Course of facial nerve and branches

Localization of site of lesion

• Upper motor neurone:
  Lower two thirds of the face is controlled by the contralateral motor cortex only.
  Forehead is controlled by both contralateral and ipsilateral cortex.
  In upper motor lesion the forehead moves normally while the contralateral lower two thirds of face is weak.
• Lower motor neurone:
  Entire ipsilateral face is weak. Location of lesion is determined by the associated involvement of other local structures.
  • Pontine location: Lateral rectus weakness (VI cranial nerve)
  • Cerebellopontine angle location: Ipsilateral deafness (VIII cranial nerve), hyperacusis, loss of taste over anterior third of tongue.
  • Facial canal: Depends whether the branch to stapedius and chorda tympani are involved. Ipsilateral hyperacusis and loss of taste over anterior two thirds of tongue.
  • Stylomastoid foramen: Bells palsy.

Diseases causing damage to facial nerve

• Cortical lesion
• Pontine hemorrhage
• Acoustic neuroma
• Trauma to temporal bone
• Non-specific inflammation of facial nerve
• Herpes zoster
• Sarcoidosis
• Parotid malignancy

Ref:

1. Castro, Mosby's....Neuroscience,157-160.
2. Review Dr. McNulty's lesson, "Master Muscle List".
3. Review Dr. McNulty's lesson, "Face lecture".