Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk. Some of the cranial nerves are involved in the special senses (such as seeing, hearing, and taste), and others control muscles in the face or regulate glands. The nerves are named and numbered (according to their location, from the front of the brain to the back).
Viewing the Cranial Nerves
Twelve pairs of cranial nerves emerge from the underside of the brain, pass through openings in the skull, and lead to parts of the head, neck, and trunk.
A cranial nerve disorder may result when the following are damaged or malfunction:
Areas of the brain that control cranial nerves (called centers, or nuclei), as may occur when a stroke Symptoms A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more damages the area that controls the facial nerve
The nerve fibers that connect cranial nerve centers within the brain, as occurs in internuclear ophthalmoplegia Internuclear Ophthalmoplegia Internuclear ophthalmoplegia is impairment of horizontal eye movements caused by damage to certain connections between nerve centers in the brain stem (the lower part of the brain). In internuclear... read more
Only one cranial nerve, as occurs in oculomotor palsy Third Cranial Nerve (Oculomotor Nerve) Palsy A palsy of the 3rd cranial nerve can impair eye movements, the response of pupils to light, or both. These palsies can occur when pressure is put on the nerve or the nerve does not get enough... read more , trigeminal neuralgia Trigeminal Neuralgia Trigeminal neuralgia is severe facial pain due to malfunction of the 5th cranial nerve (trigeminal nerve). This nerve carries sensory information from the face to the brain and controls the... read more , Bell palsy Bell Palsy Bell palsy (a type of facial nerve palsy) is sudden weakness or paralysis of muscles on one side of the face due to malfunction of the 7th cranial nerve (facial nerve). This nerve moves the... read more , and hemifacial spasm Hemifacial Spasm Hemifacial spasm is painless involuntary twitching of one side of the face due to malfunction of the 7th cranial (facial) nerve and/or the area of the brain that controls it (called a center... read more
Some cranial nerve disorders interfere with eye movement. Eye movement is controlled by 3 pairs of muscles. These muscles move the eye up and down, right and left, and diagonally. The muscles are controlled by the following cranial nerves:
If one of these nerves or the area in the brain that controls these muscles is damaged, the muscles may become paralyzed to varying degrees (called a palsy), and people may not be able to move their eyes normally. How eye movement is affected depends on which nerve is affected. People with one of these palsies may have double vision when they look in certain directions.
Did You Know...
Cranial nerve disorders have many causes, including the following:
Infections, such as COVID-19 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more , Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These... read more , and shingles Shingles Shingles is a painful skin rash caused by a viral infection that results from reactivation of the varicella-zoster virus, the virus that causes chickenpox. What causes the virus to reactive... read more
An inadequate blood supply (as occurs in diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more or stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more )
Pressure on a nerve due to abnormalities in blood vessel, such as a bulge (aneurysm Aneurysms of Arteries in the Arms, Legs, and Heart An aneurysm is a bulge (dilation) in the wall of an artery. (See also Aortic Branch Aneurysms and Brain Aneurysms.) Aneurysms may occur in any artery. Aneurysms are most common in the aorta... read more ) in an artery or an abnormal connection between an artery and a vein (arteriovenous malformation Arteriovenous Fistula An arteriovenous fistula is an abnormal channel between an artery and a vein. Rarely, a large fistula may divert enough blood to cause symptoms of reduced blood flow in the affected arm or leg... read more )
Disorders that cause nerve cells to degenerate, as occurs in amyotrophic lateral sclerosis Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs) Motor neuron diseases are characterized by progressive deterioration of the nerve cells that initiate muscle movement. As a result, the muscles stimulated by these nerves deteriorate, become... read more (ALS) or multiple sclerosis Multiple Sclerosis (MS) In multiple sclerosis, patches of myelin (the substance that covers most nerve fibers) and underlying nerve fibers in the brain, optic nerves, and spinal cord are damaged or destroyed. The cause... read more
Disorders that cause inflammation of blood vessels (vasculitis), such as giant cell arteritis Giant Cell Arteritis Giant cell arteritis is chronic inflammation of large and medium arteries of the head, neck, and upper body. Typically affected are the temporal arteries, which run through the temples and provide... read more
Certain drugs, particularly antibiotics such as aminoglycosides Aminoglycosides Aminoglycosides are a class of antibiotics used to treat serious bacterial infections, such as those caused by gram-negative bacteria (especially Pseudomonas aeruginosa). Aminoglycosides... read more and streptomycin
Some toxins, such as mercury
Symptoms of cranial nerve disorders depend on which nerves are damaged and how they were damaged. Cranial nerve disorders can affect smell, taste, vision, sensation in the face, facial expression, hearing, balance, speech, swallowing, and muscles of the neck.
For example, vision may be affected in various ways:
If any of the three cranial nerves that control eye movement (3rd, 4th, or 6th cranial nerve) is damaged, people cannot move their eyes normally. Symptoms include double vision Vision, Double Double vision is seeing two images of one object. Double vision may occur when only one eye is open (monocular diplopia) or, more commonly, when both eyes are open (binocular diplopia). Binocular... read more when looking in certain directions.
If the 3rd cranial nerve (oculomotor nerve Third Cranial Nerve (Oculomotor Nerve) Palsy A palsy of the 3rd cranial nerve can impair eye movements, the response of pupils to light, or both. These palsies can occur when pressure is put on the nerve or the nerve does not get enough... read more ) is paralyzed, people cannot raise their upper eyelid. It droops down over the eye and interferes with vision.
If the 8th cranial nerve (auditory or vestibulocochlear nerve) is damaged or malfunctions, people may have problems hearing and/or have vertigo Dizziness and Vertigo Dizziness is an inexact term people often use to describe various related sensations, including Faintness (feeling about to pass out) Light-headedness Dysequilibrium (feeling off balance or... read more —a feeling that they, their environment, or both are spinning.
Cranial nerve disorders can also cause various kinds of facial or head pain.
A doctor's evaluation
Tests of cranial nerve function
Usually magnetic resonance imaging
When doctors suspect a cranial nerve disorder, they ask the person detailed questions about the symptoms. They also test the function of the cranial nerves Cranial Nerves When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more by asking the person to do simple tasks, such as to follow a moving target with the eyes.
Imaging of the brain with magnetic resonance imaging (MRI) is often needed.
Treatment of the cause
Treatment of specific cranial nerve disorders depends on the cause.