External Laryngeal Nerve

• The superior laryngeal nerve separates from the vagus nerve at the base of the skull and descends toward the superior pole of the thyroid along the internal carotid artery
• At the level of the hyoid cornu it divides into 2 branches
• The smaller external branch continues to travel along the lateral surface of the inferior pharyngeal constrictor muscle and usually descends anteriorly and medially along with the superior thyroid artery, to enter the cricothyroid muscle.
• Supplies cricothyroid which adducts the vocal cords
• Internal branch supplies mucosa above vocal cords
  • Internal Laryngeal Nerve
    • Pieces the Thyrohyoid Membrane to supply the mucosa in the Pharynx and Larynx above the vocal fold
  • External Laryngeal Nerve
    • Supplies the Cricothyroid muscles (only muscle in larynx not supplied by the Recurrent Laryngeal Nerve)

Anatomy

• Lies on Inferior Constrictor
• Close behind the Superior Thyroid Artery
• Runs down medial to the upper pole
• Supplies Cricothyroid
  • Cricothyroid tenses the vocal cords
  • Division of External Laryngeal Nerve results in flaccidity of the vocal fold

Cernea Classification

• Categorizes relationship between External Laryngeal Nerve and Superior Thyroid Artery
• Type 1:
  • Nerve crosses the Superior Thyroid Vessels > 1cm above the upper pole of
  • Thyroid
• Type 2a:
  • Crosses the Superior Thyroid vessels < 1cm above the upper pole of Thyroid
• Type 2b:
  • Crosses at or below level of upper pole of Thyroid