Facial nerve: movement, taste, and expression

The facial nerve is the seventh cranial nerve, usually written as CN VII. It is a mixed nerve: different fibres carry movement signals, taste information, and parasympathetic signals that help regulate certain glands.

Although it is often introduced as the nerve of facial expression, its work is broader. It helps close the eyes, move the lips and cheeks, carry taste from the front part of the tongue, and support tear and saliva production.

Origin and course of the facial nerve

The facial nerve begins in the brainstem near the junction between the pons and medulla. Its motor root curves around the abducens nerve nucleus before leaving the brainstem; this course contributes to a raised area called the facial colliculus in the floor of the fourth ventricle.

The nerve then travels with the vestibulocochlear nerve through the internal acoustic meatus and enters the facial canal in the temporal bone. A swelling called the geniculate ganglion lies along this route. The nerve leaves the skull through the stylomastoid foramen and divides into branches that reach muscles and glands of the face.

Functional components and related nuclei

Three broad functional groups are useful for understanding CN VII:

• Motor fibres: supply muscles of facial expression and several small muscles in the head and neck.
• Taste fibres: carry taste information mainly from the anterior two-thirds of the tongue through the chorda tympani.
• Parasympathetic fibres: help control secretion from the lacrimal, submandibular, and sublingual glands.

These functions are associated with several brainstem nuclei. The main motor nucleus controls facial movement. Taste information connects with the nucleus of the solitary tract, while parasympathetic pathways are linked with the superior salivatory and lacrimal nuclei.

Main branches

Chorda tympani

The chorda tympani carries taste information from the front portion of the tongue and also carries parasympathetic fibres involved in salivary secretion. It joins the lingual nerve before reaching its targets.

Greater petrosal nerve

The greater petrosal nerve carries parasympathetic fibres towards pathways that support lacrimal secretion. It joins the deep petrosal nerve to continue through the pterygoid canal.

Terminal branches

After leaving the skull and passing through the parotid region, the facial nerve divides into five commonly named terminal branches:

• Temporal: supplies muscles around the forehead and upper eye.
• Zygomatic: supports muscles around the eye.
• Buccal: supplies muscles of the cheek, including the buccinator.
• Marginal mandibular: supplies muscles that move the lower lip.
• Cervical: supplies the platysma in the neck.

Functions of the facial nerve

Facial movement

CN VII supplies the muscles that create expressions such as smiling, frowning, closing the eyes, and wrinkling the forehead. It also supplies the stapedius, stylohyoid, posterior belly of the digastric, and platysma muscles.

Taste

The chorda tympani carries taste signals from much of the anterior two-thirds of the tongue. General sensations such as touch and pain from the face are mainly carried by the trigeminal nerve instead.

Tears and saliva

Parasympathetic fibres of the facial nerve help stimulate the lacrimal gland and the submandibular and sublingual salivary glands. The nerve therefore contributes to keeping the eye and mouth moist.

The tear reflex

When the cornea is irritated, sensory information travels through the ophthalmic division of the trigeminal nerve. Connections in the brainstem then activate facial-nerve parasympathetic pathways, increasing tear production.

Facial nerve conditions and assessment

Facial weakness

Damage to the facial nerve can cause weakness on one side of the face. Depending on where the pathway is affected, a person may have difficulty closing an eye, moving the mouth, tasting food, or producing tears and saliva. Bell’s palsy is one recognised cause of acute facial weakness, but facial weakness has several possible causes.

New or sudden facial weakness requires prompt medical assessment, particularly when it occurs with other neurological symptoms. This guide is educational and cannot identify the cause of an individual symptom.

How clinicians assess the nerve

A clinical examination may include asking a person to raise the eyebrows, close the eyes firmly, smile, show the teeth, puff out the cheeks, or move the lips. Taste, hearing, tear production, and other findings may also help locate the affected part of the pathway.

Summary

The facial nerve is cranial nerve VII and has motor, taste, and parasympathetic functions. It begins in the brainstem, travels through the temporal bone, leaves the skull near the base of the ear, and divides into branches that serve the face and neck.

Its best-known role is facial expression, but it also contributes to taste from the front of the tongue, tear production, salivary secretion, and the protection of the eye through facial movement and reflex pathways.

Next related guide: Hypoglossal nerve