The Larynx 2023 PDF

THE LARYNX • The larynx (voice box) is an organ located in the anterior neck. • It is a component of the respiratory tract, and has several important functions, including phonation, the cough reflex, and protection of the lower respiratory tract. • The structure of the larynx is primarily cartil...

THE LARYNX • The larynx (voice box) is an organ located in the anterior neck. • It is a component of the respiratory tract, and has several important functions, including phonation, the cough reflex, and protection of the lower respiratory tract. • The structure of the larynx is primarily cartilaginous, and is held together by a series of ligaments and membranes. • Internally, the laryngeal muscles move components of the larynx for phonation and breathing. Anatomical Position and Relations • The larynx is located in the anterior compartment of the neck, suspended from the hyoid bone, and spanning between C3 and C6. • It is continuous inferiorly with the trachea, and opens superiorly into the laryngeal part of the pharynx. • It is covered anteriorly by the infrahyoid muscles, and laterally by the lobes of the thyroid gland. • The larynx is also closely related to the major blood vessels of neck, which pass either side as they ascend up to the head. Infrahyoid mm. Suprahyoid mm. Anatomical Structure • The larynx is formed by a cartilaginous skeleton, which is held together by ligaments and membranes. • The laryngeal muscles act to move the components of the larynx for phonation and breathing. Anatomically, the internal cavity of the larynx can be divided into three sections: • Supraglottis – From the inferior surface of the epiglottis to the vestibular folds (false vocal cords). • Glottis – Contains vocal cords and 1cm below them. • The opening between the vocal cords is known as rima glottidis, the size of which is altered by the muscles of phonation. • Subglottis – From inferior border of the glottis to the inferior border of the cricoid cartilage. • The interior surface of the larynx is lined by a mucous membrane which contains ciliated columnar epithelium. Vasculature The arterial supply to the larynx is via the superior and inferior laryngeal arteries: • Superior laryngeal artery – a branch of the superior thyroid artery (derived from the external carotid). • It follows the internal branch of the superior laryngeal nerve into the larynx. • Inferior laryngeal artery – a branch of the inferior thyroid artery (derived from the thyrocervical trunk). • It follows the recurrent laryngeal nerve into the larynx. • Venous drainage is by the superior and inferior laryngeal veins. • The superior laryngeal vein drains to the internal jugular vein via the superior thyroid, whereas the inferior laryngeal vein drains to the left brachiocephalic vein via the inferior thyroid vein. Innervation • The larynx 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. Unpaired Cartilages; Thyroid Cartilage The three unpaired cartilages are the epiglottis, thyroid and cricoid cartilages. • The thyroid cartilage is a large, prominent structure which is easily visible in adult males. • It is composed of two sheets (laminae), which join together anteriorly to form the laryngeal prominence (Adam’s apple). Thyroid Cartilage • The posterior border of each sheet project superiorly and inferiorly to form the superior and inferior horns (also known as cornu). • The superior horns articulate with the hyoid bone, while the inferior horns are in contact with the cricoid cartilage. Cricoid Cartilage • The cricoid cartilage is a complete ring of hyaline cartilage, consisting of a broad sheet posteriorly and a much narrower arch anteriorly (said to resemble a signet ring in shape). Cricoid Cartilage • The cartilage completely encircles the airway, marking the inferior border of the larynx at the level of C6. • It articulates with the paired arytenoid cartilages posteriorly, as well as providing an attachment for the inferior horns of the thyroid cartilage. Epiglottis • The epiglottis is a leaf shaped plate of elastic cartilage which marks the entrance to the larynx. • Its ‘stalk’ is attached to the back of the anterior aspect of the thyroid cartilage. • During swallowing, the epiglottis moves towards the arytenoid cartilages to close off the larynx and prevent aspiration. Paired Cartilages; Arytenoid Cartilages The arytenoid cartilages are pyramidal shaped structures that sit on the cricoid cartilage. Arytenoid Cartilages • They consist of an apex, base, three sides and two processes, and provides an attachment point for various key structures in the larynx: • 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 • The corniculate cartilages are minor cartilaginous structures. • They articulate with the apices of the arytenoid cartilages. Cuneiform Cartilages • The cuneiform cartilages are located within the aryepiglottic folds. • They have no direct attachment, but act to strengthen the folds. LARYNGEAL MUSCLES • The larynx (voice box) is an organ located in the anterior neck. • It is a component of the respiratory tract, and has several important functions, including phonation, the cough reflex, and protection of the lower respiratory tract. • The muscles of the larynx can be divided into two groups; the external muscles and the internal muscles. • The external muscles act to elevate or depress the larynx during swallowing. • In contrast, the internal muscles act to move the individual components of the larynx – playing a vital role in breathing and phonation. 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). • As a general rule, the suprahyoid muscles and the stylopharyngeus elevate the larynx, whilst the infrahyoid muscles depress the larynx. Intrinsic Muscles • The intrinsic laryngeal muscles act on the individual components of the larynx. • They control the shape of the rima glottidis (opening between the vocal folds and the arytenoid cartilages), and the length and tension of the vocal folds. Intrinsic Muscles • All the intrinsic muscles of the larynx (except the cricothyroid) are innervated by the inferior laryngeal nerve – the terminal branch of the recurrent laryngeal nerve, itself a branch of the vagus nerve. • The cricothyroid is innervated by the external branch of the superior laryngeal nerve – again derived from the vagus nerve. Cricothyroid The cricothyroid muscle stretches and tenses the vocal ligaments, and so is important for the creation of forceful speech. • Attachments: Originates from the anterolateral aspect of the cricoid cartilage, and attaches to the inferior margin and inferior horn of the thyroid cartilage. • Actions: Stretches and tenses the vocal ligament. • Innervation: External laryngeal nerve (branch of superior laryngeal). Thyroarytenoid The thyroarytenoid muscle acts to relax the vocal ligament, allowing for a softer voice. • Attachments: Originates from the inferoposterior aspect of the angle of the thyroid cartilage, and attaches to the anterolateral part of the arytenoid cartilage. • Actions: Relaxes the vocal ligament. • Innervation: Inferior laryngeal nerve (branch of recurrent laryngeal). Posterior cricoarytenoid • The posterior cricoarytenoid muscles are the sole abductors of the vocal folds, and thus the only muscle capable of widening the rima glottidis. • Attachments: Originates from the posterior surface of the cricoid cartilage, and attaches to the muscular process of the arytenoid cartilage. • Actions: Abducts vocal folds. • Innervation: Inferior laryngeal nerve (branch of recurrent laryngeal). Lateral cricoarytenoid • The lateral cricoarytenoid muscles are the major adductors of the vocal folds. • This narrows the rima glottidis, modulating the tone and volume of speech. • Attachments: Originates from the arch of the cricoid cartilage, and attaches to the muscular process of the arytenoid cartilage. • Actions: Adducts the vocal folds. • Innervation: Inferior laryngeal nerve (branch of recurrent laryngeal). Transverse and Oblique Arytenoids • The transverse and oblique arytenoids muscles adduct the arytenoid cartilages, closing the posterior portion of rima glottidis. • This narrows the laryngeal inlet. • Attachments: Spans from one arytenoid cartilage to the opposite arytenoid. • Actions: Adducts the arytenoid cartilages. • Innervation: Inferior laryngeal nerve (branch of recurrent laryngeal). LARYNGEAL LIGAMENTS AND FOLDS • The laryngeal membranes and ligaments support the cartilaginous skeleton of the larynx. • The extrinsic ligaments are situated on the outer aspect of the larynx, while the intrinsic ligaments are located internally. Extrinsic • Thyrohyoid membrane – Spans between the superior aspect of the thyroid cartilage and the hyoid bone. It is 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 (see below), connecting the thyroid and cricoid cartilages. Intrinsic • 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. Intrinsic • 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. Laryngeal Folds • There are two important soft tissue folds located within the larynx – the vestibular folds and vocal folds. • They play an crucial role in protection of the airway, breathing, and phonation. Vocal Folds • The vocal folds (true vocal cords) are the more important of the two sets. • Under the control of the muscles of phonation, they are abducted, adducted, relaxed and tensed to control the pitch of the sound created. Histologically, they are structured as follows (superficial to deep): • Non-keratinised stratified squamous epithelium – Stratified layer provides extensive protection against foreign bodies which may accidentally enter the larynx. • Reinke’s space – This watery, amorphous layer is rich in glycosaminoglycans. • Due to its fluidity, the epithelium is able to vibrate freely above it to create sound. • Vocal ligament – Lies at the free upper edge of the cricothryoid ligament. • Vocalis muscle – Exceptionally fine muscle fibres that lie lateral to the vocal ligaments. • The vocal folds are relatively avascular, and appear white in colour. • The space between the vocal folds is known as the rima glottidis. Vestibular Folds • The vestibular folds (false vocal cords) lie superiorly to the true vocal cords. • They consist of the vestibular ligament (free lower edge of the quadrangular membrane) covered by a mucous membrane, and are pink in colour. • They are fixed folds, which act to provide protection to the larynx.