Facial Nerve Anatomy

Facial Nerve Anatomy

The facial nerve has intracranial, intratemporal and extracranial anatomical sections. This article details the origin, course, branches and variations of the facial nerve.

Summary Card


Overview
Cranial nerve VII is a motor and sensory nerve with intracranial, intratemporal and extratemporal anatomical sections.


Intracranial
Originates at the medullopontine angle of the brain stem from the facial nerve proper and nervus intermedius.


Intratemporal
The intratemporal facial nerve enters the internal auditory canal and provides motor, sensory and secretomotor branches.


Extracranial
Begins at the stylomastoid foramen, provides branches to nearby muscles, enters the parotid and divides into the 5 terminal branches.


Terminal Branches
Mnemonic: To Zanzibar By Motor Car: Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical.


Flashcards
Evidence-based flashcards to improve your active recall.


References
Peer-reviewed, evidence-based citations.


Overview of Facial Nerve Anatomy


Key Point

The facial nerve (cranial nerve VII) is a motor and sensory nerve that has 3 distinct intracranial, intratemporal and extratemporal anatomical sections.

The facial nerve (cranial nerve VII) is a motor and sensory nerve that has 3 distinct intracranial, intratemporal and extratemporal anatomical sections.

  1. Intracranial: arises from the precentral gyrus & travels via dorsolateral pons.
  2. Intratemporal: fallopian canal's labyrinthine, tympanic & mastoid segments.
  3. Extra-temporal: from stylomastoid foramen to 5 branches via the parotid.

These three sections of the facial nerve are visualised in the illustration below.

An illustrated diagram showing the facial nerve in yellow travel through its intracranial, extracranial and intratemporal anatomical sections
Facial Nerve Anatomy

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Fun Fact:  Ipsilateral supranuclear lesions cause contralateral facial paralysis with preserved frontalis because the temporal branch receives bicortical input (unlike other branches).


Intracranial Facial Nerve Anatomy


Key Point

The facial nerve arises from the medullopontine angle of the brain stem from the facial nerve proper (motor) and nervus intermedius (parasympathetic and sensory fibres).

Intracranial Facial Nerve Origin

The facial nerve is formed by the facial nerve proper and the nervous intermedius.

  1. Facial Nerve Proper: motor fibres exiting from the cerebellopontine angle.
  2. Nervus Intermedius: parasympathetic and sensory fibres.

Intracranial Facial Nerve Course

The intracranial section has 3 important anatomical landmarks:

  1. Arises from the medullopontine angle of the brain stem.
  2. Travels with cranial nerve VIII at the internal auditory meatus.  
  3. Enters the petrous temporal bone

This intracranial course of the facial nerve is visualised in the illustration below.

Intracranial Facial Nerve Anatomy


Intratemporal Facial Nerve Anatomy


Key Point

The intratemporal facial nerve enters the internal auditory canal, has 5 main segments and provides motor, sensory and secretomotor branches.


Intratemporal Facial Nerve Course  

  • Enters the internal auditory canal with the acoustic and vestibular nerves.
  • Travels the fallopian canal by itself through the segments.
  • Segments: cisternal, intracanlicular, labyrinthine, tympanic, mastoid

Intratemporal Facial Nerve Branches

These final two segments provide several branches that prove parasympathetic and taste innervation:

  • Tympanic: greater & external & lesser petrosal nerves
  • Mastoid: nerve to stapedius, sensory auricular, chorda tympani

Three clinically significant branches from this segment are:

  • Greater Petrosal: lacrimal gland & soft palate taste via geniculate ganglion.
  • Nerve to Stapedius: dampens loud noises (unaffected in Möbius Syndrome)
  • Chorda Tympani: salivary glands, anterior 2/3 tongue taste via lingual.

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Tip: intracranial facial nerve injury results in loss of taste (ageusia) to the anterior 2/3 tongue and hyperacusia (nerve to stapedius). 


Extracranial Facial Nerve Anatomy


Key Point

The extracranial facial nerve arises from the stylomastoid foramen, provides branches to nearby muscles, enters the parotid and divides into the 5 terminal branches.

Extracranial Facial Nerve Course

The facial nerve becomes extracranial after the stylomastoid foramen, where it is protected by the mastoid tip, tympanic ring, and mandibular ramus.  

It then travels past bone, muscle and cartilage before reaching the parotid gland.

  • Anterior to the posterior belly of the digastric muscle
  • Lateral to the styloid process of the temporal bone.
  • Inferomedially (~1cm3) to the tip of the tragal pointer of the ear
  • Posteriomedially enters the parotid gland
  • Forms temprozygomatic and cervicofacial trunks in the pes anserinus.
  • Divides into terminal branches that innervate facial muscles.

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Tip: Arborization begins in the parotid gland between the major terminal branches in the majority of patients. 

Extracranial Facial Nerve Branches

The facial nerve provides motor branches to the structures it passes by on its way to the parotid gland.

  • Postauricular nerve: occipitalis and posterior auricular muscles
  • Branch to the posterior belly of digastric and stylohyoid
  • Terminal branches: this is discussed in more detail below.  

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Clinical Pearl: Extra-temporal injuries result in motor weakness only. There is no sensory innervation after the stylomastoid foramen.


Terminal Branches of the Facial Nerve


Key Point

Facial nerve branches can be remembered by the mnemonic: To Zanzibar By Motor Car: Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical

Branches of Facial Nerve

Facial nerve branches can be remembered by the mnemonic: To Zanzibar By Motor Car: Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical.

  • Temporal: innervates the frontalis muscle.
  • Zygomatic: innervates the orbicularis oculi and upper lip elevators
  • Buccal: innervates buccinator and upper lip muscles
  • Marginal: innervates lower lip mouths
  • Cervical branch: platysma

Course of Facial Nerve Branches

The terminal branches of the facial nerve exit the parotid gland deep to the subcutaneous musculoaponeurotic system (SMAS) layer.

Some branches of the facial nerve have vital landmarks:

  • Temporal nerve: Pitanguy's Line (0.5cm below tragus to 1.5cm above lateral brow) in temporoparietal fascia near superficial temporal artery
  • Buccal branch: travels with the parotid duct (Stenson's duct)
  • Marginal mandibular: inferior border of the mandible, deep to the platysma and superficial to the facial artery and anterior facial vein.

Variations in Facial Nerve

Six distinctive anastomotic patterns were initially classified by Davis et al. in 19564, but there is significant variation in the facial nerve due to:

  • No consistent spatial or topographic orientation  
  • Variations in branching patterns and anastomoses between branches5,6
  • The temporal branch and marginal mandibular nerve have less arborization than other facial nerve branches.

These branching pattern variations and cross-innervation clinically correlate to unexplained facial muscle strength in the presence of a known injury to the facial nerve.


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