Larynx Anatomy & Function PDF

The Larynx – Overview of Anatomy & Function BSc DTH Case 1.11 Vehid Salih Peninsula Dental School Learning Objectives Identify the anatomy of the larynx and relate how its anatomic location is suited to its function Identify its cartilages, and muscles and their motor innervation an...

The Larynx – Overview of Anatomy & Function BSc DTH Case 1.11 Vehid Salih Peninsula Dental School Learning Objectives Identify the anatomy of the larynx and relate how its anatomic location is suited to its function Identify its cartilages, and muscles and their motor innervation and how they interact to tense or relax the vocal folds during speech To recognise the mucosal lining of the larynx and its sensory innervation The Larynx – what/where is it? Essentially the connection between the pharynx and the trachea Prevents foreign bodies from entering the airways Designed for the production of sound (phonation) Located in the midline opposite the cervical vertebrae (C3 to C6) Formed by 9 cartilages: 6 i.e. 3 paired and 3 unpaired Vallecula is a depression in the mucosa between the pharyngeal portion of the tongue and the anterior border of the epiglottis Larynx – local structures/’surface’ anatomy Hyoid bone – holds up the tongue & larynx Laryngeal prominence (Adam’s Apple) – formed by the angle of the thyroid cartilage surrounding the larynx Cricoid cartilage – maintains airway, provides attachment point for muscles, ligaments & cartilage, all functioning to open/close the vocal chords. Isthmus – connects the lobes of the thymus gland Trachea – extends from the larynx and allows an unobstructed passage of air to & from the lungs Larynx – Functions The larynx functions in swallowing, breathing, and voice production. The production of voice can be thought of in terms of three components: Airflow The generation and resonance of sound (phonation) The articulation of voice Laryngeal inlet Bounded by the epiglottis anteriorly; aryepiglottic folds laterally; interarytenoid tissues posteriorly Leads down to the vestibule of the larynx which extends down to the vestibular folds Principles and management of head and neck cancer Vestibule and Saccule Shane Lester, Woo-Young Yang DOI:https://doi.org/10.1016/j.mpsur.2012.09.002 Between the vestibule and the vocal folds is a small recess, the ventricle of the larynx. This extends upwards to the saccule of the larynx Larynx – membranous folds Two tendinous folds stretched across the larynx from the arytenoid cartilages posteriorly to the thyroid cartilage anteriorly and covered by simple squamous epithelium. The vocal apparatus of the larynx is called the glottis and consists of two vocal folds (true vocal cords) and the rima glottidis (opening between vocal cords). They may contain a few muscle fibres associated with the fine control of speech – the vocalis muscle responsible for adjusting the tension of the vocal folds. Vocal folds are the “true” structures that produce sound as air passes over them, whereas the vestibular folds (false vocal cords) have no role in sound production; they protect the vocal cords. Larynx – Laryngoscopic view Larynx – Membranes & Ligaments (Extrinsic) The extrinsic ligaments act to attach the components of the larynx to external structures (e.g. the hyoid and the cricoid cartilage). Thyrohyoid membrane – Spans between the superior aspect of the thyroid cartilage and the hyoid bone; pierced laterally by the superior laryngeal vessels and internal laryngeal nerve (branch of the superior laryngeal nerve). Median thyrohyoid ligament – Anteromedial thickening of the membrane. Lateral thyrohyoid ligaments – Posterolateral thickenings of the membrane. Hyo-epiglottic ligament – Connects the hyoid bone to the anterior aspect of the epiglottis. Cricotracheal ligament – Connects the cricoid cartilage to the trachea. Median cricothyroid ligament – Anteromedial thickening of the cricothyroid ligament, connecting the thyroid and cricoid cartilages. Larynx – Membranes & Ligaments (Intrinsic) are responsible for holding the cartilages of the larynx together as one functional unit internally Cricothyroid ligament – Originates from the cricoid cartilage and extends superiorly, where it terminates with an free (unattached) upper margin – which forms the vocal ligament. It is additionally attached anteriorly to the thyroid cartilage, and posteriorly to the arytenoid cartilage. Quadrangular membrane – Spans between the anterolateral arytenoid cartilage and the lateral aspect of the epiglottis. It has a free upper margin and lower margin. The lower margin is thickened to become the vestibular ligament. Larynx - Cartilages Unpaired Cartilages Paired Cartilages Thyroid Arytenoid Cricoid Cuneiform Epiglottis Corniculate Total n = 3 Total n = 6 Thyroid Cartilage a large, prominent structure easily visible in adult males. It is composed of two sheets (laminae), which join anteriorly to form the laryngeal prominence (Adam’s apple). posterior border of each sheet project superiorly and inferiorly to form the superior and inferior horns (also known as cornu). superior horns are connected to the hyoid bone via the lateral thyrohyoid ligament, while the inferior horns articulate with the cricoid cartilage. Cricoid & Epiglottis Cartilage is a complete ring of hyaline cartilage, consisting of a broad sheet posteriorly and a much narrower arch anteriorly (signet ring in shape). completely encircles the airway, marking the inferior border of the larynx at C6. It articulates with the paired arytenoid cartilages posteriorly, as well as providing an attachment for the inferior horns of the thyroid cartilage. Epiglottis is a leaf shaped elastic cartilage which marks the entrance to the larynx. It is attached to the back of the anterior aspect of the thyroid cartilage Paired Cartilages Arytenoid Cartilages pyramidal shaped structures that sit on the cricoid cartilage. They consist of an apex, base, three sides and two processes, and provides an attachment point for various key structures : Apex – articulates with the corniculate cartilage. Base – articulates with the superior border of the cricoid cartilage. Vocal process – provides attachment for the vocal ligament. Muscular process – provides attachment for the posterior and lateral cricoarytenoid muscles. Corniculate Cartilages minor cartilaginous structures; articulate with the apices of the arytenoid cartilages. Cuneiform Cartilages located within the aryepiglottic folds; act to strengthen the folds. Larynx – Movements & Musculature Movements of the Larynx These include …. − Movements during respiration − Movements during phonation − Movements that protect the laryngeal airway during swallowing Extrinsic Muscles of the Larynx These move the larynx in its entirety and include the …. − Suprahyoid muscles − Infrahyoid muscles Intrinsic Muscles of the Larynx These alter …. − the length and tension of the vocal folds − the size and shape of the ‘rima glottidis’ Larynx - Muscles Extrinsic Muscles The extrinsic muscles act to move the larynx superiorly and inferiorly. They are comprised of the suprahyoid and infrahyoid groups, and the stylopharyngeus (a muscle of the pharynx). Extrinsic muscles Infrahyoid muscles: sternohyoid muscle, omohyoid muscle, sternothyroid muscle, thyrohyoid muscle Suprahyoid muscles: stylohyoid muscle, digastric muscle, mylohyoid muscle, geniohyoid muscle The supra- and infrahyoid muscle groups attach to the hyoid bone. This, in turn, is bound to the larynx by strong ligaments; allowing the whole of the larynx to be moved as one unit. As a general rule, the suprahyoid muscles and the stylopharyngeus elevate the larynx, whilst the infrahyoid muscles depress the larynx.  Intrinsic Muscles Vocalis – proximal attachment of the vocalis muscle is on the vocal process of the arytenoid cartilage. It inserts distally upon the vocal ligament and acts by tensing the anterior vocal ligament and relaxing the posterior vocal ligament i.e. it makes small adjustments to the tension of the vocal ligaments. Muscle movement during phonation The larynx produces column of air vibrating at an audible frequency. This leads to sound which becomes modified during its passage through the upper airway. Air is forced past vocal folds that are closed to form a slit like glottis. The arytenoids are medially rotated and are adducted by contraction of the lateral cricoarytenoid muscles The pitch of a sound reflects the tension or length of the vocal folds Low pitched sounds are produced when the folds are relaxed, high pitched sounds when they are taut. Puberty; expansion of the larynx and elongation of the vocal folds – the voice breaks Larynx - Mucosae The mucosa of the lingual surface of the epiglottis (as well as half of the laryngeal surface) is continuous with that of the laryngopharynx. It is lined with stratified squamous non keratinized epithelium (lingual mucosa); the other half of its laryngeal surface is lined by pseudostratified ciliated columnar epithelium. Deep within the lamina propria of the mucosa are seromucous glands. The top of the trachea then comprises columnar pseudostratified with cilia and goblet cells. Larynx - Innervation receives both motor and sensory innervation via branches of the vagus nerve: Recurrent laryngeal nerve – provides sensory innervation to the infraglottis, and motor innervation to all the internal muscles of larynx (except the cricothyroid). Superior laryngeal nerve – the internal branch provides sensory innervation to the supraglottis, and the external branch provides motor innervation to the cricothyroid muscle. Larynx - Blood Supply The arterial supply of the larynx is by the superior and inferior laryngeal arteries which are branches of the thyroid arteries. The larynx is drained by corresponding veins, namely the superior and inferior laryngeal veins. SDL https://www.youtube.com/watch?v=tfXCdRhxxdk https://www.youtube.com/watch?v=xAtiJTLBvlI https://www.youtube.com/watch?v=b89RSYCaUBo https://www.kenhub.com/en/library/anatomy/larynx https://teachmeanatomy.info/neck/viscera/larynx/