Anatomy and Structure of the Facial Nerve
- The facial nerve emerges from the pons of the brainstem.
- It travels through the facial canal in the temporal bone.
- The nerve exits the skull at the stylomastoid foramen.
- The facial and intermediate nerves are collectively referred to as the nervus intermediofacialis.
- The greater petrosal nerve provides parasympathetic innervation to several glands.
- The communicating branch to the otic ganglion joins the lesser petrosal nerve.
- The nerve to stapedius provides motor innervation for the stapedius muscle.
- The chorda tympani provides parasympathetic innervation to sublingual and submandibular glands.
- The chorda tympani also supplies taste fibers for the anterior two-thirds of the tongue.
- The cell bodies for the facial nerve are grouped in nuclei or ganglia.
- Afferent nerve cell bodies are found in the geniculate ganglion.
- Muscular efferent nerve cell bodies are found in the facial motor nucleus.
- Parasympathetic efferent nerve cell bodies are found in the superior salivatory nucleus.
- The facial nerve is derived from the second pharyngeal arch.
- It supplies motor and sensory innervation to muscles formed by the second pharyngeal arch.
- The motor division of the facial nerve originates from the embryonic pons.
- The sensory division of the facial nerve originates from the cranial neural crest.
- Taste fibers for the anterior two-thirds of the tongue are supplied by the chorda tympani branch.

Functions of the Facial Nerve
- The main function of the facial nerve is motor control of facial expression muscles.
- It also innervates muscles such as the posterior belly of the digastric and stylohyoid.
- The facial nerve receives taste sensations from the anterior two-thirds of the tongue.
- Taste sensation is sent to the gustatory portion of the solitary nucleus.
- General sensation from the anterior two-thirds of the tongue is supplied by the fifth cranial nerve.
- Supplies parasympathetic fibers to the submandibular and sublingual glands, increasing saliva flow.
- Provides parasympathetic innervation to the nasal mucosa and lacrimal gland.
- Functions as the efferent limb of the corneal reflex.
- Carries axons for general somatic afferent (GSA) to the skin of the posterior ear.
- Carries axons for general visceral efferent (GVE) to the sublingual, submandibular, and lacrimal glands.

Clinical Significance - Facial Nerve Palsy
- Acute facial nerve paralysis can result in facial paralysis.
- Bells palsy is a type of idiopathic acute facial nerve paralysis, often caused by viral infection or Lyme disease.
- Iatrogenic Bells palsy can occur due to incorrectly placed dental anesthesia.
- Surgery, such as cross facial nerve graft or masseteric facial nerve transfer, may be performed to restore facial movement.
- Facial nerve decompression surgery is sometimes done in cases of facial nerve compression.

Examination of the Facial Nerve
- Voluntary facial movements test the facial nerve, including wrinkling the brow, showing teeth, frowning, closing the eyes tightly, pursing the lips, and puffing out the cheeks.
- Upper motor neuron lesion (central seven) affects the lower part of the face on the contralateral side.
- Lower motor neuron lesions can result in CN VII palsy, causing weakness in both upper and lower facial muscles on the same side.
- Taste can be tested on the anterior two-thirds of the tongue using a flavored solution or electronic stimulation.
- The corneal reflex tests the proper functioning of both cranial nerves V and VII, involving consensual blinking of both eyes in response to stimulation of one eye.

Additional Information
- Inferior view of the human brain shows labeled cranial nerves, including the facial nerve.
- Mandibular division of the trigeminal nerve is shown.
- The course and connections of the facial nerve in the temporal bone are depicted.
- Images show the surface markings for the tympanic antrum, transverse sinus, and facial nerve in the left temporal bone.
- Illustrations display the branches of the facial nerve and deep dissection of the nerve.