Definition of Vagus nerve

Vagus nerve: A remarkable nerve that supplies nerve fibers to the pharynx (throat), larynx (voice box), trachea (windpipe), lungs, heart, esophagus, and the intestinal tract as far as the transverse portion of the colon. The vagus nerve also brings sensory information back to the brain from the ear, tongue, pharynx, and larynx.

The vagus nerve is the tenth cranial nerve. It originates in the medulla oblongata, a part of the brain stem, and wanders all the way down from the brainstem to the colon.

Complete interruption of the vagus nerve causes a characteristic syndrome. The back part of the palate (the soft palate) droops on that side. The capacity to gag (the gag reflex) is also lost on that side. The voice is hoarse and nasal. The vocal cord on the affected side is immobile. The result is dysphagia and dysphonia (trouble swallowing and trouble speaking).

One of the best known branches of the vagus nerve is the recurrent laryngeal nerve. After leaving the vagus nerve, the recurrent laryngeal nerve goes down into the chest and then loops back up to supply the larynx (the voice box). Damage to the recurrent laryngeal nerve can result from diseases inside the chest (intrathoracic diseases) such as a tumor or an aneurysm (ballooning) of the arch of the aorta or of the left atrium of the heart. The consequence is laryngeal palsy, paralysis of the larynx (the voice box), on the affected side. Laryngeal palsy can also be caused by damage to the vagus nerve before it gives off the recurrent laryngeal nerve.

The term "vagus" (Latin for "wandering") is apt because the vagus nerve wanders all the way down from the brainstem to the colon, a long wandering way.