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Facial Nerve

s- VII

Summary

  1. Somatic Afferents
    • External auditory meatus
    • Auricle – Posterior auricular nerve
  2. Special Afferents
    • Taste to anterior 2/3 tongue
  3. Visceral Efferents
    • Lacrimal Gland
    • Submandibular Gland
    • Sublingual gland
  4. Somatic Efferents
    • Muscles of Facial expression
    • Stylohyoid
    • Stapedius
    • Posterior belly of Digastric

Origin

  • Main Facial Nerve: Lower border of the Pons above the Olive
  • Nervus Intermedius: Between pons and Inferior Cerebellar Peduncle – near the Vestibulocochlear Nerve

Course

  • Arises in the pons with a motor and a sensory root
  • Enter Internal Acoustic Meatus
    • Near the Middle Ear, the nerve makes a sharp posterior bend (the Geniculum)
      • Enlarged by the cell bodies of the Afferent taste fibres to form the Geniculate Ganglion
    • Nerve runs back in the medial wall of the Middle Ear
  • Passes vertically down the Facial Canal
    • Branches of Facial Nerve within Petrous Bone:
      • Greater Petrosal Nerve
      • Nerve to Stapedius
      • Chorda Tympani
        • Consists of Nervus Intermedius Fibres
        • Leaves Facial nerve in Facial Canal 6mm above Stylomastoid Foramen
        • Passes through Posterior Wall of Middle Ear
        • Joins the Lingual Nerve in the Infratemporal Fossa
        • Taste fibres taken to the anterior part of the tongue
        • Secretomotor fibres relay in the Submandibular Ganglion for the Submandibular Gland
  • Emerges from the Stylomastoid Foramen
    • Near origin of the Posterior Belly of Digastric
    • Immediately gives off Posterior Auricular Nerve
      • Passes upwards behind the ear to supply Auricularis Posterior and Occipital Belly of Occipitofrontalis
    • Muscular Branch next given off which divides to supply
      • Posterior Belly of Digastric
      • Stylohyoid muscles
  • Nerve approaches posteromedial surface of Parotid Gland
    • Just before entering or within the gland, it divides into an upper Temporofacial and a lower Cervicofacial division
    • Within substance of Parotid Gland, each division divides and rejoins to divide again and finally emerge from the Parotid Gland in 5 main groups of branches
      • Pes anserinus (this plexiform arrangement) lies in the gland superficial to the Retromandibular Vein and the External Carotid Artery
    • Branches emerge from behind the anterior border of the gland
      • No branches emerge from the superficial aspect of the gland

Muscular branches

Temporal Branches

  • Emerge from upper border of gland
  • Lies in front of Superficial Temporal Artery
  • Cross Zygomatic Arch
  • Supply:
    • Auricularis anterior and superior
    • Part of Frontalis
  • Action:
    • Wrinkling forehead
  • Consequence of injury: Brow asymmetry and brow ptosis, inability to wrinkle forehead

Zygomatic Branches

  • Cross the Zygomatic Arch and Zygomatic Bone
    • Lies directly on the periosteum
  • May be damaged in fractures or operations in this region
  • Supply:
    • Obicularis Oculi
  • Action:
    • Blinking of the eye allowing precorneal film of tears to be spread
  • If damaged, precorneal film of tears no longer spread ⇒ Dry cornea ulcerates ⇒ Resultant scar impairs vision
    • The most serious consequence of impaired Facial Nerve Function

Buccal Branches

  • Run forwards close to the Parotid Duct in parallel
  • Often one above and one below the Duct
  • Supply:
    • Buccinator
    • Muscle fibres of the Nose
    • Muscle fibres of Upper Lip
  • Action:
    • Emptying of the cheek pouch
  • If damaged, bolus lodges in cheek pouch and cannot be returned to molar teeth
    • Chewing has to be performed on the other side

Marginal Mandibular Branch

  • Frequently single
  • Runs forwards above, along or below the lower border of the Mandible
  • From below Mandible, it crosses the inferior border of the bone to reach the face just beyond the anterior border of the Masseter
  • Passes superficial to the Facial Artery and Facial Vein
    • Small node lies here
  • Deep to platysma
  • Nerve in danger when an incision is made at or near the lower border of the Mandible
  • Nerve does not communicate with a Buccal Branch
  • Supplies:
    • Depressors of the Lower Lip and Mouth Angle
  • If damaged, detectable paralysis of the depressors will be seen – asymmetry of the mouth when speaking or smiling

Cervical Branch

  • Passes downwards from the lower border of the Parotid Gland
  • Supplies Platysma
  • Consequence of injury: Asymmetry of the motion of the corner of the mouth

Identification of Facial Nerve During Parotid Surgery

  • Main trunk emerges from Stylomastoid Foramen
  • Winds lateral to the Styloid Process just above the tendon of the Stylohyoid Muscle
  • Relationship of Stylomastoid Foramen and the Tympano-mastoid Fissure useful landmark
    • Main trunk < 1cm deep to Tympano-mastoid suture line at the level of the Digastric Muscle
  • Facial Nerve approached along a plane in front of the anterior margin of the cartilage
    • Just deep to the junction of the cartilaginous and bony parts of the External Meatus
    • Cartilage in this region has an arrow-headed projection pointing downwards to the nerve trunk
    • a.k.a. Tragal Pointer of Conley

  • About 1cm above and medial to the upper end of the Posterior Belly of Digastric
  • Stylomastoid branch of Posterior Auricular Artery is superficial to the Facial Nerve and is a guide to its proximity
  • Alternative approach: find a Facial Nerve Branch as it leaves the gland and follow it in a centripetal manner back to the Trunk and other branches
    • Marginal Mandibular Branch may be identified as it lies superficial to the Retromandibular Vein or its Anterior branch – aided by the colour contrast between the white nerve and the dark vein
    • Occasionally, this nerve will pass behind the vein
  • Alternatively, the Cervical Branch may be followed up from its communication with the Ascending Branch of the Transverse Cervical Nerve

Graph View

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