Nerve Supply of Larynx - Recurrent Laryngeal Nerve and Superior Laryngeal Nerve
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🔌 Nerve Supply of Larynx – Recurrent Laryngeal Nerve and Superior Laryngeal Nerve
🧠 Overview of Laryngeal Innervation
The vagus nerve (cranial nerve X) gives rise to both the recurrent laryngeal nerve and the superior laryngeal nerve, which together supply the larynx.
⚙️ Motor Supply of Larynx
All intrinsic muscles of the larynx are supplied by the recurrent laryngeal nerve, except Cricothyroid, which is supplied by the External branch of the Superior laryngeal nerve.
👂 Sensory Supply of Larynx
- Above the vocal cords: Supplied by the Internal branch of the Superior laryngeal nerve.
- Below the vocal cords: Supplied by the Recurrent laryngeal nerve.
🔄 Recurrent Laryngeal Nerve (RLN)
🧬 Origin
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Right RLN:
- Arises at the root of the neck from the right vagus nerve (level of T1).
- Loops around the first part of the right subclavian artery.
-
Left RLN:
- Arises in the thorax as the left vagus crosses the aortic arch (level of T3).
- Loops around the arch of the aorta, posterior to ligamentum arteriosum.
🛣️ Course
- Ascends in the tracheoesophageal groove.
- Passes deep to the lower border of the inferior constrictor.
- Enters the larynx behind the cricothyroid joint.
🧪 Nerve Supply
-
Motor: All intrinsic laryngeal muscles except cricothyroid.
-
Sensory: Mucosa below the vocal cords.
🧫 Developmental Basis
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Left RLN hooks under the arch of aorta due to persistence of the dorsal part of the 6th aortic arch (ligamentum arteriosum).
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Right RLN hooks under the 4th aortic arch (right subclavian artery), as the 5th and 6th arches regress.
Why is Recurrent Laryngeal Nerve longer in the left side than the right side?
What is Non-Recurrent Laryngeal Nerve?
📡 Superior Laryngeal Nerve (SLN)
🧬 Origin
-
Arises from the inferior ganglion of vagus in the neck.
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Receives a twig from the superior cervical sympathetic ganglion.
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Divides into:
- External branch (Motor)
- Internal branch (Sensory)
🌿 Branches and Course
🔧 External Branch
- Supplies: Cricothyroid muscle
- Travels with: Superior thyroid artery
- Passes deep to: Upper thyroid pole
🌬️ Internal Branch
- Pierces: Thyrohyoid membrane
- Supplies:
- Mucosa above the vocal cords
- Glands via parasympathetic secretomotor fibers
🧵 Terminal Branches of Internal SLN:
- Superior branch → Lingual surface of epiglottis
- Middle branch → Aryepiglottic fold and vestibular folds
- Inferior branch → Pyriform sinus and postcricoid region
- Forms anastomosis with recurrent laryngeal nerve → Galen's Anastomosis (purely sensory)
What is Human communicating nerve?
📋 Summary Table
| Nerve | Branch | Motor Supply | Sensory Supply |
|---|---|---|---|
| Recurrent Laryngeal Nerve | From Vagus (X) | All intrinsic muscles except cricothyroid | Below vocal cords |
| Superior Laryngeal Nerve – External | From Vagus (X) | Cricothyroid | — |
| Superior Laryngeal Nerve – Internal | From Vagus (X) | — | Above vocal cords, supraglottic larynx |
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