THE VAGUS NERVE (CN X)

 


The Origin(s), Functional components and Distribution

Nucleus
Components
Distribution

Dorsal vagal nucleus: pre-ganglionic parasympathetic (GVE)
  • Mucous glands of the larynx
  • Visceral contents of the entire thorax and most of the abdomen.
Nucleus ambiguus: Motor neurons (SVE)
  • Muscles of the pharynx and of the larynx, except the stylopharyngeus (glossopharyngeal) and tensor veli palatini (trigeminal) muscles.
Nucleus tractus solitarius: sensory (GVA)

Fibres from the mucosal linings of the:

  • pharynx
  • larynx,
  • soft palate.
dorsal sensory nucleus GVA
  • Carotid sinus
The spinal nucleus of CN V: General sensory (GSA) fibres.
  • Pinna of the ear
  • External auditory meatus
  • Meninges
Gustatory nucleus: Special visceral affarent ( SVA)
  • Taste fibres from the epiglottis.


The Course

  • Emerges from the brain stem as a series of rootlets just dorsal to the inferior olive.

  • Passes caudal to the glossopharyngeal nerve and rostral to the spinal accessory nerve.

  • Exits through the jugular foramen.

  • Initially courses with the spinal accessory nerve

  • Has two sensory ganglia: superior (jugular) ganglion (GSA) and inferior (nodose) ganglion (SVA and GSA)

  • Descends in the neck, within the carotid sheath ,

  • Posterior and between internal carotid and common carotid arteries and internal jugular vein.

  • Remains in the carotid sheath until it enters the thoracic cavity.

 

 

 


Branches and Distribution  
 
Branch
Distribution
Auricular nerve
  • Pinna
  • External auditory meatus.

meningeal nerve

  • Dura of the posterior cranial fossa.
Pharyngeal nerves
  • Muscles of the pharynx and soft palate except the stylopharyngeus and tensor veli palatini muscles

  • GVE pre-ganglionic parasympathetic innervation to glands in the pharyngeal mucosa.

superior laryngeal nerve:two branches

a) internal laryngeal nerve

  • Sensory innervation (GVA) to the mucosa of the larynx down to the level of the vocal cords
b) external laryngeal nerve
  • Inferior pharyngeal constrictor and Cricothyroid muscles
Recurrent laryngeal nerve
  • Intrinsic muscles of the larynx (SVE), except the cricothyroid muscle.

  • Laryngeal mucosa below the vocal cords,
  • Trachea
  • Oesophagus.

 

Clinical Disorders of vagus nerve

The vagus nerve can be injured by :

  • Expanding CP angle lesions;
  • Hydrocephalus;
  • Cerebellar tumors or meningiomas
  • Aneursyms of carotid arteries
  • Neck surgery
  • Brain stem vascular lesions e.g. PICA syndrome
  • Other brain stem lesions e.g. amyotrophic lateral sclerosis, poliomyelitis, and brain stem tumors

This leads to:

  • Persistent hoarseness in the voice

  • Drooping of the soft palate on the affected side

  • Deviation of the uvula away from the injured side

  • Dysphagia with food passing into the nasopharynx and trachea

  • Loss of gag reflex
  • Hyperacidity and Gastric ulceration.

 

Damage only to the recurrent laryngeal nerve may occur during:

  • Thyroid surgery
  • Tracheostomy
  • Oesophageal surgery
  • Tracheobronchial lymph node enlargement
  • Bronchogenic carcinoma
  • Esophageal carcinoma

The GSA neurons in the vagus nerve form the auricular nerve to the external auditory meatus, which makes reflex connections with the dorsal motor nucleus of the vagus. Thus, stimulation of the external ear can cause coughing, nausea and even fainting.