M01.04.006 Larynx

The larynx, or voice box, is a cartilaginous organ located in the anterior neck. It serves as a component of the respiratory tract and is vital for phonation, the cough reflex, and protection of the lower respiratory tract. This guide explores its anatomy, including its position, structure, vasculature, innervation, and clinical relevance.

Anatomical Position and Relations

Position

• Located in the anterior compartment of the neck.
• Suspended from the hyoid bone, extending between C3 and C6 vertebrae.
• Superiorly opens into the laryngeal part of the pharynx.
• Inferiorly continuous with the trachea.

Surrounding Structures

• Anteriorly: Covered by the infrahyoid muscles.
• Laterally: Adjacent to the thyroid gland lobes and major blood vessels of the neck.
• Posteriorly: Lies against the esophagus, significant during procedures like cricoid pressure (Sellick’s maneuver) to prevent regurgitation during intubation.

Anatomical Structure

Cartilaginous Framework

• Held together by ligaments and membranes.
• Moved by laryngeal muscles for phonation and respiration.

Internal Cavity Sections

1. Supraglottis: Extends from the inferior epiglottis to vestibular folds (false vocal cords).
2. Glottis: Houses vocal cords and includes the rima glottidis, an opening between the cords that adjusts via phonation muscles.
3. Subglottis: Spans from the glottis’s inferior border to the cricoid cartilage’s lower edge.

Epithelium

• Lined by pseudostratified Ciliated columnar epithelium, except for the true vocal cords, which are covered by stratified squamous epithelium.

Vasculature

Arterial Supply

• Superior laryngeal artery: Branch of the superior thyroid artery (from external carotid artery).
• Inferior laryngeal artery: Branch of the inferior thyroid artery (from thyrocervical trunk).

Venous Drainage

• Superior laryngeal vein: Drains into the internal jugular vein.
• Inferior laryngeal vein: Drains into the left brachiocephalic vein.

Innervation

Motor and Sensory Nerves

• Recurrent laryngeal nerve (branch of vagus):
  • Motor: All intrinsic muscles except cricothyroid.
  • Sensory: Infraglottis.
• Superior laryngeal nerve (branch of vagus):
  • Internal branch: Sensory to Supraglottis.
  • External branch: Motor to the cricothyroid muscle.

Clinical Relevance

Vocal Cord Paralysis

• Controlled by intrinsic laryngeal muscles, primarily innervated by the recurrent laryngeal nerve.

Causes of Recurrent Laryngeal Nerve (RLN) Palsy:

1. Apical lung tumors.
2. Thyroid cancer.
3. Aortic aneurysm.
4. Cervical lymphadenopathy.
5. Iatrogenic injury during thyroid surgery.

Manifestations:

• Unilateral RLN palsy:
  • One cord was paralyzed.
  • Hoarseness of voice; speech usually compensated.
• Bilateral RLN palsy:
  • Both cords are paralyzed, impairing breathing and phonation.
  • If cords are fully adducted, emergency surgical intervention is required.

Points to Remember

1. The larynx is crucial for voice production and airway protection.
2. Its cartilaginous structure is held together by ligaments, with specialized muscles for phonation and respiration.
3. The recurrent laryngeal nerve is highly susceptible to damage during surgical procedures.
4. Cricoid pressure is a clinical maneuver used to prevent gastric regurgitation during intubation.
5. Damage to laryngeal nerves can lead to vocal cord paralysis, affecting speech and breathing.

Summary Table: Larynx Anatomy

Bibliography

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy.
• Netter, F. H. (2019). Atlas of Human Anatomy.
• Tortora, G. J., & Derrickson, B. (2017). Principles of Anatomy and Physiology.