The external and internal laryngeal nerves :difference between

 

The external and internal laryngeal nerves are branches of the superior laryngeal nerve which is the branch of  vagus nerve (CN X).

1. Location of these nerves

• External Laryngeal Nerve branch of superior laryngeal nerve
• Descends alongside the superior thyroid artery.
• It runs along the external surface of  the larynx, related to the the thyrohyoid membrane.
• It is supplied  the cricothyroid muscle.
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• Internal Laryngeal Nerve branch of superior laryngeal nerve
• The internal laryngeal nerve (internal branch of the superior laryngeal nerve) descends to the thyrohyoid membrane, piercing it alongside the superior laryngeal artery. It provides sensory innervation to the epiglottis, base of the tongue, epiglottic glands, aryepiglottic folds, and laryngeal mucosa down to the vocal folds.

2. Relation

• External Laryngeal Nerve : near to  the superior thyroid artery, which makes it vulnerable during thyroid surgery. It is situated outside the larynx, and related  to the inferior constrictor muscle.
• Internal Laryngeal Nerve : it is run with the superior laryngeal artery and pierce the thyrohyoid membrane. It is located deep to the laryngeal mucosa,  the aryepiglottic folds and epiglottis.
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3. Function

• External Laryngeal Nerve
• Motor function: Supplies the cricothyroid muscle, which tenses the vocal cords and modulates pitch of voice.
• Clinical significance: Damage of this nerve leads to a monotonous voice (no up or down of speech) due to loss of high-pitched sounds.
• Internal Laryngeal Nerve
• Sensory function: it gives sensation to the mucosa of the larynx above the vocal cords, including the epiglottis and piriform recess.
• Clinical significance: Damage of this nerve causes loss of cough reflex, leading to aspiration of food or fluid within the larynx.

 

Concise difference between external and internal laryngeal nerve

Feature	External Laryngeal Nerve	Internal Laryngeal Nerve
Origin	Superior laryngeal nerve (CN X)	Superior laryngeal nerve (CN X)
Course	Runs along the superior thyroid artery	Pierces the thyrohyoid membrane
Relation	It is closely related   to superior thyroid artery which is the branch of external carotid artery , outside larynx	It runs with  superior laryngeal artery which is the branch of superior thyroid artery ,  inside larynx
Function	Motor: innervate Cricothyroid muscle (pitch control)	Sensory: it gives sensory supply to the mucosa above vocal cords (cough reflex)
Damage Effect	No voice loss but monotonous voice (no high pitch)	Loss of sensation, risk of aspiration of food or fluid within the larynx