Facial Nucleus — Function, Location & Quiz

The facial nucleus contains the lower motor neurons that drive facial expression, but it receives more than one kind of command. Voluntary movement descends from cortex, while spontaneous emotional expression reaches it through a partly separate subcortical route.

Forehead innervation is the localization clue. The upper face receives bilateral cortical input, so a unilateral cortical stroke tends to spare forehead movement; a peripheral facial lesion affects the upper and lower face together on the same side.

Test this anatomy in the Lesion Localization Quiz or open the interactive 3D brain model.

Location and anatomical map

Lower motor neurons for facial muscles in the pons; damage causes Bell's palsy.

Atlas category: brainstem.

Functions

  • Lower motor neurons for facial muscles
  • Receives TWO separate pathways: voluntary (cortical) and emotional (subcortical)
  • Upper face: bilateral cortical innervation. Lower face: contralateral only

Pathways and connections

  • Motor cortex → Facial nucleus (voluntary pathway — contralateral for lower face, bilateral for upper face)
  • Premotor/BG → Facial nucleus via hypothalamus/brainstem (emotional pathway — spontaneous expressions)

Clinical relevance

  • Bell's palsy (peripheral lesion): complete unilateral facial paralysis — upper AND lower face
  • Cortical lesion (UMN): only contralateral LOWER face affected — forehead spared (bilateral innervation)
  • Double dissociation: voluntary pathway damage = can't smile on command but CAN smile spontaneously
  • Emotional pathway damage = CAN smile on command but CAN'T smile spontaneously

Key facts

  • Duchenne smile = genuine (zygomatic major + orbicularis oculi = crinkles eyes). Fake smile = zygomatic only
  • Upper face bilateral innervation explains why cortical stroke spares forehead but Bell's palsy does not
  • Double dissociation between voluntary and emotional facial pathways is a classic exam question

Exam tip

Upper face = bilateral control, lower face = contralateral only. This explains why cortical lesions spare the forehead but Bell's palsy doesn't.

Common questions

What does the facial nucleus control?

It provides lower-motor-neuron output to muscles of facial expression and receives separate descending influences for voluntary and spontaneous emotional movement.

Why is the forehead spared in many cortical strokes?

Upper-face motor neurons receive bilateral cortical input, so the intact hemisphere can still drive the forehead. Lower-face input is predominantly contralateral.

How does Bell’s palsy differ from a cortical facial weakness?

Bell’s palsy is a peripheral lesion causing ipsilateral upper- and lower-face paralysis. A unilateral cortical lesion usually weakens only the contralateral lower face.