Innervation of the vocal cords

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The vocal cords are innervated by the superior laryngeal nerve and the recurrent laryngeal nerves which are branches of the vagus nerve (cranial nerve X).

The superior laryngeal nerve splits into the external and internal branches. The internal branch contains sensory nerves from the larynx whereas the external branch supplies the cricothyroid muscle which tenses the vocal cords.


Damage to the superior laryngeal nerves can be caused by thyroid surgery.
Unilateral damage to the superior laryngeal nerve causes slight voice changes, usually affecting pitch.
Bilateral damage to the superior laryngeal nerves reduces the ability for the vocal cords to close increasing the risk of aspiration.

The recurrent laryngeal nerves supply the other muscles of the vocal cords, including the posterior cricoarytenoid muscle which is the only muscle which opens the vocal cords. The recurrent laryngeal nerves have a different course on the left and the right. The left is longer and descends down to the aortic arch and runs under it and up back to the larynx. It is more prone to surgical trauma especially in mediastinal surgery, oesophageal surgery and surgery involving the aorta. The right nerve hooks around the right subclavian artery.


Unilateral damage to the recurrent laryngeal nerves causes hoarseness.
Bilateral damage to the recurrent laryngeal nerves can comprimise the airway as the posterior criocoarytenoids cannot open them.


http://www.drtbalu.com/vc_palsy.html
http://emedicine.medscape.com/article/1923100-overview

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