Anatomy and Functions of the Larynx

Larynx Structure and Function

• The larynx, or voice box, is located in the anterior neck and is a component of the respiratory tract.
• It has three main functions: phonation, the cough reflex, and protection of the lower respiratory tract.
• The larynx is primarily cartilaginous, held together by ligaments and membranes.
• 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 spans between C3 and C6.
• It is continuous inferiorly with the trachea and opens superiorly into the laryngeal part of the pharynx.
• The larynx is covered anteriorly by the infrahyoid muscles and laterally by the lobes of the thyroid gland.
• It is closely related to the major blood vessels of the neck, which pass either side as they ascend up to the head.

Internal Cavity

• The internal cavity of the larynx can be divided into three sections: supraglottis, glottis, and subglottis.
• The supraglottis extends from the inferior surface of the epiglottis to the vestibular folds (false vocal cords).
• The glottis contains the vocal cords and is 1cm below them.
• The subglottis extends from the inferior border of the glottis to the inferior border of the cricoid cartilage.

Vasculature

• The arterial supply to the larynx is via the superior and inferior laryngeal arteries.
• The superior laryngeal artery is a branch of the superior thyroid artery and follows the internal branch of the superior laryngeal nerve into the larynx.
• The inferior laryngeal artery is a branch of the inferior thyroid artery and follows the recurrent laryngeal nerve into the larynx.
• Venous drainage is by the superior and inferior laryngeal veins.

Innervation

• The larynx receives both motor and sensory innervation via branches of the vagus nerve.
• The recurrent laryngeal nerve provides sensory innervation to the infraglottis and motor innervation to all the internal muscles of the larynx (except the cricothyroid).
• The superior laryngeal nerve provides sensory innervation to the supraglottis and motor innervation to the cricothyroid muscle.

Cartilages

• The larynx has three unpaired cartilages: the epiglottis, thyroid cartilage, and cricoid cartilage.
• The thyroid cartilage is a large, prominent structure that is easily visible in adult males.
• It is composed of two sheets (laminae) that join together anteriorly to form the laryngeal prominence (Adam's apple).
• The cricoid cartilage is a complete ring of hyaline cartilage that encircles the airway.
• The epiglottis is a leaf-shaped plate of elastic cartilage that marks the entrance to the larynx.

Paired Cartilages

• The arytenoid cartilages are pyramidal shaped structures that sit on the cricoid cartilage.
• They consist of an apex, base, three sides, and two processes.
• The corniculate cartilages are minor cartilaginous structures that articulate with the apices of the arytenoid cartilages.
• The cuneiform cartilages are located within the aryepiglottic folds and have no direct attachment.

Laryngeal Muscles

• The laryngeal muscles can be divided into two groups: extrinsic and intrinsic muscles.
• The extrinsic muscles act to move the larynx superiorly and inferiorly during swallowing.
• The intrinsic muscles act to move the individual components of the larynx, playing a vital role in breathing and phonation.
• The cricothyroid muscle stretches and tenses the vocal ligaments, and is important for the creation of forceful speech.
• The thyroarytenoid muscle acts to relax the vocal ligament, allowing for a softer voice.