Laryngeal Structures

The larynx, commonly known as the voice box, is composed of a complex arrangement of cartilages, muscles, ligaments, and membranes. Collectively, these components are referred to as the laryngeal structures. These elements work together to perform vital functions, including phonation, respiration, and protection of the lower respiratory tract during swallowing.

Location

The laryngeal structures are located in the anterior region of the neck, extending from the level of the third to sixth cervical vertebrae in adults. They sit between the pharynx (above) and the trachea (below), just inferior to the hyoid bone and anterior to the esophagus.

Cartilaginous Framework

The larynx is built around a framework of cartilages that provide structural support and maintain an open airway. These cartilages are divided into paired and unpaired types:

Unpaired Cartilages

• Thyroid cartilage: The largest laryngeal cartilage, forming the laryngeal prominence or "Adam's apple".
• Cricoid cartilage: A complete ring of cartilage located inferior to the thyroid cartilage; it marks the transition from the larynx to the trachea.
• Epiglottis: A leaf-shaped elastic cartilage that acts as a lid over the glottis during swallowing, preventing food from entering the airway.

Paired Cartilages

• Arytenoid cartilages: Pyramid-shaped structures that sit atop the cricoid cartilage posteriorly and anchor the vocal folds.
• Corniculate cartilages: Small, horn-like cartilages that sit on the apices of the arytenoids, helping to support the posterior part of the vocal folds.
• Cuneiform cartilages: Small rod-like cartilages located in the aryepiglottic folds, providing structural support to soft tissues.

Laryngeal Muscles

The muscles of the larynx are categorized as intrinsic and extrinsic. Intrinsic muscles control the tension and position of the vocal folds, while extrinsic muscles move the entire larynx during swallowing or speech.

Intrinsic Muscles

• Cricothyroid: Stretches and tenses the vocal folds, increasing pitch.
• Thyroarytenoid: Relaxes the vocal folds by shortening them.
• Posterior cricoarytenoid: The only muscle that abducts (opens) the vocal folds.
• Lateral cricoarytenoid: Adducts (closes) the vocal folds.
• Transverse and oblique arytenoids: Draw the arytenoid cartilages together, assisting in vocal fold adduction.
• Vocalis: Fine-tunes tension in specific parts of the vocal folds.

Extrinsic Muscles

• Suprahyoid group (e.g., mylohyoid, digastric, geniohyoid): Elevate the larynx during swallowing.
• Infrahyoid group (e.g., sternothyroid, thyrohyoid): Depress the larynx after elevation.

Ligaments and Membranes

Several connective tissue structures help hold the laryngeal cartilages in position and facilitate movement:

• Thyrohyoid membrane: Connects the thyroid cartilage to the hyoid bone.
• Cricothyroid ligament: Connects the cricoid and thyroid cartilages; important in emergency airway access (cricothyrotomy).
• Quadrangular membrane: Forms the vestibular (false vocal) folds.
• Conus elasticus: Forms the vocal (true vocal) ligaments.

Glottic Structures

The glottis is the central component of the larynx involved in sound production.

• Vocal folds (true vocal cords): Consist of the vocal ligament and vocalis muscle; they vibrate to produce sound.
• Vestibular folds (false vocal cords): Located above the true vocal cords, play a role in airway protection.
• Rima glottidis: The opening between the true vocal folds; changes in shape and size during respiration and phonation.

Vascular Supply

The laryngeal structures receive blood supply from:

• Superior laryngeal artery (branch of the superior thyroid artery)
• Inferior laryngeal artery (branch of the inferior thyroid artery)

Innervation

Laryngeal function is controlled by branches of the vagus nerve (cranial nerve X):

• Superior laryngeal nerve:
  • External branch: Supplies cricothyroid muscle.
  • Internal branch: Provides sensory innervation above the vocal folds.
• Recurrent laryngeal nerve: Innervates all intrinsic muscles (except cricothyroid) and provides sensory input below the vocal folds.

Clinical Relevance

• Laryngitis: Inflammation of the vocal cords, leading to hoarseness or loss of voice.
• Vocal cord paralysis: May result from injury to the recurrent laryngeal nerve, affecting phonation and breathing.
• Cricoid pressure (Sellick maneuver): Used during intubation to occlude the esophagus and reduce aspiration risk.
• Cricothyrotomy: Emergency airway procedure accessing the airway via the cricothyroid membrane.