Larynx

Larynx

I. Introduction

• Is the organ of voice production and the part of the respiratory tract between the lower part of the pharynx and the trachea.
• Acts as a compound sphincter to prevent the passage of food or drink into the airway in swallowing and to close the rima glottidis during the Valsalva maneuver (buildup of air pressure
• during coughing, sneezing, micturition, defecation, or parturition).
• Regulates the flow of air to and from the lungs for vocalization (phonation).
• Forms a framework of cartilage for the attachment of ligaments and muscles.

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II. Cartilages

A. Thyroid cartilage

• Is a single hyaline cartilage that forms a median elevation called the laryngeal prominence (Adam's apple) , which is particularly apparent in males.
• Has an oblique line on the lateral surface of its lamina that gives attachment for the inferior pharyngeal constrictor, sternothyroid, and thyrohyoid muscles.

B. Cricoid cartilage

• Is a single hyaline cartilage that is shaped like a signet ring.
• Is at the level of CV6 and articulates with the thyroid cartilage. Its lower border marks the end of the pharynx and larynx.

C. Epiglottis

• Is a single elastic cartilage.
• Is a spoon-shaped plate that lies behind the root of the tongue and forms the superior part of the anterior wall of the larynx.
• Its lower end is attached to the back of the thyroid cartilage.

D. Arytenoid cartilages

• Are paired elastic and hyaline cartilages.
• Are shaped liked pyramids, with bases that articulate with and rotate on the cricoid cartilage.
• Have vocal processes , which give attachment to the vocal ligament and vocalis muscle, and muscular processes , which give attachment to the thyroarytenoid muscle and the lateral and posterior cricoarytenoid muscles.
• Sits on the top of the cricoid cartilage and rotates to change the opening of the vocal folds (the rima glottidis).

E. Corniculate cartilages

• Are paired elastic cartilages that lie on the apices of the arytenoid cartilages.
• Are enclosed within the aryepiglottic folds of mucous membrane.

F. Cuneiform cartilages

• Are paired elastic cartilages that lie in the aryepiglottic folds anterior to the corniculate cartilages.

III. Ligaments of the Larynx

A. Thyrohyoid membrane

• Extends from the thyroid cartilage to the medial surface of the hyoid bone.
• Its middle (thicker) part is called the middle thyrohyoid ligament , and its lateral portion is pierced by the internal laryngeal nerve and the superior laryngeal vessels.

B. Cricothyroid ligament

• Extends from the arch of the cricoid cartilage to the thyroid cartilage and the vocal processes of the arytenoid cartilages.

C. Vocal ligament

• Extends from the posterior surface of the thyroid cartilage to the vocal process of the arytenoid cartilage.
• Is considered the upper border of the conus elasticus.

D. Vestibular (ventricular) ligament

• Extends from the thyroid cartilage to the anterior lateral surface of the arytenoid cartilage.

E. Conus elasticus (cricovocal ligament)

• Is the paired lateral portion of the fibroelastic membrane that extends between the superior border of the entire arch of the cricoid cartilage and the vocal ligaments.
• Is formed by the cricothyroid, median cricothyroid, and vocal ligaments.

IV. Cavities and Folds

• The laryngeal cavity is divided into three portions by the vestibular and vocal folds: the vestibule, ventricle, and infraglottic cavity.

A. Vestibule

• Extends from the laryngeal inlet to the vestibular (ventricular) folds.

B. Ventricles

• Extend between the vestibular fold and the vocal fold.

C. Infraglottic cavity

• Extends from the rima glottidis to the lower border of the cricoid cartilage.

D. Rima glottidis

• Is the space between the vocal folds and arytenoid cartilages.
• Is the narrowest part of the laryngeal cavity

E. Vestibular folds (false vocal cords)

• Extend from the thyroid cartilage above the vocal ligament to the arytenoid cartilage.

F. Vocal folds (true vocal cords)

• Extend from the angle of the thyroid cartilage to the vocal processes of the arytenoid cartilages.
• Contain the vocal ligament near their free margin and the vocalis muscle , which forms the bulk of the vocal fold.
• Are important in voice production because they control the stream of air passing through the rima glottidis.
• Alter the shape and size of the rima glottides by movement of the arytenoids to facilitate respiration and phonation. (The rima glottidis is wide during inspiration and narrow and wedge-shaped during expiration and sound production.)

V. Muscles

Muscles of the larynx.

Muscle Cricothyroid
Origin Arch of cricoid cartilage
Insertion Inferior horn and lower lamina of thyroid cartilage
Nerve External laryngeal
Action on Vocal Cords Tenses; adducts; elongates

Muscle Posterior cricoarytenoid*
Origin Posterior surface of lamina of cricoid cartilage
Insertion Muscular process of arytenoid cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Abducts; opens rima glottidis by rotating arytenoid cartilage laterally

Muscle Lateral cricoarytenoid
Origin Arch of cricoid cartilage
Insertion Muscular process of arytenoid cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts; closes rima glottidis by rotating arytenoid cartilage medially

Muscle Transverse arytenoid
Origin Posterior surface of arytenoid cartilage
Insertion Opposite arytenoid cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts; closes rima glottidis

Muscle Oblique arytenoid
Origin Muscular process of arytenoid cartilage
Insertion Apex of opposite arytenoid
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts; closes rima glottidis

Muscle Aryepiglottic
Origin Apex of arytenoid cartilage
Insertion Side of epiglottic cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts

Muscle Thyroarytenoid
Origin Inner surface of thyroid lamina
Insertion Anterolateral surface of arytenoid cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts; relaxes

Muscle Thyroepiglottic
Origin Anteromedial surface of lamina of thyroid cartilage
Insertion Lateral margin of epiglottic cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts

Muscle Vocalis
Origin Angle between two laminae of thyroid cartilage
Insertion Vocal process of arytenoid cartilage
Nerve Recurrent laryngeal
Action on Vocal Cords Adducts; tenses (anterior part); relaxes (posterior part); controls pitch

*The posterior cricoarytenoid muscle draws the muscular process of the arytenoid cartilage posteriorly and thereby rotates the vocal process laterally, resulting in opening of the rima glottidis, whereas the lateral cricoarytenoid muscle draws the muscular process anteriorly and thereby rotates the vocal process medially.

VI. Innervation

A. Recurrent laryngeal nerve

• Innervates all of the intrinsic muscles of the larynx except the cricothyroid, which is innervated by the external laryngeal branch of the superior laryngeal branch of the vagus nerve.
• Supplies sensory innervation below the vocal cord.
• Has a terminal portion above the lower border of the cricoid cartilage called the inferior laryngeal nerve.

B. Superior laryngeal nerve

• Is a branch of the vagus nerve and divides into the internal and external laryngeal branches.

C. Internal laryngeal nerve

• Innervates the mucous membrane above the vocal cord and taste buds on the epiglottis.
• Is accompanied by the superior laryngeal artery and pierces the thyrohyoid membrane.

D. External laryngeal nerve

• Innervates the cricothyroid and inferior pharyngeal constrictor (cricopharyngeus part) muscles.
• Is accompanied by the superior thyroid artery.

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