Table of ContentsView AllTable of ContentsAnatomyFunctionAssociated ConditionsRehabilitation
Table of ContentsView All
View All
Table of Contents
Anatomy
Function
Associated Conditions
Rehabilitation
The facial nerve and its branches regulate a number of functions of the mouth and face. Most of its divisions stimulate muscles that allow eyelids to open and close, as well as facial movements. This nerve also mediates the production of tears and saliva and the perception of taste in the tongue and receives some sensory input from the face as well. The facial nerve is the seventh of the12 cranial nerves.
Bell’s palsyis the most common medical problem involving theseventh cranial nerve. It is an impairment of the function of the facial nerve that causes weakness of one side of the face.
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The facial nerve has a complex anatomy. It is one of the longest cranial nerves, extending from thebrainstemto the terminal (end) branches, which are located throughout the face. Several structures of the facial nerve—described as nuclei, segments, and branches—produce the four components of facial nerve function.
The facial nerve has:
Structure
The brainstem nuclei of the facial nerve are part of thecentral nervous system (CNS), while the facial nerve itself is aperipheral nerve. The facial nerve nuclei in the brainstem are called the:
As the facial nerve emerges from the brainstem, it divides into smaller branches that travel towards the muscles and glands in the face.
Six of the facial nerve branches control facial movement:
Location
The facial nerve emerges at the pontine level of the brainstem. The brainstem is the part of the brain that is continuous with thespinal cord. It includes three sections:
The tympanic segment runs through the bones of the middle ear. The mastoid segment, which follows, has three branches, and the extratemporal segment branches into the nerves that control the face.
Anatomic Variations
Minor differences in the structure and location of the branches of the facial nerve are not usually noticeable. These differences may be picked up when detailed imaging studies are performed for a medical reason.
Variations can be challenging when it comes to surgical procedures that involve the facial nerve. Pre-operative planning involves imaging, typically with contrast dye, to identify the anatomy of the nerve and detect variations ahead of time.
The four components of the facial nerve include motor, sensory, taste, and parasympathetic function.
Motor
Most of the branches of the facial nerve are motor branches that stimulate the movement of the facial muscles. These muscles include the:
Sensory
The facial nerve detects sensation from the small area behind the ear described as the auricle. The sensory information from this area is transmitted through the facial nerve to the brainstem, then to the thalamus in the brain, and eventually to the cerebral cortex, where the brain can integrate and make sense of the sensation.
Taste
Parasympathetic
Nerve branches of the facial nerve simulate glands in the face. Thelacrimal glandsare located around the eyes. These glands regularly produce small amounts oftearsto lubricate and protect the eyes. They also produce more tears when a person cries.
Thesubmandibular glandsnear the mouth produce saliva to lubricate the inside of the mouth and to help with breaking down food. And thesublingual glandsin the lower part of the mouth produce saliva as well. Parasympathetic branches of the facial nerve also stimulate mucous glands of the nose.
The parasympathetic function of the facial nerve is closely linked with thehypothalamus, which is an area of the brain that detects emotions and mediates certain survival functions, such as digestion.
Control of the Facial Nerve From the Brain
The function of the facial nerve is interesting because some motor branches of the facial nerve have bilateral (both sides) control from the brain and some only have unilateral (from one side) control from the brain. Nerve stimulation of muscle movement originates from the motor area of the cerebral cortex and crosses to the other side of the brain in the brainstem before transmitting impulses to the facial nerve.
The fascinating thing about this redundancy is that if the facial nerve can’t function properly due to a problem in the brain, the muscles of the forehead can still move.
When the area of the brain that controls the face becomes damaged, only the lower two-thirds of the face becomes weak.
On the other hand, if the facial nerve itself or its nuclei in the brainstem are damaged or impaired, then the entire side of the face becomes weak—resulting in more substantial and visibly obvious impairment of facial movement.
There are a few medical conditions that result in decreased function of the facial nerve. The symptoms typically involve weakness of the face because most branches of the facial nerve control facial movement. However, impairment of any of the other three components of facial nerve function can occur as well.
Bell’s Palsy
The most common condition affecting this cranial nerve, Bell’s palsy, can occur without a known cause (idiopathic) or as the result of a viral infection. The symptoms are usually very noticeable, with complete or partial paralysis of one side of the face, including the forehead.
Bell’s palsy can be very distressing, often causing trouble speaking or even chewing. One eye can become dry, red, and irritated because it can be difficult to shut the eyelid. Tear production can be impaired as well.
It usually improves on its own, but it is best to seek medical attention because facial nerve weakness can occur as a result of other causes, including tumors or serious infections.
Stroke
A stroke is an interruption of blood flow in the brain. A stroke does not directly injure the facial nerve, but it can cause the decreased function of the facial nerve due to a lack of signals from the cerebral cortex, causing weakness in the contralateral lower portion of the face.
The effects are not as noticeable as the effects of Bell’s palsy because the forehead is still able to move due to its bilateral facial nerve control from the brain. However, a stroke is a serious condition requiring urgent medical attention. If you have had a stroke, this is also a sign that you could be at risk of having a heart attack or another stroke, so it is important to follow up with your healthcare provider to address the prevention ofvascular disease.
Ramsay Hunt Syndrome
Shingles, which is a reactivation of herpes zoster (the chickenpox virus) can affect any nerve, including the facial nerve. Shingles affecting the facial nerve is described as Ramsay Hunt syndrome.
The symptoms of Ramsay Hunt syndrome include face weakness and a skin rash on one side of the face. This condition can also cause decreased sensation, dizziness, or hearing loss. Ramsay Hunt syndrome can resolve on its own, but any of its effects may be permanent in severe cases.
Guillain-Barre Syndrome (GBS)
Also described as acute demyelinating polyneuropathy, or acute ascending polyneuropathy, this is a disease of the peripheral nerves that can affect both facial nerves at the same time.GBSusually begins in the feet, causing weakness. It may rapidly worsen, causing ascending (climbing) weakness in the legs, breathing muscles, arms, and face.
This syndrome can begin suddenly and it may be fatal due to the weakness of the breathing muscles. If you develop GBS, you can recover if you are treated with respiratory support—which may require a mechanical ventilator—until the condition resolves.
Aneurysm
An out-pouching of a blood vessel can compress the facial nerve or one of its branches and may cause facial weakness or hemifacial spasm.
Infection
An infection such asLyme diseasecan preferentially attack one or both facial nerves, causing temporary or long-term symptoms. If the infection is identified, antibiotics can help hasten recovery and may prevent permanent damage and dysfunction of the nerve.
Traumatic Injury
Head or face trauma can injure the facial nerve or one of its branches, potentially causing weakness of some muscles of the face, as well as the impaired function of any of the components of the facial nerve.
Tumor
Abrain tumoror metastatic (spreading) cancer from the body can compress or invade the facial nerve nuclei or a segment or branch of the facial nerve, causing impaired function, typically on one side of the face. A large tumor can compress both nuclei in the brainstem, however, producing symptoms on both sides of the face.
If you have had any type of facial nerve disease or injury, recovery includes physical therapy, which can help your face and mouth muscles regain at least some of their strength. The extent of recovery depends on the type and severity of the damage, how much of the nerve was involved, and the type of disease.
If you have a tumor or some other mass putting pressure on the facial nerve, surgical removal of the mass may help alleviate the nerve impairment. Facial nerve reconstruction and grafting are methods that have been used to repair a damaged facial nerve.
These procedures may improve motor function for some facial nerve injuries. Techniques include stereotactic and minimally invasive procedures, as well as more extensive open procedures.
11 Sources
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