Innovation of the Intrinsic Muscles of the Larynx

Relevant Anatomy

• Hyoid Bone: Located at the top, colored gold.
• Thyroid Cartilage: Colored blue.
• Cricoid Cartilage: Present below the thyroid cartilage.
• Trachea: Located below the cricoid cartilage.
• Thyrohyoid Membrane: Stretches between the hyoid bone and the thyroid cartilage.

Vocal Cords

• Situated inside the larynx, involved in phonation.

Innervation Overview

• All innervation to the vocal cords is by the Vagus Nerve.
• The Vagus Nerve has different branches involved in this innervation:
  • Recurrent Laryngeal Nerves
  • Superior Laryngeal Nerves

Vagus Nerve

• Located on both left and right sides of the neck.
• Fibers originate from the Inferior Vagal Ganglia high in the neck.
• Descends medial to the internal carotid artery, dividing into branches.

Recurrent Laryngeal Nerves

• Branches of the Vagus Nerve.
• Different courses:
  • Left Side: Dips lower around the arch of the aorta.
  • Right Side: Courses around the subclavian artery.
• Function: Supplies all intrinsic laryngeal muscles except the cricothyroid.
• Sensory Role: Sensory below the vocal folds.

Superior Laryngeal Nerve

• Divides into two branches:
  • Internal Branch:
    • Mainly sensory.
    • Supplies sensory innervation above the vocal folds.
  • External Branch:
    • Motor to the cricothyroid muscle only.

Functionality of Innervation

• External Branch of Superior Laryngeal Nerve:
  • Motor supply to cricothyroid muscle.
• Internal Branch of Superior Laryngeal Nerve:
  • Sensory above vocal folds.
• Recurrent Laryngeal Nerve:
  • Motor supply to all intrinsic muscles of larynx except cricothyroid.
  • Sensory below vocal folds.

Conclusion

• Two main nerves innervate the intrinsic muscles of the larynx:
  • Recurrent laryngeal nerves
  • Superior laryngeal nerve (with internal and external branches)

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