Facial Nerve Anatomy for Surgeons

• The facial nerve, (CN VII), is the seventh paired cranial nerve. 
  • The facial nerve is associated with the derivatives of the second pharyngeal arch.
  • Motor: 
    • Innervates the muscles of facial expression, the posterior belly of the digastric, the stylohyoid and the stapedius muscles.
  • Sensory:
    • A small area around the concha of the auricle.
  • Special Sensory:
    • Provides special taste sensation to the anterior 2/3 of the tongue.
  • Parasympathetic:
    • Supplies many of the glands of the head and neck, including:
      • Submandibular and sublingual salivary glands.
      • Nasal, palatine and pharyngeal mucous glands.
      • Lacrimal glands.

• Anatomical Course:
  • The course of the facial nerve is very complex:
    • There are many branches, which transmit a combination of sensory, motor and parasympathetic fibres.
  • Anatomically, the course of the facial nerve can be divided into two parts:
    • Intracranial:
      • The course of the facial nerve through the cranial cavity, and the cranium itself.
    • Extracranial:
      • The course of the facial nerve outside the cranium, through the face and neck.

• Intracranial portion:
  • The nerve arises in the pons, an area of the brainstem. 
  • It begins as two roots:
    • A large motor root 
    • Small sensory root:
      • The part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve).
  • The two roots travel through the internal acoustic meatus:
    • A 1 cm long opening in the petrous part of the temporal bone. 
      • Here, they are in very close proximity to the inner ear.
  • Still within the temporal bone:
    • The roots leave the internal acoustic meatus, and enter into the facial canal:
      • The facial canal is a ‘Z’ shaped structure.
      • Within the facial canal, three important events occur:
        • Firstly the two roots fuse to form the facial nerve.-
        • Next, the nerve forms the geniculate ganglion:
          • A ganglion is a collection of nerve cell bodies
        • Lastly, the nerve gives rise to:
          • Greater petrosal nerve:
            • Parasympathetic fibers:
              • To mucous glands of the head and neck and lacrimal gland.
          • Nerve to stapedius muscle:
            • Motor fibres to stapedius muscle of the middle ear.
          • Chorda tympani:
            • Special sensory fibers to the anterior 2/3 tongue
            • Parasympathetic fibers to the submandibular and sublingual glands.
  • The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen (in a lateral position):
    • This is an exit located just posterior to the styloid process of the temporal bone.
• Extracranial portion of the facial nerve:
  • 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:
        • 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:
        • Temporal branch
        • Zygomatic branch
        • Buccal branch
        • Marginal mandibular branch
        • Cervical branch
      • These branches are responsible for innervating the muscles of facial expression.
• Motor Functions:
  • Branches of the facial nerve are responsible for innervating many of the muscles of the head and neck.
  • All these muscles are derivatives of the second pharyngeal arch.
  • The first motor branch arises within the facial canal:
    • The nerve to stapedius muscle:
      • The nerve passes through the pyramidal eminence to supply the stapedius muscle in the middle ear.
    • Between the stylomastoid foramen, and the parotid gland, three more motor branches are given off:
      • Posterior auricular nerve:
        • Ascends in front of the mastoid process
        • 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 (a suprahyoid muscle of the neck):
          • It is responsible for raising the hyoid bone.
      • Nerve to the stylohyoid muscle:
        • Innervates the stylohyoid muscle (a suprahyoid muscle of the neck):
          • It is responsible for raising the hyoid bone.
    • Within the parotid gland, the facial nerve terminates by bifurcating into five motor branches:
      • These innervate the muscles of facial expression:
        • Temporal branch:
          • Innervates the frontalis, orbicularis oculi and corrugator supercili
        • Zygomatic branch:
          • Innervates the orbicularis oculi.
        • Buccal branch:
          • Innervates the orbicularis oris, buccinator and zygomaticus muscles.
        • Marginal Mandibular branch:;
          • Innervates the mentalis muscle.
          • Innervates the depressor anguli oris and the depressor labii inferioris
        • Cervical branch:;
          • Innervates the platysma.

• Special 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
    • Travels across the bones of the middle ear
    • Exiting via the petrotympanic fissure, and entering the infratemporal fossa:

      • Here, the chorda tympani ‘hitchhikes’ with 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.

• Parasympathetic functions:

  • The parasympathetic fibres of the facial nerve are carried by the greater petrosal and chorda tympani branches:

    • Greater Petrosal Nerve:

      • The greater petrosal nerve arises immediately distal to the geniculate ganglion within the facial canal:

        • It then moves in anteromedial direction:

          • Exiting the temporal bone into the middle cranial fossa.

            • From here, its travels across (but not through) the foramen lacerum:

              • Combining with the deep petrosal nerve to form the nerve of the pterygoid canal:

                • The nerve of pterygoid canal then passes through the pterygoid canal (Vidian canal) to enter the pterygopalatine fossa, and synapses with the pterygopalatine ganglion.

                  • Branches from this ganglion then go on to provide parasympathetic innervation to the mucous glands of the oral cavity, nose and pharynx, and the lacrimal gland.

• Chorda Tympani:
  • The chorda tympani also carries some parasympathetic fibres:
    • These combine with the lingual nerve (a branch of the trigeminal nerve) in the infratemporal fossa and form the submandibular ganglion:
      • Branches from this ganglion travel to the submandibular and sublingual salivary glands.

Rodrigo Arrangoiz MS, MD, FACS a head and neck surgeon / surgical oncologist and is a member of Sociedad Quirúrgica S.C at the America British Cowdray Medical Center in Mexico City:

• He is an expert in the management of head and neck cancers.

 

Training:

• General surgery:

• Michigan State University:

• 2004 al 2010

• Surgical Oncology / Head and Neck Surgery / Endocrine Surgery:

• Fox Chase Cancer Center (Filadelfia):

• 2010 al 2012

• Masters in Science (Clinical research for health professionals):

• Drexel University (Filadelfia):

• 2010 al 2012

• Surgical Oncology / Head and Neck Surgery / Endocrine Surgery:

• IFHNOS / Memorial Sloan Kettering Cancer Center:

• 2014 al 2016

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