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Ta k e 5 a n d t r y A B M P F i v e - M i n u t e M u s c l e s a t w w w. a b m p . c o m / f i v e - m i n u t e - m u s c l e s . 39 WHAT CAUSES TRIGEMINAL NEURALGIA? Readers will remember that most of our neurons are covered by a layer of material called myelin, which serves to speed transmission and to provide electrical insulation to individual axons. In the peripheral nervous system, the myelin sheaths of the trigeminal nerve are constructed of Schwann cells that are strung like beads along the individual neurons. But as the fibers approach the brain, their covering changes from Schwann cells to the oligodendrocytes that provide myelin in the central nervous system. In this transition area, the myelin is thinner than in other locations and vulnerable to damage Physical damage to the trigeminal nerve as it approaches the pons appears to be a factor in the symptoms of TN—sometimes. Small arteries inside the skull may compress a vulnerable portion of the trigeminal nerve in a phenomenon called neurovascular conflict. This can be identified in MRI tests with good accuracy and specificity. When neurovascular conflict is present, the artery irritates the nerve and wears away at the already-thin myelin covering in the transition area. This in itself can be painful, but it also creates a situation where adjacent neurons in the trigeminal nerve now lack electrical insulation. The consequences of this situation can be dire; I will paraphrase one expert's description here: Pulsations of the arteries on the nerve's root entry zone causes demyelination of axons. This allows for the abnormal generation of spontaneous impulses and their conduction to adjacent fibers, leading to a rapid buildup of electrical activity. The result is a paroxysmal explosion of symptoms 2 (emphasis mine). But neurovascular conflict is not a complete explanation of TN, for these reasons: • Neurovascular conflict is found in only about half of people with TN symptoms. • Neurovascular conflict doesn't always cause demyelination. • TN pain persists in about 30 percent of patients after neurovascular conflict is surgically corrected. • Neurovascular conflict is frequently found during autopsies of people who never reported TN pain. Anatomy Review The trigeminal nerve, or fifth cranial nerve (CN V), is the largest cranial nerve. The superior branch of the trigeminal nerve provides sensation to the forehead and down the middle of the nose. The middle branch innervates the cheeks, maxilla, and temple. And the inferior branch carries sensory messages from the chin, mandible, and lateral parts of the face, while also providing some motor control for muscles involved with chewing and swallowing. Trigeminal nerve distribution 1 1 NEW! ABMP Pocket Pathology featuring Ruth Werner WWW.ABMP.COM/ POCKET-PATHOLOGY

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