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Facial nerve

In this article we will discuss the facial nerve, its anatomy and functions as well as some related clinical conditions. 

As you go through your day, think about how you interact with other people. You speak to them, yes; but while that is a very direct form of communication, you also use a number of other less obvious–even less conscious–methods to communicate your opinions and emotions on a regular basis.

One of the most important ways we non-verbally communicate with each other is by facial expression. A lift of an eyebrow, the wrinkling of a nose, or the slight twinge of the corner of the mouth can tell us quite a bit: if we are paying attention, we notice these small changes and interpret not only what they indicate about the people we are interacting with, but also what they indicate regarding their demeanor towards us, and the relationships forming between us.

Like Mona Lisa’s mysterious, captivating, and somewhat evasive smile, one small visually-observable change in facial expression can speak volumes without having to say a single word.

Key facts
Type Mixed nerve (motor, sensory, autonomic fibers)
Origin Pons of the brainstem
Intracranial branches Greater petrosal nerve, communicating branch with otic ganglion, nerve to stapedius, chorda tympani
Extracranial branches Posterior auricular nerve, branch to posterior digastric belly, branch to stylohyoid muscle, temporal branch, zygomatic branch, buccal branch, marginal mandibular branch, cervical branch
Field of innervation Motor: facial expression muscles, posterior belly of digastric muscle, stylohyoid muscle, stapedius muscle
Special sensory: taste from anterior two-thirds of the tongue
Parasympathetic: submandibular gland, sublingual gland, lacrimal glands
Clinical relations Palsy, inferior medial pontine syndome

Regarding facial expression, there is one vitally important nerve that allows us to partake in this form of communication, and it is aptly named the facial nerve. While it is indeed responsible for innervating the muscles of facial expression, the facial nerve is a complex structure containing many fiber types with a variety of functions, including motor, sensory, and autonomic. The following article will discuss the importance and versatility facial nerve.

  1. The cranial nerves
  2. The facial nerve
    1. Components and branches
    2. Origin and course
  3. The muscles of facial expression
    1. Orbital group
    2. Nasal group
    3. Oral group
    4. Other muscles
  4. The facial nerve as part of the corticobulbar tract
  5. Clinical notes
    1. Surgical removal of the parotid gland
    2. Facial nerve palsy
    3. Inferior medial pontine syndrome
    4. Clinical case
  6. Sources
+ Show all

The cranial nerves

The facial nerve is one of a group of nerves called the cranial nerves (CN), twelve pairs of nerves that, with the exception of the spinal accessory nerve (CN XI), originate in the brain and contribute to the peripheral nervous system (PNS). They are referred to as “cranial” because they arise from the brain and upper spinal cord and supply structures of the head and neck.

The 12 paired cranial nerves include:

Some of these contain motor fibers, some contain autonomic fibers, some contain somatic sensory fibers, some contain special sensory fibers, and some contain combinations of a number of these aforementioned fiber types. CN I, CN II, CN VII, CN VIII, CN IX and CN X play roles in special sensory functions (i.e. olfaction, vision, gustation, audition, and balance); CN V (all three branches, the ophthalmic, maxillary, and mandibular) and CN IX play roles in somatic sensory functions; CN III, CN IV, CN V (the mandibular branch, V3, only), CN VI, CN VII, CN IX, CN X, CN XI, and CN XII are responsible for motor functions; and CN III, CN VII, CN IX, and CN X have important autonomic functions.

The cranial nerves can be a total pain to understand. Want a faster way to learn? Our cranial nerves quizzes and labeled diagrams have your back!

The facial nerve

Components and branches

The facial nerve contains many different types of fibers, including general sensory (afferent) fibers, special sensory fibers, visceral/autonomic motor (efferent) fibers, and somatic motor fibers.

General sensory fibers in the facial nerve are responsible for transmitting signals to the brain from the external acoustic meatus, as well as the skin over the mastoid and lateral pinna. Special sensory fibers in the facial nerve are responsible for receiving and transmitting taste information from the anterior two-thirds of the tongue.

Visceral/autonomic motor fibers in the facial nerve are responsible for innervating the lacrimal gland, submandibular gland, sublingual gland, and the mucous membranes of the nasal cavity and hard and soft palates, allowing for production of tears, saliva, etc., from these locations. Somatic motor fibers in the facial nerve are responsible for innervating the muscles of facial expression and muscles in the scalp (which are derived from the second pharyngeal arch), as well as the stapedius muscle in the ear, the posterior belly of the digastric muscle, and the stylohyoid muscle.

To remember the branches of the facial nerve, you can use the following mnemonic: "To Zanzibar By Motor Car", standing for Temporal, Zygomatic, Buccal, Marginal mandibular and Cervical branches.

Origin and course

The motor root of the facial nerve originates in the facial (motor) nerve nucleus in the pons of the brainstem, which receives input from a number of other structures and brain regions, including the primary motor cortex and the ophthalmic division of the trigeminal nerve.

The fibers travel towards the floor of IV ventricle and go around the abducens nucleus and descend. The facial nerve emerges from the lateral surface of brainstem at the pontine-medullary junction between the VI and VIII nerves.

The motor root travels with the nervus intermedius (a smaller sensory root containing parasympathetic fibers, general sensory fibers, and special sensory fibers) in the cerebellopontine angle and enters the internal auditory meatus of the temporal bone accompanied by the vestibulocochlear nerve (CN VIII) and the labyrinthine artery and vein.

The facial nerve roots then enter the facial canal in petrous part of temporal bone, where the small sensory and large motor roots fuse, forming the facial nerve. This united nerve enlarges at the geniculate ganglion, which contains cell bodies for sensory neurons.

It is here, at the geniculate ganglion in the facial canal of the temporal bone, that the facial nerve gives off the greater petrosal nerve, the first in a series of nerves which eventually carry preganglionic parasympathetic fibers to the lacrimal gland, stimulating lacrimation (tearing). It passes beneath the trigeminal ganglion and reach the foramen lacerum where it is joined by deep petrosal nerve to become the nerve of the pterygoid canal (Vidian nerve). The greater petrosal nerves contain parasympathetic fibers for the pterygopalatine ganglion and taste fibers. As the facial nerve continues to travel along bony canal, two more branches emerge: the nerve to stapedius, the chorda tympani, and preganglionic parasympathetic fibers.

The nerve to stapedius innervates the stapedius muscle, as its name suggests. The stapedius muscle attaches to the posterior surface of the stapes, one of the three ossicles of the middle ear. The stapedius muscle contracts in response to loud noises, preventing excessive oscillation of the stapes, thereby dampening its vibrations and controlling the amplitude of sound waves.

The chorda tympani leaves the facial nerve above the stylomastoid foramen and is responsible for transmitting taste sensation, via the aforementioned special sensory fibers, from the anterior two-thirds of the tongue. It passes through the posterior wall of the middle ear, crosses the neck of the malleus and emerges at the medial end of petrotympanic fissure. It joins the posterior aspect of lingual nerve at an acute angle and carries taste fibers for the anterior two-third of tongue and efferent preganglionic parasympathetic fibers to the submandibular ganglion which are responsible for innervating the submandibular gland, stimulating salivary secretions.

The facial nerve exits skull via stylomastoid foramen; nearby, it gives off the posterior auricular nerve which is meant to supply the occipital belly of the occipitofrontalis muscle and some of the auricular muscles, and nerves to the posterior belly of the digastric and the stylohyoid. The nerve then enters the parotid gland, from whence it gives off five terminal branches–the temporal, zygomatic, buccal, marginal mandibular, and cervical branches–which emerge from around the parotid gland and innervate structures across the entire face.

Notice how the facial nerve penetrates the parotid gland. But note that it doesn't innervate it; instead, the gland is innervated by the glossopharyngeal nerve.

The muscles of facial expression

Now we will return to the topic of conversation first introduced in our discussion of the facial nerve: the facial muscles that it innervates, which allow for us to nonverbally communicate with others via our facial expressions.

The muscles of facial expression, innervated by the branches of the facial nerve, are divided into groups by their locations: these include the orbital group, the nasal group, and the oral group, as well as a group of auricular muscles and the occipitofrontalis.   

Orbital group

The orbital group of facial muscles consists of the corrugator supercilii muscle and the orbicularis oculi muscle. The corrugator supercilii muscle pulls the eyebrows medially and downward. The orbicularis oculi muscle has two parts: a palpebral part and an orbital part. The palpebral part is responsible for gently closing the eyelids, while the orbital part is responsible for forcefully closing the eyelids.

The orbicularis oculii are the effector muscles of the efferent limb of the corneal reflex, or blink reflex: when sensory nerve endings of the ophthalmic branch of the trigeminal nerve in the cornea are stimulated, these nerve endings transmit a signal to the trigeminal sensory nucleus, which communicates this signal to both facial motor nuclei. The facial motor nuclei then send signals to the orbicularis oculi muscles of both eyes to contract via the temporal and zygomatic branches of the facial nerve. This causes the eyelids to close, effectively protecting the eyes from foreign bodies.

Nasal group

The nasal group of facial muscles consists of the nasalis muscle, the procerus muscle, and the depressor septi muscle. The nasalis muscle has two parts: the transverse part, which compresses the nasal aperture, and the the alar part, which pulls the alar cartilage laterally and downward, allowing the nostrils to open.

The procerus muscle pulls the medial angle of the eyebrows downward, producing wrinkling across the bridge of the nose. As it suggests, in the region of the nasal septum, the depressor septi pulls the tip of the nose downward.

Oral group

The oral group of facial muscles consists of:

The depressor anguli oris  muscle pulls the corners of the mouth downward and laterally into a frown. The depressor labii inferioris muscle, as its name suggests, pulls the lower lip downward and laterally. The mentalis muscle wrinkles the skin on the chin, and raises and protrudes the lower lip. The risorius muscle and zygomaticus major and minor muscles work together to facilitate smiling: the risorius retracts the corners of the mouth upward, the zygomaticus major pulls the corners of the mouth upward and laterally, and the zygomaticus minor raises the upper lip.

The levator labii superioris, as suggested by its name, raises the upper lip; and, along with the levator anguli oris which raises the corners of the mouth, forms the nasolabial furrow. The levator labii superioris alaeque nasi acts to raise the upper lip and open the nostril. The orbicularis oris acts to close and protrude the lips; and, finally, the buccinator compresses the cheeks against the teeth.

Other muscles

Other muscles innervated by branches of the facial nerve are the anterior, superior, and posterior auricular muscles; and the occipitofrontalis muscle. The anterior, superior, and posterior auricular muscles all elevate the ear by pulling it upward.

As their names suggest, the anterior auricular muscle pulls the ear anteriorly in addition to superiorly, and the posterior auricular muscle pulls the ear posteriorly in addition to superiorly. The occipitofrontalis muscle has two parts: the frontal belly, which raises the eyebrows resulting in wrinkling of the forehead, and the occipital belly, which pulls the scalp backward.

The facial nerve as part of the corticobulbar tract

The corticobulbar tract, or corticonuclear tract, influences the motor nuclei of many of the cranial nerves with motor components. In addition to the facial nerve, these include:

  • the oculomotor (III)
  • trochlear (IV)
  • mandibular component of the trigeminal (V3)
  • abducens (VI)
  • glossopharyngeal (IX)
  • vagus (X)
  • spinal accessory (XI)
  • hypoglossal (XII) nerves
Corticobulbar tract - axial view

For the innervation of facial muscles, the corticobulbar tract sends motor signals via a sequence of two motor neurons: signals originating in the cell bodies of the upper motor neurons (UMNs) of the lateral cerebral cortex corresponding to the different parts of the face descend from the cortex, through the internal capsule, and synapse on the cell bodies of lower motor neurons (LMNs) which are located in the facial nerve nuclei of the pons in the upper brainstem. These signals are then transmitted from LMN cell bodies into their axons, which project via the facial nerve motor root to the muscles of facial expression. Axons originating from UMNs are considered part of the corticobulbar tract, whereas axons originating from LMNs are considered part of the cranial nerves themselves.

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