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Facial Nerve Anatomy (CN VII)

The facial nerve Anatomy is the seventh cranial nerve that is made up of a sensory (intermediate) root, which conveys taste, and a motor root, the facial nerve proper, which supplies the muscles of facial expression, the platysma muscle, and the stapedius muscle of the inner ear.

Facial Nerve Course

The Facial Nerve Course can be divided into Intracranial (the course of the facial nerve in the cranial cavity, and the cranium itself) and Extracranial (the course of the nerve outside the cranium, through the face and neck).

See Also: Cranial Nerves

Intracranial Facial Nerve Anatomy

The Facial Nerve arises in the pons, an area of the brainstem. It begins as two roots; a large motor root, and a small sensory root (intermediate nerve). The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear.

The roots leave the internal acoustic meatus, and enter into the facial canal which takes a ‘Z’ shaped liked structure. Within the facial canal, three important events occur:

  1. Firstly the two roots fuse to form the facial nerve.
  2. Next, the nerve forms the geniculate ganglion.
  3. Lastly, the nerve gives rise to:
    • Greater petrosal nerve, parasympathetic fibres to mucous glands and lacrimal gland.
    • Nerve to stapedius – motor fibres to stapedius muscle of the middle ear.
    • Chorda tympani – special sensory fibres to the anterior 2/3 tongue and parasympathetic fibres to the submandibular and sublingual glands.

The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen just posterior to the styloid process of the temporal bone.

Facial Nerve Course
Facial nerve diagram

Extracranial Facial Nerve Anatomy

After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear.

The first extracranial branch to arise is the posterior auricular nerve. It provides motor innervation to the some of the muscles around the ear. Immediately distal to this, motor branches are sent to the posterior belly of the digastric muscle and to the stylohyoid muscle.

The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid gland (note – the facial nerve does not contribute towards the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve).

Within the parotid gland, the nerve terminates by splitting into five branches:

  1. Temporal branch
  2. Zygomatic branch
  3. Buccal branch
  4. Marginal mandibular branch
  5. Cervical branch

These branches are responsible for innervating the muscles of facial expression.

CN VII

Motor Functions

Nerve to stapedius muscle is the first motor branch arises within the facial canal.

Between the stylomastoid foramen, and the parotid gland, three motor branches are given:

  • Posterior auricular nerve: innervates the intrinsic and extrinsic muscles of the outer ear. It also supplies the occipital part of the occipitofrontalis muscle.
  • Nerve to the posterior belly of the digastric muscle: Innervates the posterior belly of the digastric muscle. It is responsible for raising the hyoid bone.
  • Nerve to the stylohyoid muscle: Innervates the stylohyoid muscle. It is responsible for raising the hyoid bone.

The facial nerve terminates by bifurcating into five motor branches. These innervate the muscles of facial expression:

  1. Temporal:  Innervates the frontalis, orbicularis oculi and corrugator supercilii.
  2. Zygomatic: Innervates the orbicularis oculi.
  3. Buccal: Innervates the orbicularis oris, buccinator and zygomaticus.
  4. Marginal mandibular: Innervates the depressor labii inferioris, depressor anguli oris and mentalis.
  5. Cervical: Innervates the platysma.
Facial Nerve Anatomy (CN VII)

Sensory Functions

The chorda tympani branch of the facial nerve is responsible for innervating the anterior 2/3 of the tongue with the special sense of taste.

The nerve arises in the facial canal, and travels across the bones of the middle ear, exiting via the petrotympanic fissure, and entering the infratemporal fossa.

Within the infratemporal fossa, the chorda tympani ‘hitchhikes’ upon the lingual nerve. The parasympathetic fibres of the chorda tympani stay with the lingual nerve, but the main body of the nerve leaves to innervate the anterior 2/3 of the tongue.

NerveFunctional ComponentsCells of Origin/TerminationCranial ExitDistribution and Functions
Temporal, zygomatic, buccal, mandibular, cervical, and posterior auricular nerves, nerve to posterior belly of digastric, nerve to stylohyoid, nerve to stapediusSomatic (branchial) motorMotor nucleus of CN VIIStylomastoid foramenMotor to muscles of facial expression and scalp; also supplies stapedius of middle ear, stylohyoid, and posterior belly of digastric
Intermediate nerve through chorda tympaniSpecial sensoryGeniculate ganglion/solitary nucleusInternal acoustic meatus/facial canal/petrotympanic fissureTaste from anterior two thirds of tongue, through chorda tympani floor of mouth, and palate
Intermediate nerveSomatic (general) sensoryGeniculate ganglion/spinal
trigeminal nucleus
Internal acoustic meatusSensation from skin of external acoustic meatus
Intermediate nerve through greater petrosal nerveVisceral sensoryNuclei of solitary tractInternal acoustic meatus/facial canal/ foramen for greater petrosal nerveVisceral sensation from mucous membranes of nasopharynx and palate
Greater petrosal nerve Chorda tympaniVisceral motorPresynaptic: superior salivatory nucleus; Postsynaptic: pterygopalatine ganglion (greater petrosal nerve) and submandibular ganglion (chorda tympani)Internal acoustic meatus/facial canal/ foramen for greater petrosal nerve, (greater petrosal nerve) petrotympanic fissure (chorda tympani)Parasympathetic innervation to lacrimal gland and glands of the nose and palate (greater petrosal nerve); submandibular and sublingual salivary glands (chorda tympani)

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