Facial Nerve (CNVII)

Summary

  • Function
  • Structure
    • Nuclei
    • Course
      • Intracranial
      • Extracranial
  • Summary

Function

  • CNVII contains 3 types of fibres:
    1. GSE  to structures derived from the 2nd pharyngeal arch
      1. Muscles of facial expression
      2. Stapedius
      3. Stylohyoid
      4. Posterior belly of digastric
    2. GVE to the lacrimal, submandibular, sublingual  and glands in nose and palate
      1. I.e. parasympathetic supply to glands
    3. SVA – taste from the anterior 2/3 tongue
    • NB No GVA function to the face ( this is taken by CNV)

Course

Nuclei
  • Engages with 3 nuclei :
    1. Facial motor nucleus (GSE) in the pons
    2.  Superior salivatory nucleus (parasympathetic – GVE/GVA) in the pons
    3. (terminates in) Nucleus tractus solitarius (taste/SVA) in the medulla and also involves CNIX and CNX
Note the location of the three nuclei of CNVII (facial motor nucleus, superior salivatory nucleus, nucleus solitarius)
  • Joins/leaves the brainstem  near the pontomedullary junction (region known as cerebellopontine angle)
    • CNVIII also enters  here

Course
  • The path of the facial nerve can be divided into six segments. (In My Lifetime, Teslas May Explode)
    1. Intracranial (cisternal) segment
    2. Meatal segment (brainstem to internal auditory canal)
    3. Labyrinthine segment (internal auditory canal to geniculate ganglion)
    4. Tympanic segment (from geniculate ganglion to pyramidal eminence)
    5. Mastoid segment (from pyramidal eminence to stylomastoid foramen)
    6. Extratemporal segment (from stylomastoid foramen to post parotid branches)

  • Intracranial segment
    • The three parts of the nerve arise
  • Meatal segment
    • The three parts merge
    • Traverse the posterior cranial fossa and enter the facial canal within the petrous part of the temporal bone via the internal acoustic meatus
  • Labyrinthine segment
    • Bends posteriorly to form geniculate ganglion within the canal (number 4)
      • Gives off the greater petrosal nerve to the pterygopalatine ganglion
  • Tympanic segment
    • Passes across the tympanic cavity
  • Pyramidal eminence/mastoid segment
    • Takes sharp downward turn to descend almost vertically and gives off ‘nerve to stapedius‘ and chorda tympani
  • Extracranial portion (see separately below for more detail)
    • Leaves skull through stylomastoid foramen
    • Passes through the parotid gland to form the parotid plexus – gives off terminal branches

      Passage of CNVII through the facial canal
    • 3 key important branches within the intracranial course
      1. Greater petrosal nerve 
        • Given off at geniculate ganglion, pre-ganglionic parasympathetic fibres to the pterygopalatine ganglion which supplies the lacrimal gland/nose mucosa
      2. Nerve to stapedius
      3. Chorda tympani branch: this is a SVE/SVA nerve
        • Supplies tongue, submandibular, and sublingual glands
        • Comes off just before exiting the facial canal through the stylomastoid foramen. Ascends back up through temporal bone, enter middle and inner ear, passes  across the TM and descends toward the TMJ where it joins the lingual nerve (CNV branch).
        • Thus provides taste sensation to the tongue
Extracranial course of CNVII
  • NB extracranial CNVII gives off 3 branches before the plexus
    1. Posterior auricular nerve – supplies scalp around the ear
    2. Branch to (posterior) digastric
    3. Branch to stylohyoid
  • There are 5 branches of the facial nerve from the parotid plexus in the parotid gland (NB do not supply the parotid or other glands):
    1. Temporal
      • Auricularis superior + anterior
      • Occipitofrontalis (frontal aspect)
      • Superior part of orbicularis oculi – key
    2. Zygomatic
      • Mainly supplies muscles just inferior to the orbit – inferior orbicularis oculi
    3. Buccal – supplies upper lip muscles
      • Buccinator
      • Upper orbicularis oris
    4. Marginal Mandibular – supplies lower lip muscles
      • Lower orbicularis oris
      • Risorius
    5. Cervical
      • Supplies platysma
  • Remember these as Ten Zulus Bought My Cat
Extracranial branches of CNVII.
  • Note that each contains different types of fibres:
  • There is an overlap between the muscles innervated by each branch

Summary

Summary diagram showing the nuclei of CNVII and the structures they supply through different types of fibres.

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