Cranial nerves are nerves that emerge directly from the brain as opposed to the spinal cord. There are 12 pairs of cranial nerves with motor and sensory functions. Problems with cranial nerves may affect a motor nerve, called a cranial nerve palsy, or affect a sensory nerve, causing pain or diminished sensation. The cause of damage may be unknown; some known causes include brain tumors, abscesses, bleeding into and around the brain, and infections.
Oculomotor Nerve Palsy
The oculumotor nerve is also known as cranial nerve III. This nerve is responsible for controlling most of the muscles of the eyes. In addition, it helps the iris to constrict, narrowing the pupil for better vision in brighter light. It also focuses the lens for close-up vision. A palsy of this nerve generally leads to the eye looking down and outward, causing double vision. The pupil will be dilated and will not focus on nearby objects.
Trigemal Neuralgia and Parry Romberg Syndrome
Trigeminal neuralgia, also known as tic douloureux, is a condition of sharp lancinating pain lasting two minutes or less that affects one side of the face. Parry Romberg syndrome causes progressive deterioration of the soft tissues and skin on one side of the face and severe pain in the areas supplied by cranial nerve V. This cranial nerve is known as the trigeminal nerve. It has both sensory and motor functions; it receives touch sensation from the face and controls the muscles of chewing.
Bell's Palsy
Bell's palsy is sudden paralysis of the facial nerve, cranial nerve VII, usually caused by herpes simplex virus infection. According to the Merck Manual Home Edition, 23 out of every 100,000 people will experience Bell's palsy at least once in their lives. Most patients who experience Bell's palsy with partial paralysis will completely recover within a few months, even without treatment. Patients who experience full paralysis have a more uncertain prognosis.
Hemifacial Spasm, Ramsay Hunt Syndrome and Melkersson–Rosenthal Syndrome
These syndromes also all affect cranial nerve VII, responsible for moving most of the muscles of the face. In the condition called hemifacial spasm, also called tic convulsif, one side of the face twitches involuntarily. Ramsay Hunt syndrome is a herpes zoster virus infection of the facial nerve that is more painful than Bell's palsy. Full recovery is likely. In Melkersson–Rosenthal syndrome, intermittent facial nerve paralysis is accompanied by facial swelling.
Vagus Nerve Damage
Cranial nerve X is called the vagus nerve. It aids in swallowing and control of the voice, and controls the automatic functions of many of the organs such as the heart and stomach. Damage to this nerve impairs swallowing, speech and function of many of the organs. It can cause a low heart rate and blood pressure, leading to vasovagal syncope, or fainting. If it is damaged at the stomach, gastroparesis may result, in which the stomach does not empty properly.
Hypoglossal Nerve Palsy
Cranial nerve XII is the hypoglossal nerve. A hypoglossal nerve palsy prevents movement of the tongue on one side. The tongue becomes weak and may begin to waste away, causing problems eating and speaking. Damage to this nerve can be caused by amyotrophic lateral sclerosis, injury or tumor, stroke, or infection. Treatment depends on the underlying cause of the palsy.
