Vagus nerve

Special sensory function

Carries taste fibers from epiglottis.

Sensory function

Innervates the skin of the external acoustic meatus. Also carries sensory fibers from lower pharynx and larynx.

Mediates some sensory information from dura.

Motor function

Motor innervation of soft palate (except tensor veli palatini), pharyngeal and laryngeal muscles.

Visceral innervation

Carries parasympathetic and sympathetic afferents mediating visceral sensory signals from cervical, thoracic and abdominal viscera.

Carries parasympathetic efferents that modulate heart, lung and digestive tract functions.

Anatomy

1. Intra-axial segment

All vagus associated nuclei are located in the upper and middle medulla oblongata.

Nucleus ambiguus is the origin of motor fibers innervating pharyngeal and laryngeal muscles.

Solitary tract nucleus is the destination of taste fibers from epiglottis.

The afferent component of dorsal nucleus of vagus nerve is the destination of visceral sensory fibers.

The efferent compoenent of dorsal nucleus of vagus nerve is the origin ofparasympathetic efferent visceral fibers to viscera.

The spinal trigeminal nucleus is the destination of sensory fibers from meninges and skin of externa acoustic meatus.

2. Cisternal segment

The nerve emerges from the lateral medulla in the postolivary sulcus, between the glossopharyngeal nerve and the accessory nerve. It courses through the basal cistern together with glossopharyngeal and accessory nerves.

3. Skull base segment

It runs through the posterior part (pars vascularis) portion of the jugular foramen, together with the accessory nerve and the jugular bulb. The superior vagal ganglion lies within the jugular foramen.

Within the jugular foramen, the auricular branch (Arnold’s nerve) arises from the superior vagal ganglion. It passes through the mastoid canaliculus and enters the external auditory canal through the tympanomastoid fissure. It provides sensory innervation to the outer tympanic surface and skin of external auditory canal and auricle.

4. Extracranial segment

Distal to the jugular foramen, vagus nerve enters the carotid space. The inferior vagal ganglion lies just below the skull base.

The superior laryngeal nerve arises from the inferior vagal ganglion and receives branches from the superior cervical ganglion (sympathetic nervous system). It innervates the cricothyroid muscle.

The pharyngeal branches arise just below the skull base. They provide motor innervation to pharyngeal muscles and soft palate (except tensor veli palatini which is innervated by the mandibular branch of trigeminus) and sensory innervation to epiglottis and cervical viscera.

Vagus then courses posterolateral to the internal carotid and common carotid artery and enters the thorax. In the superior mediastinum, the recurrent laryngeal nerves arise from the vagal trunks.

The left recurrent laryngeal nerve loops under the aortic arch. The right recurrent laryngeal nerve loops under the right subclavian artery. The recurrent laryngeal nerves course cranially and innervate all laryngeal muscles except the cricothyroid muscle (superior laryngeal nerve). They also provide sensory innervation to the mucosa of infraglottis.

In the thorax, the vagus nerves form pulmonary and esophageal plexuses from which branches to the heart, lungs, esophagus and stomach emerge. They then enter the abdominal cavity. Parasympathetic nerve fibers to abdominal organs follow the course of the blood vessels to those organs.

Clinical implications

• Proximal injury (between the medulla and the hyoid bone) causes pharyngeal and laryngeal dysfunction. It usually is associated with multiple cranial neuropathy involving the lower (9-12) cranial nerves.
• Distal injury (below hyoid bone) presents with laryngeal dysfunction and is usually isolated.
• Causes of vagus nerve palsy include iatrogenic injury, skull base tumors, stroke, processes affecting the jugular foramen.