Neurosurgery notes/Anatomy/Cranial nerves/CN 9

CN 9

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Cranial nerves

Course

  • The glossopharyngeal nerve emerges from the medulla with the vagus and hypoglossal nerves and exits the skull via the jugular foramen, accompanied by the vagus and accessory nerves.
Jacobson nerve
  • Aka
    • Tympanic branch of the glossopharyngeal nerve (CN IX)
  • Inferior salivary nucleus → Arises from the inferior ganglion of the glossopharyngeal nerve → Carries preganglionic parasympathetic fibres → enters the tympanic cavity via the inferior tympanic canaliculus (Jacobson canal) → contributes to the tympanic plexus located on the cochlear promontory → The parasympathetic fibres leave the plexus as the lesser petrosal nerve → Otic ganglion → auriculotemporal nerve → parotid gland
  • Pathology
    • The neuroendocrine cells related to this nerve give rise to tympanic paraganglioma.
    • A Jacobson nerve schwannoma is a rare middle ear tumour presenting as a mass along the cochlear promontory or enlargement of the inferior tympanic canaliculus
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Tympanic nerve supplies the parasympathetic afferents of the tympanic plexus (see Nerve anastomosis)
Tympanic nerve supplies the parasympathetic afferents of the tympanic plexus (see Nerve anastomosis)
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Function

  • Five functional components make up the glossopharyngeal nerve (IX):
      • Components
      Ganglia
      Nuclei
      Exit through Skull
      Target Organ
      Function
      Somatic motor
      ㅤ
      Nucleus ambiguus
      Jugular foramen
      Stylopharyngeus
      Elevates pharynx
      Visceral motor
      Otic
      Inferior salivatory
      ㅤ
      Parotid gland
      Gland secretion
      Somatic sensory
      Superior glossopharyngeal
      Spinal trigeminal tract
      ㅤ
      External ear
      Somatic sensation
      Visceral sensory
      Inferior glossopharyngeal
      Solitary tract
      ㅤ
      Carotid sinus and body; pharynx and posterior third of tongue
      Baro- and chemoreceptor reflexes; pain, temperature, and touch sensation
      Special sense
      ㅤ
      ㅤ
      ㅤ
      Taste buds in posterior third of tongue
      Taste
    • Special sensory fibers have their cell bodies in the inferior glossopharyngeal ganglion.
      • They supply the taste buds in the posterior third of the tongue and terminate in the nucleus of the solitary tract.

Clinical

Hering’s nerve

  • A branch of CN IX that is the sensory limb of the carotid body. When a chemoreceptor detects changes in blood O2 and CO2 concentration, Hering’s nerve is stimulated

Glossopharyngeal nerve lesion

  • Rarely occurs in isolation
  • Causes
    • Hoarse voice
    • Dysphagia
    • Loss of the gag reflex
    • Glossopharyngeal neuralgia
      • A syndrome of agonizing ear and throat pain, is similar in character to trigeminal neuralgia but less common.

Relationship of CN9 with other nerves

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Images

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