Superior laryngeal nerve !

The superior laryngeal nerve, a branch of the vagus, gives feeling inside the upper voice box and tightens the vocal cords for high notes.

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What it is

A vagus branch high in the neck with an internal and an external branch.

What it does

Feeling inside the upper larynx and the cricothyroid muscle (high notes).

Key facts

Roots: Vagus (inferior ganglion); internal and external branches
Moves: Cricothyroid (external branch)
Feeling from: Larynx above the vocal folds (internal branch: cough reflex)

Relations

Course: Leaves the inferior (nodose) ganglion of the vagus nerve, runs down and forward on the side of the pharynx deep to the internal carotid artery, and divides near the greater horn of the hyoid bone into its two branches
Lateral: Internal and external carotid arteries, which lie superficial to it
Medial: Middle and inferior pharyngeal constrictors
Below: The internal branch enters the larynx through the thyrohyoid membrane and runs under the mucosa of the piriform fossa; the external branch reaches the cricothyroid near the upper pole of the thyroid gland

How to find it

The internal branch is targeted in a superior laryngeal nerve block just below the greater horn of the hyoid bone, where it pierces the thyrohyoid membrane; it can also be numbed from inside through the mucosa of the piriform fossa. In thyroid surgery the external branch is looked for on the inferior constrictor, medial to the upper pole vessels.

Examination

Laryngeal adductor reflex on flexible endoscopy: a light touch or air pulse on the aryepiglottic fold normally closes the vocal folds briefly; a weak or absent response points to loss of internal branch sensation

On imaging

Not usually seen as a nerve. For a block, ultrasound finds its internal branch region beside the greater horn of the hyoid, over the thyrohyoid membrane, with the superior laryngeal artery on Doppler as a guide. After an injury the main test is laryngoscopy, not imaging; CT or MRI of the neck from the skull base to the larynx looks for a mass along its path.

Clinical notes

Cernea types describe where the external branch crosses the superior thyroid vessels; the type that crosses below the upper edge of the gland (2b) is the most exposed
Bilateral superior laryngeal nerve blocks, with topical or transtracheal anaesthesia, numb the airway for awake fibreoptic intubation
A high vagal lesion injures the superior and recurrent laryngeal nerves together: hoarse voice plus a numb larynx, with a greater risk of aspiration than a recurrent nerve lesion alone
Superior laryngeal neuralgia: brief stabbing pain in the side of the throat on swallowing, yawning or coughing, with a tender point over the thyrohyoid membrane

Anatomical variants

The internal branch often joins the recurrent laryngeal nerve inside the larynx (Galen anastomosis)
The external branch sometimes runs within the fibres of the inferior constrictor, which shields it during surgery
Its relation to the superior thyroid artery varies widely, which is why surgeons identify it rather than assume its position

Development

It is the nerve of the fourth pharyngeal arch, which is why its external branch supplies the cricothyroid, the only intrinsic laryngeal muscle outside the recurrent laryngeal nerve's territory.

Memory aid

External to the External muscle: the cricothyroid is the only intrinsic laryngeal muscle on the outside of the larynx; Internal goes Inside, for sensation.

Thyroid cancer (papillary)

Test yourself

Think of the answer, then tap the question to see it.

What does the internal branch of the superior laryngeal nerve supply, and how does it enter the larynx?

Sensation of the larynx above the vocal folds, epiglottis and piriform fossa; it pierces the thyrohyoid membrane with the superior laryngeal artery.

Which muscle does the external branch of the superior laryngeal nerve supply, and why is it at risk in thyroid surgery?

The cricothyroid, which tenses the vocal folds for high pitch; it runs beside the superior thyroid artery near the upper pole.

Why does loss of the internal branch of the superior laryngeal nerve risk aspiration?

It removes the cough and protective closure reflexes above the glottis, so food and saliva can be aspirated silently.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): nervus laryngeus superior TA2 6339
Official Spanish (DeCS): Nervio laríngeo superior DeCS D007823
English (TA2): Superior laryngeal nerve
Also called: nervus laryngicus cranialis

Cricothyroid

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Head and Neck: Laryngeal Nerves; Anatomy, Head and Neck: Larynx.

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Representative model, for educational purposes only.