Overview of the cranial nerves

[Dave Paprocki]

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).
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 damages the area that controls the facial nerve
The nerve fibers that connect cranial nerve centers within the brain, as occurs in internuclear ophthalmoplegia
Only one cranial nerve, as occurs in oculomotor palsy, trigeminal neuralgia, Bell palsy, and hemifacial spasm

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:

3rd cranial nerve
4th cranial nerve
6th cranial nerve

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.