The larynx is a flexible passageway for air extending between the oropharynx and the trachea, located below the hyoid bone.

It plays an essential role in sound production and air transmission. The larynx protects the lower airways against food inspiration.

The larynx is mostly built of a cartilaginous skeleton and muscles, and its inner surface is lined with a mucosal membrane.

The part of the larynx above the vocal cords is a part of the upper respiratory tract, while below the vocal cords, it is considered a part of the lower respiratory tract.

Cartilaginous skeleton

The cartilaginous skeleton of the larynx is formed by nine irregularly shaped plates of hyaline and elastic cartilage.

Three large unpaired cartilages are:

And three paired smaller cartilages include:

Arytenoids
Corniculate cartilages
Cuneiform cartilages

The most important two are the epiglottis and arytenoid cartilage.

During swallowing, the pharynx and larynx elevate due to the contraction of the extrinsic laryngeal muscles. The epiglottis moves down and forms a lid over the glottis, closing it off, thereby protecting airways against blockade from food and drinks.

The arytenoid cartilages are able to influence the position and tension of the vocal folds.

Muscles of larynx

The laryngeal muscles are skeletal muscles participating in forming the walls of the larynx and providing movements involved in breathing, phonation, and swallowing processes.

The laryngeal muscles can be divided into two groups:

Extrinsic or external muscles of the larynx - act to elevate or depress the larynx during swallowing;
Intrinsic or internal muscles of the larynx - act to move the individual components of the larynx; these muscles play a vital role in breathing and phonation.

The extrinsic muscles of the larynx move the larynx upwards and downwards. The extrinsic muscles of the larynx include suprahyoid muscle and infrahyoid muscle of the neck and also the stylopharyngeus muscle, a muscle of the pharynx.

The intrinsic muscles of the larynx belong to a group of muscles that activate individual components of the larynx. Overall, they control the shape of the rima glottidis and the length and tension of the vocal cords. The intrinsic laryngeal muscles include the following:

Mucosa of larynx

The mucosa of the larynx forms the inner layer of the laryngeal wall and is continuous with the mucosa of the pharynx above and the trachea below.

The laryngeal mucosa is the chief component of the vestibular folds, where it is the thickest. It is thinner over the vocal folds, where it is firmly fixed to the underlying vocal ligaments. It is loosely attached to the anterior surface of the epiglottis but firmly attached to the anterior surface and the floor of the valleculae.

On the aryepiglottic folds, the mucosa is strengthened by a large amount of fibrous connective tissue, and it attaches closely to the laryngeal surfaces of the cuneiform cartilages and arytenoid cartilages.

Cavity of larynx

The cavity of the larynx extends from the level of the 4th to 5th cervical vertebrae (C4 - C5) to the level of the 6th and 7th cervical vertebrae (C6 - C7). The upper border is marked by the laryngeal opening, also called the laryngeal inlet, while the lower border is formed by the inferior margin of the cricoid cartilage which continues with the trachea.

The cavity of the larynx has three parts:

Vestibule - located between the laryngeal opening and the vestibular folds;
Glottis (vocal apparatus) - between the vestibular folds and vocal folds;
Infraglottic cavity - located between the vocal folds and trachea.

The vestibule is funnel-shaped, and under the mucosa in its side walls is located the quadrangular membrane.

The mucosa of the larynx forms vestibular folds by covering the inferior thickened part of the membrane, it is also called the vestibular ligament.

NOTE: the vestibular folds are also called the false vocal cords, and they do not produce sound as the vocal folds. They only function to protect the vocal folds.

Between the vestibular folds is located the rima vestibuli, while between both vocal folds in the glottis is the rima glottidis.

The most important structures in the vocal apparatus are the vocal folds and rima glottidis. Each fold contains a vocal ligament extending from the thyroid cartilage to the vocal process of the arytenoid cartilage.

Besides the quadrangular membrane, there is one another called the conus elasticus. It extends between the thyroid cartilage, cricoid cartilage and arytenoid cartilages. The mucosa covering the upper portion of the conus elasticus forms the vocal folds.

Both above mentioned membranes are classified as intrinsic membranes and are parts of the fibroelastic membrane of the larynx. The intrinsic membranes connect the laryngeal cartilages.

There are few other membranes in the larynx, but located on the external surface of the larynx and called the extrinsic membranes. They connect the structures of the larynx with adjacent anatomical structures. They are:

Thyrohyoid membrane - extending between the hyoid bone and the thyroid cartilage;
Cricotracheal membrane - connects the cricoid cartilage with the first cartilage of the trachea.

Neurovascular supply

The arterial blood supply to the larynx comes mainly from the superior laryngeal artery (arising from the superior thyroid artery) and inferior laryngeal artery (from the inferior thyroid artery), with rich anastomoses between the corresponding contralateral and between the ipsilateral arteries.

Venous drainage of the larynx is provided by the superior laryngeal vein and inferior laryngeal vein. The first one drains to the superior thyroid vein and next to the internal jugular vein, while the second one drains into the inferior thyroid vein and next to the brachiocephalic vein.

The innervation of the larynx is provided by the vagus nerve (CN X) on each side with its branches - the superior laryngeal nerve and recurrent laryngeal nerve.

The sensory nerve supply to the mucosa of the larynx is provided by two nerves arising from the vagus nerve. The mucosa above the vocal folds are innervated by the internal branch of the superior laryngeal nerve, but below the vocal folds it gets nerve supply from the inferior laryngeal nerve (from the recurrent laryngeal nerve).

The internal laryngeal nerve is the internal branch of the superior laryngeal nerve, arising from the inferior ganglion of the vagus nerve, and it innervates the mucosa of the upper part of the larynx - above the vocal cords. The internal laryngeal nerve divides into three branches. The superior branch supplies the mucosa of the piriform fossa. The middle branch innervates the mucosa of the laryngeal ventricle, specifically the quadrangular membrane, and probably is involved in the cough reflex. The inferior branch mainly supplies the mucosa of the ventricle and subglottic cavity. The nerve also shares many communicating branches with the recurrent laryngeal nerve.

The recurrent laryngeal nerve is a mixed branch of the vagus nerve. It supplies sensory innervation (mainly with its posterior branch) to the mucosa of the larynx below the vocal cords. It also gives branches that anastomose with the internal laryngeal nerve. Thus, at the vocal cords there is an overlap between the territories innervated by the two nerves.

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Larynx