Vagus nerve (CN X)

Overview

Location

Medulla → jugular foramen → carotid sheath in the neck → posterior mediastinum (behind the lung roots, on the oesophagus) → oesophageal hiatus → abdomen.

Parts & subdivisions

1. Functional components
   Both (mixed): SVE, GVE, GVA, SVA and GSA. ≈80% of fibres are afferent, which is why vagal afferents dominate visceral reflexes such as the baroreflex, the Hering–Breuer reflex, satiety and nausea.
2. Recurrent laryngeal nerve asymmetry
   The right RLN loops around the right subclavian artery, a remnant of the 4th arch. The left RLN loops around the aortic arch next to the ligamentum arteriosum (6th arch). Because the left nerve is longer and runs through the mediastinum, it is more vulnerable, for example to a lung tumour at the left hilum, an aortic arch aneurysm or an enlarged left atrium (Ortner syndrome).
3. Clinical testing
   Ask the patient to say "aah" and watch the palate and uvula. With a unilateral lesion the palate fails to rise on the affected side and the uvula deviates toward the intact (opposite) side. Also assess the voice (hoarseness, a "bovine" cough), swallowing, the gag reflex (efferent limb) and the cough.
4. Lesion signs
   Ipsilateral palatal droop with the uvula deviated away from the lesion, nasal speech and regurgitation, dysphagia, hoarseness from vocal fold paralysis, a weak cough, and a loss of the gag reflex efferent limb.

Anatomy

Innervation

- Motor: pharyngeal constrictors, palatopharyngeus, salpingopharyngeus, levator veli palatini, musculus uvulae, palatoglossus (the only tongue muscle not supplied by XII), and all intrinsic laryngeal muscles.
• Parasympathetic: heart (SA and AV nodes), bronchial smooth muscle and glands, and the gut and its glands as far as the left colic flexure.
• Sensory: external ear and tympanic membrane, dura of the posterior fossa, the laryngopharynx and larynx, and thoracoabdominal visceral afferents, including the aortic arch baroreceptors and aortic bodies.
• Taste: epiglottis and root of the tongue.

Course

Postolivary sulcus → jugular foramen (superior and inferior ganglia) → carotid sheath → root of the neck. On the right it passes anterior to the subclavian artery (giving the right RLN); on the left it runs between the left common carotid and subclavian arteries, across the aortic arch (giving the left RLN). Each vagus then passes posterior to the lung root, forms the oesophageal plexus, and becomes the anterior and posterior vagal trunks → through the oesophageal hiatus (T10) → coeliac, hepatic and gastric branches → midgut.

Branches

- Auricular branch (Arnold nerve): skin of the external acoustic meatus and the back of the auricle.
• Pharyngeal branch: the motor part of the pharyngeal plexus.
• Superior laryngeal nerve, with two divisions:
- the internal division pierces the thyrohyoid membrane and carries sensation from the larynx above the vocal folds; it is the afferent limb of the cough reflex;
- the external division supplies cricothyroid.
• Recurrent laryngeal nerves: all intrinsic laryngeal muscles except cricothyroid, sensation below the vocal folds, and branches to the upper oesophagus and trachea.
• Cardiac branches (cardiac plexus), pulmonary branches (pulmonary plexus), the oesophageal plexus, and the anterior and posterior vagal trunks (gastric, hepatic, coeliac and renal branches).

Function

• Swallowing (pharyngeal phase) and elevation of the soft palate
• Phonation and protection of the airway (laryngeal muscles; cough reflex)
• Slowing of the heart rate (parasympathetic to the SA/AV nodes, M2 receptors)
• Bronchoconstriction and airway secretion
• Gut motility and secretion (gastric acid, pancreatic juice) to the left colic flexure
• Visceral afferent input for the baroreflex, chemoreflex, satiety, nausea and the gut–brain axis

Clinical significance

Mnemonics

Related structures