Nerves

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Typography

There are 12 cranial nerves in the human body. Unlike most of the nerves in our bodies, the cranial nerves originate from the brain itself (specifically from the brain stem), not the spinal cord. Some, like the trigeminal and facial nerves, exit through the skull and run between the skull and skin. Others, for example nerves to the eyes, ears, and nose, remain completely within the skull, neck, or chest. Here is a list of these nerves, numbered I through XII:

I – olfactory nerve – responsible for the sense of smell

II – optic – responsible for vision

III – oculomotor – controls some eye movements and dilation/constriction of the pupil

IV – trochlear – other eye movements

V – trigeminal – largest cranial nerve, responsible for facial sensation. Has 3 branches – ophthalmic, maxillary, and mandibular

VI – abducens – still more eye movements

VII – facial – controls facial movement. Viral infections of this nerve cause Bell’s palsy

VIII – vestibulocochlear – responsible for hearing and balance. Malfunction of this nerve may cause tinnitus or dizziness

IX – glossopharyngeal – controls swallowing, taste, and saliva production

X – vagus – partially controls breathing and heart rate/rhythm

XI – accessory – controls head and neck movement

XII – hypoglossal – controls tongue movement and partially responsible for speech and swallowing

As you can imagine, injury, infection, or damage to these nerves may cause a myriad of diseases and maladies, not the least of which may be blindness or deafness. One of the more painful and difficult to treat conditions involving the cranial nerves is called trigeminal neuralgia (TN). Traditionally called tic douloureux, TN is a chronic neuropathic pain disorder characterized by spontaneous or elicited paroxysms of electric shock-like or stabbing pain in a region of the face. A poor quality-of-life and suicide in severe cases has been attributed to this disorder. The pain of TN most frequently affects the distribution of the second/maxillary (cheek), or third/mandibular (jaw) branches of the nerve but may include the first/ophthalmic (orbit) branch. The diagnosis is clinical and is based on three main criteria: pain is restricted to one or more branches of the trigeminal nerve; paroxysms of pain that are sudden, intense, and very short (< one second up to two minutes) and described as a “shock” or “electric sensation”; and pain triggered by innocuous stimuli on the face or mouth. TN is almost always one-sided. The pain of TN may be triggered by common occurrences of daily life such as the touch of a napkin or gentle breeze flowing across the sensitive area of the face.

There are three types of TN – classical, secondary, and idiopathic. The classical type, which is the most common type, is caused by compression of the nerve by an enlarged artery within the brain. The secondary type, about 15% of cases, is attributable to an identifiable neurologic disease such as multiple sclerosis or a brain tumor. In the idiopathic type, about 10% of cases, there is no known cause. The classical type may be treated using a vascular surgery procedure within the brain. Otherwise, the mainstays of treatment are anti-epileptic medications like carbamazepine and oxcarbazepine. Other medications such as gabapentin, pregabalin, and antidepressants have had some success. In short, trigeminal neuralgia is an extremely painful condition that can be difficult to diagnose and treat.

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 By Peter Galvin, MD

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