Origin The superior laryngeal nerve arises from the middle of the
inferior ganglion of vagus nerve.
Course The superior laryngeal nerve descends by the side of the
pharynx deep to the
internal carotid artery before dividing into two branches —the external laryngeal nerve and the internal laryngeal nerve.''''''
Branches External laryngeal nerve The external laryngeal nerve is the smaller, external branch. It descends on the
larynx, beneath the
sternothyroid muscle, to supply the
cricothyroid muscle. The external branch functions to stretch the vocal cords by activating the cricothyroid muscle, increasing pitch. The external laryngeal nerve gives branches to
pharyngeal plexus and the superior portion of the
inferior pharyngeal constrictor, and communicates with the
superior cardiac nerve behind the
common carotid artery.
Internal laryngeal nerve The internal laryngeal nerve is the internal branch. It descends to the
thyrohyoid membrane, piercing it in company with the superior laryngeal artery, and is distributed to the
mucous membrane of the larynx. Of these sensory branches, some are distributed to the
epiglottis, the base of the
tongue, and the epiglottic glands; others pass posteriorly, in the
aryepiglottic fold, to supply the mucous membrane surrounding the entrance of the larynx, and the mucous lining of the larynx as far down as the vocal folds. A filament descends beneath the mucous membrane on the inner surface of the
thyroid cartilage and joins the
recurrent laryngeal nerve. Above the vocal folds the sensory innervation of the larynx is via the internal laryngeal nerve. Below the vocal folds it is by way of branches of the recurrent laryngeal nerve. The vocal fold itself receives dual innervation from both nerves. == Function ==