Human Anatomy and Physiology - N. I. Fedyukovich 2003

Internal Organs
Respiratory System
Larynx

The Larynx serves the Functions of Respiration, phonation, and Protection of the lower Airways from foreign particles. It is located in the anterior region of the neck, at the level of the IV–VII cervical vertebrae; On the surface of the neck, it forms a prominence (the laryngeal prominence, or Adam's apple) that is small in women and highly protruding in men. Superiorly, the larynx is suspended from the Hyoid bone, and inferiorly, it connects to the Trachea. Anterior to the larynx lie the Muscles of the neck, while neurovascular bundles are situated laterally.

The laryngeal Skeleton consists of unpaired and paired cartilages. The unpaired cartilages include the thyroid, cricoid, and epiglottis, while the paired ones comprise the arytenoid, corniculate, and cuneiform cartilages, which are interconnected by ligaments, Connective Tissue membranes, and joints.

Cartilages of the larynx. The foundation of the larynx is the hyaline cricoid Cartilage, which connects to the first tracheal cartilage via a ligament. It consists of an arch and a quadrangular lamina; the arch of the cartilage faces anteriorly, while the lamina faces posteriorly. On the superior border of the lamina, There are two articular facets for articulation with the arytenoid cartilages. Situated above the cricoid cartilage is the unpaired hyaline thyroid cartilage, which is the largest cartilage of the larynx. On the anterior aspect of the thyroid cartilage, there are the superior thyroid notch and a small inferior thyroid notch. The posterior borders of the thyroid laminae project on each side as a long superior horn and a short inferior horn. The arytenoid cartilage is paired, hyaline, and resembles a three-sided pyramid. It has anterolateral, medial, and posterior surfaces. The Base of the cartilage is directed inferiorly, and the apex is pointed and slightly curved posteriorly. Extending from the base is the muscular process, and the vocal process, to which the vocal ligament and Muscle attach. From above and anteriorly, the laryngeal inlet is covered by the epiglottis, an elastic cartilaginous plate. It is attached to the thyroid cartilage by the thyroepiglottic ligament. The epiglottis seals the laryngeal inlet during swallowing. The corniculate and cuneiform cartilages are located within the aryepiglottic folds.

The cartilages of the larynx are articulated with each other and with the hyoid bone by means of joints (cricothyroid, cricoarytenoid) and ligaments (thyrohyoid membrane, median thyrohyoid, lateral thyrohyoid, hyoepiglottic, thyroepiglottic, cricothyroid, cricotracheal).

Muscles of the larynx. All laryngeal muscles are divided into three groups: dilators, constrictors of the rima glottidis, and those that alter the tension of the vocal cords.

The only muscle that dilates the rima glottidis is the posterior cricoarytenoid muscle. Upon contraction, this paired muscle pulls the muscular process posteriorly, rotating the arytenoid cartilage laterally. The vocal process also rotates laterally, thereby widening the rima glottidis.

The group of muscles that constrict the rima glottidis includes the paired lateral cricoarytenoid and paired thyroarytenoid muscles, the paired oblique arytenoid muscles, and the unpaired transverse arytenoid muscle.

The Muscles that tense the vocal cords include the paired cricothyroid muscle, as well as the vocalis muscle.

Laryngeal cavity. The cavity of the larynx is divided into three regions: the vestibule, the middle (interventricular) compartment, and the infraglottic cavity (Fig. 79).

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Fig. 79. Cavity of the larynx (coronal section):

1 — epiglottis; 2 — epiglottic tubercle; 3 — laryngeal vestibule; 4 — vestibular fold; 5 — laryngeal ventricle; 6 — vocal fold; 7 — thyroid cartilage; 8 — rima glottidis; 9 — infraglottic cavity; 10 — tracheal cavity; 11 — cricoid cartilage; 12 — lateral cricoarytenoid muscle; 13 — vocalis muscle; 14 — thyroarytenoid muscle; 15 — rima vestibuli

The Vestibule of the larynx extends from the laryngeal inlet to the vestibular folds. The vestibular folds are formed by the laryngeal mucosa, which contains mucous glands and thickened elastic fibers. The rima vestibuli is located between these folds.

The middle compartment—the interventricular space—is the narrowest. It extends from the vestibular folds above to the vocal folds below. On the left and right sides of the larynx, the laryngeal ventricles are located between the vestibular folds (false vocal cords) and the vocal folds. The right and left vocal folds bound the rima glottidis, which is the narrowest part of the laryngeal cavity. The rima glottidis is divided into the intermembranous and intercartilaginous parts. The length of the rima glottidis is 20–24 mm in men and 16–19 mm in women; its width is 5 mm during quiet breathing and up to 15 mm during phonation.

The inferior region of the laryngeal cavity, which transitions into the trachea, is called the infraglottic cavity.

The larynx has three layers: the mucosa, the fibrocartilaginous layer, and the adventitia (connective tissue layer). The mucosa is lined with pseudostratified ciliated columnar epithelium, except over the vocal cords. The fibrocartilaginous layer consists of hyaline and elastic cartilages. These, in turn, are surrounded by dense Fibrous connective tissue and serve as the structural framework of the larynx.

During phonation, the rima glottidis is closed and opens only when air pressure in the infraglottic cavity increases during exhalation. The air passing from the Lungs into the larynx causes the vocal cords to vibrate. This produces sounds of varying pitch and intensity. The laryngeal muscles, which constrict and dilate the rima glottidis, participate in sound formation. In addition, phonation depends on the state of the resonators (Nasal cavity, Paranasal Sinuses, Pharynx), age, sex, and the function of the vocal apparatus. The Central Nervous system also plays a role in phonation, controlling the vocal cords and laryngeal muscles. In children, the larynx is smaller than in adults, the vocal cords are shorter, and the pitch of the voice is higher. The dimensions of the larynx can change during Puberty, which leads to voice mutation.