Larynx

The larynx, commonly known as the voice box, is a hollow, tubular structure in the respiratory system. It is composed of cartilage, muscles, and ligaments, forming a framework that houses the vocal cords. The larynx plays a vital role in producing sound, facilitating breathing, and protecting the airway during swallowing. It is lined with mucous membranes and supported by a complex arrangement of cartilage, including the thyroid cartilage, which forms the Adam’s apple.

Location

The larynx is located in the neck, positioned between the pharynx (throat) and the trachea (windpipe). It lies approximately at the level of the C3 to C6 vertebrae in the cervical spine.

Anatomy

1. Cartilaginous Framework

The larynx is primarily composed of nine cartilages, which are classified into three unpaired and three paired structures:

Unpaired Cartilages

1. Thyroid Cartilage
   • The largest cartilage in the larynx.
   • Forms the anterior and lateral walls.
   • Features the laryngeal prominence (Adam’s apple).
   • Superiorly connected to the hyoid bone via the thyrohyoid membrane and inferiorly to the cricoid cartilage via the cricothyroid ligament.
2. Cricoid Cartilage
   • Ring-shaped and located below the thyroid cartilage.
   • Forms a complete circle, with a narrow anterior arch and a broad posterior lamina.
   • Connects to the trachea via the cricotracheal ligament.
3. Epiglottis
   • Leaf-shaped, elastic cartilage situated posterior to the tongue.
   • Attached to the thyroid cartilage by the thyroepiglottic ligament.
   • Its free upper end projects upwards, forming part of the laryngeal inlet.

Paired Cartilages

1. Arytenoid Cartilages
   • Pyramid-shaped structures sitting atop the cricoid cartilage.
   • Serve as attachment points for the vocal cords and muscles.
   • Contain processes:
     • Vocal process (attachment for vocal ligaments).
     • Muscular process (attachment for intrinsic muscles).
2. Corniculate Cartilages
   • Small, horn-shaped cartilages located at the apex of the arytenoids.
   • Provide structural support to the aryepiglottic folds.
3. Cuneiform Cartilages
   • Small, rod-shaped cartilages embedded within the aryepiglottic folds.
   • Reinforce the folds and maintain the laryngeal opening.

2. Ligaments and Membranes

The cartilages of the larynx are connected by ligaments and membranes that provide structural support and flexibility.

Extrinsic Ligaments and Membranes

• Thyrohyoid Membrane – Connects the thyroid cartilage to the hyoid bone.
• Cricotracheal Ligament – Joins the cricoid cartilage with the first tracheal ring.
• Hyoepiglottic Ligament – Attaches the epiglottis to the hyoid bone.

Intrinsic Ligaments and Membranes

• Quadrangular Membrane – Extends from the epiglottis to the arytenoids, forming the vestibular folds (false vocal cords).
• Conus Elasticus – Extends from the cricoid cartilage upward to form the vocal ligaments within the true vocal cords.

3. Cavities and Compartments

The larynx is divided into three main compartments:

• Vestibule: The uppermost part, located between the laryngeal inlet and the vestibular folds (false vocal cords).
• Ventricle: A lateral recess between the vestibular folds (above) and vocal folds (below).
• Infraglottic Cavity: Extends from the vocal folds to the lower border of the cricoid cartilage, continuing into the trachea.

4. Vocal Folds (Cords)

The vocal cords are two pairs of folds:

• False Vocal Cords (Vestibular Folds)
  • Upper pair composed of mucosa and fibrous tissue.
  • Do not contribute to phonation.
• True Vocal Cords
  • Lower pair containing vocal ligaments and vocalis muscles.
  • Responsible for sound production.

5. Musculature

The muscles of the larynx are classified into extrinsic and intrinsic groups:

Extrinsic Muscles

• Attach the larynx to surrounding structures (e.g., hyoid bone) and move it as a whole.
• Include suprahyoid and infrahyoid muscles.

Intrinsic Muscles

• Control the position and tension of the vocal cords.
• Key muscles include:
  • Cricothyroid – Tenses the vocal cords.
  • Thyroarytenoid – Relaxes the vocal cords.
  • Posterior Cricoarytenoid – Abducts (opens) the vocal cords.
  • Lateral Cricoarytenoid – Adducts (closes) the vocal cords.
  • Transverse and Oblique Arytenoids – Bring the arytenoids together for closure.

6. Blood Supply

• Arteries
  • Superior laryngeal artery (branch of the superior thyroid artery).
  • Inferior laryngeal artery (branch of the inferior thyroid artery).
• Veins
  • Drainage occurs through superior and inferior laryngeal veins into the internal jugular vein.

7. Nerve Supply

Innervation is provided by branches of the vagus nerve (CN X):

• Superior Laryngeal Nerve
  • External Branch – Motor supply to the cricothyroid muscle.
  • Internal Branch – Sensory innervation to the mucosa above the vocal cords.
• Recurrent Laryngeal Nerve
  • Provides motor innervation to all intrinsic muscles (except cricothyroid) and sensory innervation below the vocal cords.

8. Lymphatic Drainage

• Above Vocal Cords – Drains into the deep cervical lymph nodes.
• Below Vocal Cords – Drains into the pretracheal and paratracheal lymph nodes.

Function

1. Airway Protection

The larynx acts as a guardian of the airway, preventing food, liquids, and foreign particles from entering the trachea and lungs.

Mechanisms of Protection:

• Epiglottis Closure: The epiglottis folds backward to cover the laryngeal inlet during swallowing, blocking the entry of food and liquids into the airway.
• False Vocal Cords (Vestibular Folds): These folds act as an additional barrier, providing a secondary layer of protection.
• Cough Reflex: The laryngeal mucosa is highly sensitive and triggers a cough reflex when irritants are detected, forcibly expelling them from the airway.
• Laryngeal Elevation: During swallowing, the larynx elevates, facilitating epiglottis closure and directing food into the esophagus instead of the trachea.

2. Phonation (Sound Production)

The larynx is the primary organ for voice production due to the vocal cords (true vocal folds).

Mechanisms of Sound Generation:

• Vibration of Vocal Cords:
  • Air from the lungs passes through the glottis, causing the vocal cords to vibrate and produce sound waves.
• Tension and Length Control:
  • Intrinsic muscles adjust the tension, length, and thickness of the vocal cords, modulating pitch and tone.
  • Cricothyroid muscle tightens the cords, producing higher-pitched sounds, while thyroarytenoid muscles relax them for lower-pitched sounds.
• Resonance and Articulation:
  • Sound produced by the larynx is shaped into speech by the pharynx, oral cavity, tongue, teeth, and lips.

3. Respiration (Air Passage)

The larynx acts as a conduit for airflow between the pharynx and trachea during breathing.

Mechanisms of Air Passage Control:

• Glottis Regulation:
  • The size of the glottis (space between the vocal cords) can be adjusted by intrinsic muscles to regulate airflow.
  • Posterior cricoarytenoid muscles abduct (open) the vocal cords to maximize airflow during inspiration.
  • Lateral cricoarytenoid muscles adduct (close) the vocal cords partially to modulate airflow during activities like speech or whispering.
• Maintenance of Patency:
  • The rigid cartilage framework ensures that the airway remains open under normal conditions.

4. Intrathoracic Pressure Regulation (Valsalva Maneuver)

The larynx assists in generating intrathoracic pressure for actions requiring forceful exertion.

Mechanism

• The vocal cords are tightly adducted to seal the glottis, temporarily blocking airflow.
• This creates pressure in the thorax and abdomen, enabling activities like:
  • Coughing – Expels mucus and foreign particles.
  • Sneezing – Clears irritants from the nasal cavity.
  • Straining – Provides stability during activities like lifting heavy objects, childbirth, or defecation.

5. Swallowing (Deglutition)

The larynx facilitates safe swallowing by preventing food and liquids from entering the respiratory tract.

Mechanism During Swallowing:

• The larynx elevates and moves anteriorly, creating space for the epiglottis to fold down and seal the laryngeal inlet.
• The false vocal cords and true vocal cords close tightly, ensuring no particles pass into the trachea.
• Once swallowing is complete, the larynx returns to its resting position, reopening the airway for breathing.

6. Reflex Actions

The larynx plays a central role in mediating reflex actions that protect the respiratory system:

• Cough Reflex: Initiated by irritation of the laryngeal mucosa, forcing air out to expel foreign particles.
• Sneezing Reflex: Works in conjunction with the nasal cavity to clear irritants.
• Gag Reflex: Prevents choking by triggering muscle contractions in response to pharyngeal stimulation.

7. Emotional and Non-Verbal Communication

The larynx enables non-verbal vocalizations like laughing, crying, screaming, and groaning, which are important for expressing emotions and social interaction.

Mechanism

Changes in pitch, volume, and intonation are controlled by fine adjustments in the vocal cords and laryngeal muscles.

8. Phonation During Speech

The larynx is integral to spoken language, providing the raw sound that is shaped into speech by the articulatory organs.

• Vibratory Control: Vibration rate controls pitch. Faster vibrations yield higher tones, while slower vibrations produce lower tones.
• Volume Modulation: Adjustments in subglottic pressure (pressure below the vocal cords) regulate the loudness of sound.
• Articulation and Resonance: Sound waves resonate through the pharynx, oral cavity, and nasal cavity, shaping distinct sounds required for language.

9. Thermoregulation

Though not a primary function, the larynx plays a minor role in thermoregulation by assisting in heat exchange through airflow modulation during breathing, especially under conditions of exercise or stress.

Clinical Significance

The larynx is critically important in breathing, phonation, and airway protection, making it vulnerable to a range of diseases and disorders.

• Laryngeal Infections: Laryngitis (inflammation of the larynx) often results from viral infections, leading to hoarseness or loss of voice.
• Obstruction and Stridor: Airway obstruction caused by trauma, swelling, or foreign bodies can lead to stridor (high-pitched breathing sounds) and may require emergency airway management.
• Vocal Cord Paralysis: Damage to the recurrent laryngeal nerve can result in vocal cord paralysis, causing hoarseness, breathy voice, or even airway compromise in severe cases.
• Laryngeal Cancer: Squamous cell carcinoma of the larynx is common, especially in smokers and alcohol users, often presenting with persistent hoarseness or difficulty swallowing.
• Laryngospasm: Sudden involuntary closure of the vocal cords can cause difficulty breathing, often triggered by irritants, GERD, or anesthesia complications.
• Intubation and Surgery: The larynx is frequently involved in endotracheal intubation and tracheostomy procedures to maintain an open airway during emergencies or surgeries.
• Voice Disorders: Conditions like vocal cord nodules, polyps, or cysts affect voice quality and may require speech therapy or surgical intervention.
• Neurological Conditions: Disorders such as spasmodic dysphonia result from abnormal neural control, leading to involuntary vocal cord spasms and speech difficulties.