Facial Nerve Anatomy and Functions

Facial Nerve (VII)

• The facial nerve (VII) emerges from the brain between the pons and medulla.
• It has two roots:
  • A larger motor root originating from the motor nucleus.
  • A smaller root, the nervus intermedius, which carries sensory information.
• The nerve passes into the internal auditory meatus.

Motor Root Functions

• The facial nerve's motor root controls muscles of facial expression.
• It innervates various muscles, including the temporalis, orbicularis oculi, zygomaticus, masseter, buccinator, risorius, and platysma.
• It also controls the stylohyoid muscle and posterior belly of the digastric muscle.

Nervus Intermedius Functions

• This sensory root has special sensory functions related to taste and the external ear.
• It transmits taste sensation from the anterior two-thirds of the tongue.
• It also carries parasympathetic fibers to the submandibular and sublingual salivary glands, as well as lacrimal, nasal, palatine, and pharyngeal glands.

Anatomical Course

• The facial nerve has two main parts: intracranial and extracranial.

• Intracranial: The nerve travels through the cranial cavity.

• Extracranial: The nerve leaves the cranium.

• Three branches emerge before leaving the facial canal:

  • Greater petrosal nerve
    • Parasympathetic fibers to mucous glands of the nose, paranasal sinuses, palate, and lacrimal gland for tear production.
  • Nerve to stapedius
    • Motor fibers to the stapedius muscle of the middle ear for dampening loud noises.
  • Chorda tympani
    • Special sensory fibers to the anterior 2/3 of the tongue for taste. Also parasympathetic fibers to submandibular and sublingual glands.

• The facial nerve then exits the facial canal via the stylomastoid foramen.

• Extracranial branches:

  • Posterior auricular nerve

    • Ascends in front of the mastoid process.
    • Innervates the intrinsic and extrinsic muscles of the outer ear.
    • Supplies the occipital part of the occipitofrontalis muscle.

  • Branches through the parotid gland, terminates into:

    • Temporal Branch
    • Zygomatic Branch
    • Buccal Branch
    • Marginal mandibular Branch
    • Cervical Branch

Damage to the Facial Nerve

• Intracranial lesions occur during the intracranial course, often due to infections of the external or middle ear, or stroke.

• Extracranial lesions can be caused by parotid gland pathology (like tumors or surgery), infections (sometimes viral), or local anesthetic use.

• Symptoms of facial nerve damage may include paralysis or weakness of facial muscles, dry eye, dry mouth, loss of taste, difficulty talking, and reduced salivation.

Examination

• Trigeminal and facial nerve examination is important for diagnosis.