K1i / 23B20: Outline the anatomy (60% marks) and synaptic physiology (40% marks) of the Vagus Nerve

23B20: Exam Report

Outline the anatomy (60% marks) and synaptic physiology (40% marks) of the Vagus Nerve

25% of candidates passed this question.

The vagus nerve anatomy was best broken down into a description of the fibers it carries (visceral, parasympathetic and somatic sensory fibres) and then origin and course from the parasympathetic, sensory and motor nuclei in the medulla as the tenth cranial nerve to its branches; the pharyngeal, cardiac, pulmonary and laryngeal branches.

Pre and post-ganglionic physiology involved a detailed description of the Muscarinic Ach receptor and events.

This would also include the 5 subtypes of the muscarinic receptor, with the locations and downstream effects of the M1-M3 locations being the most important to note.

K1i / 23B20: Outline the anatomy (60% marks) and synaptic physiology (40% marks) of the Vagus Nerve



  • Within medulla oblongata of brainstem: 4 vagal nuclei


  • Exits from medulla oblongata -> the nerves emerge by a series of rootlets in retroolivary groove between the olive and the inferior cerebellar peduncle -> travels laterally exiting skull through jugular foramen
  • Passes down the neck between carotid artery and internal jugular vein within carotid sheath -> enters thorax at base of neck
  • Left vagus nerve travels anterior to aortic arch, behind primary left bronchus -> through esophageal hiatus of diaphragm into abdomen
  • Right vagus nerve travels behind esophagus and primary right bronchus -> through esophageal hiatus of diaphragm into abdomen


  • Dorsal Nucleus: parasympathetic fibres to intestines
  • Nucleus ambiguus: efferent motor and parasympathetic fibers to the heart
  • Solitary nucleus: receives special gustatory afferent from tongue and visceral afferent fibers from organs
  • Spinal trigeminal nucleus: receives general sensory afferent fibers


  • Branches in jugular fossa
    • Meningeal branch
    • Auricular branch
  • Branches in neck
    • Pharyngeal nerve
    • Superior laryngeal nerve: internal and external laryngeal branches
    • Recurrent laryngeal nerve: innervates all other intrinsic laryngeal muscles except cricothyroid muscle
      • Right: travels under subclavian artery
      • Left: loops around aortic arch distal to ligamentum arteriosus
    • Superior cardiac branches
  • Branches in the thorax
    • Inferior cardiac nerve
    • Anterior & posterior bronchial branches
    • Esophageal branches
  • Branches in the abdomen
    • Gastric branches
    • Celiac branches
    • Hepatic branches


  • General afferent (sensory) fibers
  • Special sensory fibers
  • Visceral afferent (sensory) fibers
  • Branchial efferent (motor) fibers
  • Visceral efferent (motor) fibers

Presynaptic physiology

  • Presynaptic terminals release acetylcholine, postsynaptic membrane carries N2 nicotinic receptors

Postsynaptic physiology

    • Muscarinic receptors




  • CNS: ↑cognitive function, ↑seizure activity
  • Gastric parietal cell → gastric acid secretion




  • Heart (SA node & AV node) → negative chronotropy
  • Bronchial SM → bronchoconstriction
  • Pupils: miosis (contraction of pupillary sphincter), contraction of ciliary muscle → far vision
  • CNS
  • GIT: stimulate gastric secretion, relax gastric/intestinal sphincters, contraction of gallbladder, ↑motility of stomach/intestine




  • CNS
  • Glandular tissue (lacrimal, salivary, GI, GU, respiratory & sweat glands) → ↑secretions
  • Bronchial SM → bronchoconstriction
  • Vascular SM → vasodilation (via NO release)
  • GI & GU SM contraction of walls; relaxation of sphincters; stimulate gastric/pancreatic secretion
  • Uterine contraction
  • Penile erection
  • Iris & ciliary muscle contraction
  • Secretion of sweat glands




  • Inhibition of neurotransmitter release in CNS
  • Facilitates dopamine release




  • Facilitates dopamine release

Author: Novia Tan