THE LARYNX

The LarynxThe larynx connects the inferior pharynx to the trachea. It serves as a valve to guard air passage, maintains a patent airway and functions in vocalization. The larynx is about 5 cm in length and comprises several cartilages, muscles and membranes.

Cartilages Thyroid a single cartilage formed by two laminae fused in the midline which produces a laryngeal prominence (Adam's apple).

Cricoid a single cartilage located below the thyroid cartilage and between the latter and the first tracheal cartilage.

Epiglottic a single cartilage located behind root of tongue and anterior to inlet of larynx - guards the vestibule of the larynx during swallowing.

Paired Cartilages arytenoid, corniculate and cuneiform which function in vocalization and control of passageway (rima glottidis) between vocal cords.Laryngeal Inlet or Aditus

The inlet of the larynx faces posteriorly and connects the laryngopharynx to the cavity of the larynx, specifically the vestibule. The inlet is guarded by the epiglottis and a muscular sphincter (aryepiglottic muscles).

Cavity

The cavity of the larynx is divided into three regions by the vestibular folds (false vocal cords) and vocal folds (true vocal cords).

Vestibule from the inlet to the vestibular folds.

Ventricles between the vestibular folds and the vocal folds. Infraglottic Cavity from the vocal folds to the trachea.

Membranes and Ligaments Thyrohyoid Membrane Connects the hyoid to the thyroid cartilage the membrane presents an opening in each side for passage of the internal laryngeal nerves and the superior thyroid vessels this membrane guarantees that when the hyoid is elevated so is the larynx and when the larynx is depressed so is the hyoid.

Cricothyroid Ligament Connects the cricoid cartilage to the thyroid cartilage. Cricotracheal Ligament - connects cricoid cartilage to first tracheal ring. Vocal Ligament An elastic ligament which passes from the thyroid cartilage in front to the arytenoid cartilage in the back covered by a fold of mucosa forming the vocal fold.

Vestibular Ligament A poorly defined band of connective tissue passing from the thyroid cartilage in front to the arytenoid cartilage in back covered by loose layer of mucosa forming the vestibular fold.

Muscles

Extrinsic these move the larynx as a whole.

Elevators thyrohyoid, stylohyoid, mylohyoid, digastric, stylopharyngeus and palatopharyngeus muscles.

Depressors omohyoid, sternothyroid and sternohyoid muscles.

Intrinsic only move parts of larynx itself - includes the muscles concerned with sound production, closure of the inlet and closure of the rima glottidis - innervated by vagus nerve via the inferior laryngeal branches of the recurrent laryngeal nerves except for cricothyroid which is innervated by external laryngeal nerve.

The Air Passageway through the Larynx

The passageway for air through the larynx is controlled at three different levels.

At the Inlet by the aryepiglottic muscles in the aryepiglottic folds, the muscles adduct the folds.

Between the Vestibular Folds closes when one desires to increase intrathoracic and intraabdominal pressure. At the Rima Glottidis (between the vocal folds) narrows during speaking - (the glottis comprises the vocal folds, processes and the rima glottidi.

Vascularization of the Larynx

arteries of the larynx

ArteryOriginCourseDistribution

Superior Laryngeal A.superior thyroid artery - a branch of the external carotid arterypasses with the internal laryngeal nerve through a hiatus in the thyrohyoid membrane supplies muscles and mucous membranes of the larynx - anastomoses with the laryngeal thyroid artery

Inferior laryngeal A.inferior thyroid artery - a branch of the thyrocervical trunk ascends on the trachea with the recurrent laryngeal nerve - enters the larynx at the inferior border of the inferior constrictor supplies muscles and mucous membranes of the larynx - anastomoses with superior laryngeal artery

Innervation of the Larynx

nerves of the larynx

NerveOriginCourseDistribution

External Laryngeal superior laryngeal nerve - a branch of the vagus nerve

(CN X)

descends deep to the sternothyroid to reach the inferior constrictor and cricothyroidmotor fibers to cricothyroid and inferior constrictor of pharynx

Internal Laryngeal passes with the superior laryngeal artery through a hiatus in the thyrohyoid membranesensory to laryngeal mucosa down to the level of the vocal folds - also conveys afferents from laryngeal muscles and stretch receptors

nerves of the larynx (cont.)

NerveOriginCourseDistribution

Recurrent Laryngeal Nervevagus nerve

(CN X)right side: recurves around subclavian artery- ascends on the side of the trachea behind the common carotid artery

left side: recurves around the aortic arch just behind the ligamentum arteriosum and ascends to the side of the trachea

both: ascend in groove between trachea and esophagus to enter larynx deep to inferior border of inferior constrictor motor to all intrinsic muscles of larynx except cricothyroid, sensory to mucus membranes up to the vocal folds - afferents from stretch receptors

Clinical Note: The cricothyroid ligament is the structure that is pierced in an emergency to open the airway when done by a nonsurgeon. This procedure is called a cricothyrotomy. When a surgeon does a tracheotomy he or she slices an opening through the second and third tracheal rings ( this varies) to insert a tracheotomy tube. In a tracheostomy the tracheal mucosa is brought into continuity with the skin; the tracheostomy is for long term situations.

Clinical Note: Damage to the recurrent laryngeal nerves (or to the vagus nerves can result in flaccid paralysis of the vocalis muscles and collapse of the rima glottidis and possible suffocation. Since the left recurrent laryngeal nerve wraps around the aortic arch, aneurysms in the arch can put pressure on the nerve and result in loss of tone in the left vocalis muscle and a slackness in the left vocal cord producing an otherwise unexplained hoarseness.

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