Larynx

Introduction:

• Organ of voice production and a portion of the respiratory tract between the lower throat and the trachea
• Acts as a complex sphincter to prevent food or water from entering the airway during swallowing and to shut the rima glottidis during the Valsalva maneuver (buildup of air pressure during coughing, sneezing, micturition, defecation, or parturition).
• Controls the movement of air to and from the lungs in preparation for vocalization (phonation).
• Forms a cartilage scaffolding for the attachment of ligaments and muscles
  
• Laryngitis is an inflammation of the mucous membrane of the larynx that causes throat dryness and pain, hoarseness, coughing, and dysphagia.

Cartilage:

• The thyroid cartilage is a single hyaline cartilage that forms a median elevation: Laryngeal prominence (Adam's apple), which is more visible in males. It has an oblique line on the lateral surface of its lamina that provides attachment for the inferior pharyngeal constrictor, sternothyroid, and thyrohyoid muscles.
• Cricoid Cartilage is a single hyaline cartilage that is fashioned like a signet ring and articulates with the thyroid cartilage at the level of Cervical Vertebrae 6. Its bottom border delineates the pharynx and larynx.
• The epiglottis is a single piece of elastic cartilage having a spoon-shaped plate that constitutes the superior section of the front wall of the larynx and lies behind the root of the tongue. It is linked to the rear of the thyroid cartilage at its lower end. Epiglottitis is an inflammation or acute mucosal swelling of the epiglottis that causes a potentially fatal airway blockage, particularly in youngsters.
• Arytenoid Cartilages are elastic and hyaline cartilages that are paired pyramid-shaped, with bases that articulate and spin on the cricoid cartilage, the vocal processes that attach to the vocal ligament and vocalis muscle, as well as muscular processes that attach to the thyroarytenoid muscle and the lateral and posterior cricoarytenoid muscles. Rotates to adjust the openness of the vocal folds while sitting on top of the cricoid cartilage (rima glottidis).
• Corniculate cartilages are paired elastic cartilages found on the apices of arytenoid cartilages and contained inside the mucosal membrane's aryepiglottic folds.
• Cuneiform Cartilages are paired elastic cartilages that are anterior to the corniculate cartilages in the aryepiglottic folds.

Ligaments

Thyrohyoid Membrane: 

• The Thyrohyoid Membrane Reaches the medial surface of the hyoid bone from the thyroid cartilage. The middle thyrohyoid ligament, which is its center and thicker portion, and the lateral both the superior laryngeal arteries and the internal laryngeal nerve were punctured. A laryngotomy is an operation that involves making an opening into the larynx through the cricothyroid membrane, the thyroid cartilage, or the thyrohyoid membrane (superior laryngotomy). It is carried out when a foreign body or acute edema calls for an immediate airway into the larynx and trachea.

Cricothyroid Ligament:

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

Vocal Ligament:

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

Vestibular (Ventricular) Ligament:

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

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.

CAVITIES AND FOLDS

The laryngeal cavity is divided into 3 portions by vestibular & vocal folds: Vestibule, Ventricle & Infraglottic cavity

• Vestibule: Extends from the laryngeal inlet to the vestibular (ventricular) folds.
• Ventricles: Extend between the vestibular fold and the vocal fold.
• Infraglottic Cavity: Extends from the rima glottidis to the lower border of the cricoid cartilage.
• Rima Glottidis: is the space between the vocal folds and arytenoid cartilages & narrowest part of the laryngeal cavity.
• Vestibular Folds (False Vocal Cords): Extend from the thyroid cartilage above the vocal ligament to the arytenoid cartilage.
• Vocal Folds (True Vocal Cords): Extend from the angle of the thyroid cartilage to the vocal processes of the arytenoid cartilages that Contain the vocal ligament near their free margin and vocalis muscle, which forms the bulk of the vocal fold. 
• Are important in voice production because they control the stream of air passing through rima glottidis.Alter the shape and size of the rima glottidis by the 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.)

INNERVATION

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.
• Lesion of the recurrent laryngeal nerve could be produced during thyroidectomy or cricothyrotomy or by aortic aneurysm and may cause respiratory obstruction, hoarseness, inability to speak, and loss of sensation below the vocal cord.

Superior Laryngeal Nerve

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

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.
• Lesion of the internal laryngeal nerve results in loss of sensation above the vocal cord and loss of taste in the epiglottis.

External Laryngeal Nerve

• Innervates the cricothyroid and inferior pharyngeal constrictor (cricopharyngeus part) muscles.
• Is accompanied by the superior thyroid artery
• Lesion of the external laryngeal nerve may occur during thyroidectomy because the nerve accompanies the superior thyroid artery. It causes paralysis of the cricothyroid muscle, resulting in paralysis of the laryngeal muscles and thus the inability to lengthen the vocal cord and loss of the tension of the vocal cord. Such stresses to the vocal cord cause a fatigued voice and a weak hoarseness

References:

Halliday NL, Chung HM. BRS Gross anatomy. 9th ed. Philadelphia: Wolters Kluwer Health; 2020.