Larynx

• Relations

  The first diagram shows the larynx as seen from the anterior triangle of the neck, as it lies under the strap muscles. Some of these muscles will connect to the larynx . When these muscles are reflected, the thyroid gland can be seen sitting either side of the trachea. the thyroid gland majority sits inferior to the larynx as a whole. The final diagram shows a view of the posterior part of the larynx as viewed from inside the laryngopharynx. It is covered by mucous lining,

  
• Larynx

  The larynx is involved in phonation and therefore contributes to producing speech. The main supporting parts of the larynx are composed of pieces of hyaline cartilage which articulate with each other via tiny plane synovial joints. This allows the individual cartilages to perform small sliding and gliding movements to allow movements between the thyroid and cricoid cartilages and between the arytenoid cartilages and the cricoid cartilage.

  
• Thyroid cartilage

  The thyroid cartilage is the largest cartilage of the larynx and forms the laryngeal prominence. It is attached to the hyoid bone via the thyrohyoid membrane, which ensures that muscles which elevate the hyoid bone also elevate the larynx. The thyroid cartilage articulates with the cricoid cartilage inferiorly and provides attachment for 2 muscles of the anterior triangle in addition to the inferior constrictor of the pharynx.

  
• Cricoid cartilage

  The cricoid cartilage forms a signet ring shape, with the thin band of the ring anterior and the signet gemstone part facing posteriorly. It articulates with the thyroid and arytenoid cartilages. It also provides an area of attachment for several intrinsic muscles of the larynx – for example posterior cricoarytenoid. The trachea sits inferior to the cricoid cartilage and is attached to it by a thickened membrane – the cricotracheal ligament.

  
• Arytenoid cartilages

  The arytenoid cartilages articulate with the cricoid cartilage and swivel on the surface of the cricoid to move the vocal folds. There are 2 arytenoid cartilages, each one has a muscular process for the attachment of the posterior and lateral cricothyroid muscles which act to move the vocal folds. Each arytenoid cartilage also has a vocal process that provides attachment for the vocal folds.

  
• Corniculate, cuneiform and epiglottis

  The corniculate and cuneiform cartilages are tiny pieces of cartilage that attach to and support the aryepiglottic folds between the arytenoid cartilages and the epiglottis.

  
• Epiglottis

  •Elastic cartilage

  •Anterior connections to body of hyoid bone and posterior surface of thyroid cartilage

  •Lateral connections to arytenoid cartilages via aryepiglottic folds

  •Mucous membrane covering reflected onto posterior surface of tongue – median glossoepiglottic fold and lateral pharyngoepiglottic folds

  
• Membranes and ligaments

  •Arytenoid cartilages to epiglottis = quadrangular ligament – free edge is vestibular ligament (false vocal fold)

  •Cricoid, thyroid and arytenoid = cricothyroid membrane – free upper border is the vocal ligament

  
• Membranes and ligaments

  The quadrangular ligament passes between the arytenoid cartilages and the epiglottis. Close to the arytenoid cartilages it folds over itself to form a thickened free edge. This is also called the false or vestibular vocal fold.  The true vocal fold is formed from a membrane passing between the cricoid, thyroid and arytenoid cartilages. The upper border of this membrane folds to form a free edge called the vocal ligament (this is the vocal cord).

  
• Membranes

  The lower free edge of the quadrangular ligament forms the false vocal fold. The upper border of the quadrangular ligament is called the aryepiglottic fold.

  
• Vocal folds

  The vestibular (false) fold protects the true vocal fold beneath it. The true vocal folds are moved in and out (adduction and abduction) to disrupt the flow of air through the larynx. This movement combined with the tension in the vocal folds creates sound.

  the rima glottidis – the most posterior space between the vocal folds.

  
• Vocal folds

  sagittal cross-section of the head, you can see the vestibular fold most superior and the true vocal fold inferior.

  
• Vocal fold movements

  •Change air flow through larynx = sound production (phonation). Individual sounds/words created by movements of lips, cheeks and tongue.

  
• Muscles

  •External (extrinsic) = supra and infra-hyoid muscles of the neck which attach to the hyoid bone or thyroid cartilage and move the entire larynx – swallowing

  •Elevation = digastric, stylohyoid, mylohyoid, geniohyoid (stylopharyngeus, salpingopharyngeus, palatopharyngeus)

  •Depression = sternothyroid, sternohyoid, omohyoid (elastic recoil of trachea)

  •Internal (intrinsic) = muscles which pass between elements of the larynx and move the cartilages or vocal folds
• Cricothyroid

  •Cricoid cartilage to lamina and inferior cornu of thyroid cartilage

  •Tense and elongate vocal folds (increase distance between thyroid cartilage and vocal processes of arytenoid = thyroid forward and cricoid tilted backwards)

  •External laryngeal branch of vagus (CN X)

  It sits on the anterior surface of the larynx

  
• Cricothyroid

  Cricothyroid tilts the two large laryngeal cartilages in relation to each other. As the vocal fold attaches to the thyroid and arytenoid cartilages this also changes the relative position of the two ends of the vocal fold. As the cartilages tilt, the vocal fold is stretched which increases the tension in the fold. This will change the pitch of any sound created.

  
• Thyroarytenoid

  •Inner surface of angle of thyroid cartilage to the anterolateral surface of the arytenoid cartilages

  •Upper fibres run alongside vocal ligament = and are called vocalis

  •Pull arytenoids forwards towards thyroid cartilage = shorten and relax vocal ligament

  •Recurrent laryngeal nerve (vagus CN X)

  it pulls the arytenoid cartilages closer to the thyroid cartilage. So, it has the opposite effect – it makes the folds shorter and less tense – changing the pitch of any sound produced.

  
• Posterior cricoarytenoid

  •Posterior of lamina of cricoid cartilage to muscular process of arytenoid cartilage

  •Pulls muscular process of arytenoid backwards – rotating vocal process laterally = abduction of vocal fold

  •Recurrent laryngeal branch of vagus (CN X)

  It passes between the cricoid cartilage and the muscular processes of the arytenoid cartilages

  
• Lateral cricoarytenoid

  •Upper edge of arch of cricoid cartilage to muscular process of arytenoid cartilages

  •Pulls muscular process forwards – rotate vocal process medially = adduction of vocal fold

  •Recurrent laryngeal branch of vagus (CN X)

  
• Oblique arytenoid

  •Muscular process of arytenoid cartilage to apex of opposite arytenoid cartilage

  •Some fibres form aryepiglottic muscles in aryepiglottic fold

  •Sphincter of laryngeal inlet

  •Recurrent laryngeal branch of vagus (CN X)

  It also brings the edges of the quadrangular membrane closer together (and therefore the aryepiglottic folds).

  
• Transverse arytenoid

  •Posterior and medial surfaces of arytenoid cartilages to opposite arytenoid cartilage

  •Closes posterior part of rima glottidis

  •Recurrent laryngeal branch of vagus (CN X)

  
• Oblique arytenoid and transverse arytenoid can help to protect the true vocal fold by physically moving the aryepiglottic folds into the pathway of any food debris or fluid before it reaches the vocal folds, and by narrowing the inlet and the gap between the folds can help prevent fluid aspiration further into the larynx and trachea.

  
• Vagus nerve (CN X)

  The vagus nerve supplies the intrinsic muscles of the larynx. The external laryngeal nerve supplies cricothyroid. It is a branch of the superior laryngeal nerve which also carries sensory fibres to the inner surface of the larynx via the internal laryngeal branch of the vagus nerve. The majority of the intrinsic muscles are supplied by the recurrent laryngeal nerve.

  
• Vagus nerve (CN X)

  This branches from the main vagus nerve in the thorax and passes around either the subclavian artery on the right side (as shown in diagram) or around the arch of the aorta on the left side. It then ascends the neck lying between the trachea and oesophagus, before it passes under the inferior constrictor of the pharynx to reach the larynx.

  
• Arteries

  The arteries that supply the larynx originate from the thyroid arteries, which in turn originate from the external carotid (superior) and subclavian arteries (inferior).

  
• Veins

  The veins follow a similar pathway, draining into the superior and inferior thyroid veins. The superior veins drain into the internal jugular vein on both sides, and both of the inferior veins drain into the left brachiocephalic vein.

  
• Lymphatics

  The lymph drainage of the larynx is to local paratracheal nodes and to the deep cervical nodes.