Facial Nerve (Cranial Nerve VII) Notes

Facial Nerve Overview

  • Facial Nerve (Cranial Nerve VII)
    • Type: Mixed Nerve
    • Functions:
    • General Somatic Afferent (Sensory):
      • Touch, pain, temperature
    • Special Visceral Afferent (Sensory):
      • Smell, taste, vision, hearing, balance
    • General Visceral Efferent (Motor):
      • Secretion of glands
    • Branchial Efferent (Motor):
      • Muscles

Nuclei of the Facial Nerve

  • Main Motor Nuclei:

    • Located in reticular formation of lower pons
    • Voluntary Control:
    • Upper Facial Muscles:
      • Receive signals from both hemispheres
    • Lower Facial Muscles:
      • Receive signals from the contralateral hemisphere

  • Parasympathetic Nuclei:

    • Located posterolateral to main motor nuclei in the pons
    • Superior Salivatory Nucleus:
    • Target: Submandibular & sublingual glands
    • Function: Receives efferent fibers from hypothalamus (saliva production)
    • Lacrimal Nucleus:
    • Target: Lacrimal gland
    • Function: Receives afferent fibers from hypothalamus (crying)

  • Sensory Nucleus (Tractus Solitarius):

    • Located in medulla oblongata
    • Function: Processes taste sensation

Anatomical Course of the Facial Nerve

  • 3 Parts:

    1. Intracranial Segment:
    • Passes through cranial cavity from the ventrolateral aspect of caudal pons
    • 2 Roots:
      • Motor root: Carries Branchial Efferent (BE) fibers
      • Sensory root: Carries General Somatic Afferent (GSA), Special Afferent (SA), and General Visceral Efferent (GVE) fibers
    • Roots emerge separate at cerebropontine angle
    1. Infratemporal Segment:
    • Enters the internal acoustic meatus of the petrous part of the temporal bone
    1. Meatal Segment:
    • Enters IAM alongside vestibulocochlear nerve and labyrinthine artery
    • Note: Nerve lacks endoneurium

  • Labyrinthine Segment:

    • Shortest and narrowest segment from fundus of IAM to geniculate ganglion
    • Lacks strong blood supply

  • First Genu:

    • Sharp posterior and lateral bend at the geniculate ganglion

  • Tympanic Segment:

    • Nerve curves posteriorly around the oval window niche
    • Located anterior and inferior to lateral semicircular canal

  • Mastoid Segment:

    • Longest segment within the petrous bone

Terminal Branches of the Facial Nerve

  • 5 Terminal Branches:

    1. Temporal Branch:
    • Innervates:
      • Frontal belly of occipitofrontalis
      • Corrugator supercilii
      • Auricular muscles
    1. Zygomatic Branch:
    • Innervates:
      • Orbicularis oculi (closes the eye)
    1. Buccal Branch:
    • Innervates:
      • Orbicularis oris (closes lips)
      • Zygomaticus minor/major (pulls corners of lips up)
    1. Mandibular Branch:
    • Innervates:
      • Orbicularis oris (closes lips)
      • Buccinator (compresses cheeks)
    1. Cervical Branch:
    • Innervates:
      • Platysma (pull corners of mouth down/frown)