Larynx

1. Overview

The larynx, commonly referred to as the “voice box,” is a hollow muscular and cartilaginous structure located in the upper airway. It plays essential roles in phonation (voice production), airway protection, respiration, and cough reflex regulation. The larynx houses the vocal folds, which vibrate to produce sound, and functions as a protective valve to prevent aspiration of food into the lower respiratory tract.

2. Location

The larynx is located in the anterior neck, spanning from the level of C3 to C6 vertebrae in adults. Anatomical boundaries include:

• Superiorly: Continuous with the laryngopharynx at the level of the epiglottis

• Inferiorly: Transitions into the trachea at the level of the cricoid cartilage

• Anteriorly: Lies behind the infrahyoid muscles and is palpable beneath the skin

• Posteriorly: In contact with the esophagus

3. Structure

The larynx is composed of cartilages, muscles, ligaments, and mucosa arranged to form a specialized structure for breathing, speaking, and swallowing.

Cartilages

The laryngeal framework consists of nine cartilages:

• Unpaired: Thyroid, cricoid, and epiglottis

• Paired: Arytenoid, corniculate, and cuneiform (x2 each)

Muscles

• Intrinsic muscles: Control vocal fold movement (e.g., cricothyroid, posterior cricoarytenoid, thyroarytenoid)

• Extrinsic muscles: Move the larynx as a whole (e.g., sternothyroid, thyrohyoid)

Vocal Folds and Glottis

• True vocal cords (vocal folds): Vibrate to produce sound

• False vocal cords (vestibular folds): Assist in closure during swallowing

• Rima glottidis: Opening between vocal folds, changes size during respiration and phonation

Cavity

The laryngeal cavity is divided into three regions:

• Supraglottic: Above the vocal folds (includes epiglottis and vestibule)

• Glottic: Level of the vocal folds

• Subglottic: Below the vocal folds to the cricoid cartilage

Innervation

• Vagus nerve (CN X): Via its branches:

• Superior laryngeal nerve: External branch to cricothyroid; internal branch provides sensation above the vocal cords

• Recurrent laryngeal nerve: Motor to intrinsic muscles (except cricothyroid) and sensory below the vocal cords

4. Function

The larynx performs several vital functions:

• Voice production: Vibrating vocal folds create sound when air is expelled from the lungs

• Airway protection: Closes during swallowing to prevent aspiration into the lungs

• Respiratory control: Regulates airflow resistance during breathing

• Cough reflex: Acts as a reflex gate to expel irritants or foreign material

5. Physiological Role(s)

The larynx integrates into respiratory physiology in several ways:

• Breathing: Opens during inhalation and exhalation; posterior cricoarytenoid muscles abduct the vocal cords to widen the airway

• Swallowing: Larynx elevates and glottis closes to direct food toward the esophagus

• Speech and phonation: Modulates pitch and volume through tension adjustments of the vocal folds (via cricothyroid and thyroarytenoid muscles)

• Valsalva maneuver: Forceful closure increases intrathoracic pressure for coughing, defecation, and childbirth

6. Clinical Significance

Laryngitis

Inflammation of the vocal cords due to infection, overuse, or irritants. Symptoms include hoarseness, sore throat, and voice loss. Usually self-limited but may become chronic in professionals or smokers.

Laryngeal Cancer

Commonly involves the glottis or supraglottic region. Risk factors include smoking, alcohol, and HPV. Symptoms include:

• Persistent hoarseness

• Dysphagia

• Referred otalgia (ear pain)

Diagnosed by laryngoscopy and biopsy. Treated with surgery, radiation, or chemotherapy depending on stage.

Vocal Cord Paralysis

Caused by damage to the recurrent laryngeal nerve (e.g., during thyroidectomy, tumor compression). Results in:

• Breathiness of voice

• Aspiration risk

• Stridor (if bilateral)

Treated with voice therapy or surgical medialization procedures.

Laryngospasm

Sudden involuntary closure of the vocal cords, often triggered by irritants, GERD, or anesthesia. May cause temporary inability to breathe or speak. Managed with reassurance and airway support if severe.

Laryngeal Obstruction

Can occur due to edema (e.g., anaphylaxis), trauma, or foreign body. Rapid airway compromise necessitates emergency management such as cricothyrotomy or tracheostomy.

Intubation and Airway Management

The larynx is the key structure visualized during endotracheal intubation. Landmarks such as the epiglottis, vocal cords, and glottic opening are critical for safe airway access.