[Structural anatomy of cranial nerves (V, VII, VIII, IX, X)]

This study reports a review of the literature on the structural anatomy of the Vth, VIIth, VIIIth, IXth, and Xth cranial nerves, known to harbor dysfunction syndromes in humans. Because these dysfunctions are hypothesized to be caused by neurovascular conflicts at the root entry/exit zone and the transitional zone between central and peripheral myelinization, this investigation focused on the study and description of this junction. All the cranial nerves, except the optic and olfactory nerves, which are considered to be more a direct expansion of the central nervous system, have a transitional zone between central myelin (coming from oligodendrocytes) and peripheral myelin (produced by Schwann cells). The human studies reported in the literature argue in favor of a dome-shaped transitional zone directed to the periphery. It seems that this junctional region is situated more peripherally in sensory nerves than in motor nerves. The transitional zone is situated very peripherally for the cochlear and vestibular nerves, and on the contrary very close to its exit from the brain stem for the facial nerve.