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Overview of the Cranial Nerves> >
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
A cranial nerve disorder may result when the following are damaged or malfunction:
The nerve fibers that connect cranial nerve centers within the brain, as occurs in internuclear ophthalmoplegia (see Internuclear Ophthalmoplegia)
Areas of the brain that control cranial nerves (called centers, or nuclei), as may occur when a stroke damages the area that controls the facial nerve (see Overview of Stroke : Symptoms)
Disorders that directly damage cranial nerves include injuries, tumors, inflammation, infections (such as shingles), an inadequate blood supply (as occurs in diabetes), drugs, and toxins.
Symptoms 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 one of the 2nd cranial nerves (optic nerve) is damaged, the affected eye is blind (see Optic Nerve Disorders).
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 (see Palsies of Cranial Nerves That Control Eye Movement). Symptoms include double vision when looking in certain directions.
If the 3rd cranial nerve (oculomotor nerve) is paralyzed, the upper eyelid is paralyzed. It droops down over the eye and interferes with vision (see Third Cranial Nerve (Oculomotor Nerve) Palsy).
The 8th cranial nerve (vestibulocochlear nerve) controls balance. If this nerve is damaged or malfunctions, people may have vertigo (see Dizziness and Vertigo)—a feeling that they, their environment, or both are spinning.
Cranial nerve disorders can also cause various kinds of facial or head pain.
When doctors suspect a cranial nerve disorder, they ask the person detailed questions about the symptoms and test the function of a cranial nerve 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) or computed tomography (CT) is often needed.
Testing Cranial Nerves
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