferior thyroid artery from the thyrocervical trunk

InnervationBy branches of the vagusSuperior laryngeal nerveInferior (Recurrent) laryngeal nerve

Superior Laryngeal NerveInternal branch pierces the thyroid membrane and is sensory onlyAfferent limb of cough reflexExternal branchInnervates the cricothyroid muscle

Inferior (recurrent) laryngeal nerveConveys sensation to the laryngeal and tracheal mucosa below the vocal foldsProvides innervation to the intrinsic muscles except the cricothyroid

Inferior (recurrent) laryngeal nerveIn the lower neck, it ascends between the esophagus and tracheaIn the middle of the neck, it runs behind the posterior surface of the thyroid gland

Inferior (recurrent) laryngeal nerveOn the right, it passes around the subclavian arteryOn the left, it passes below the ligamentum arteriosum

PhonationAccomplished by adducting the vocal chords sufficiently to vibrate in the exhaled air (lateral cricoarytenoid and transverse arytenoid)Tensing the chords strengthens vibrations and raises the pitch

PhonationShortening the cords raises the pitch (vocalis)Vibrations are transmitted in the pharyngeal, oral, nasal passages and paranasal sinuses producing resonance

ArticulationAccomplished by varying the resonance characteristics of the nasopharynx, oropharynx and oral cavity to produce vowel sounds. Interrupting the resonance produces consonant sounds

Effects of laryngeal nerve injury

Superior laryngeal nerveUnilateralBilateralMinimal EffectsHoarseness, tiring of voiceRecurrent laryngeal nerveUnilateralBilateral Acute ChronicHoarseness

Stridor, respiratory distressAphoniaVagus NerveUnilateralBilateralHoarsenessAphonia

QuestionHow will the glottic opening look like when one has a bilateral vagal nerve transection?

*****************************************