Morphometric nerve fiber analysis and aging process of the human vestibular nerve

Myelinated and unmyelinated nerve fibers of the human vestibular nerve were analyzed with the use of a new staining method that makes it possible to discriminate various structures of the nervous tissue. An image-analyzing digitizer, a microscope with a drawing tube and a personal computer for storing data and performing statistical analyses were employed in this study. We measured the axonal numbers and transverse areas of myelinated vestibular nerve fibers in 20 cadavers, and of unmyelinated fibers in 14 cadavers. The average number of myelinated axons and unmyelinated axons were 20,318 and 2,782, and the average transverse area of their axons were 3.46 and 0.49 micron 2, respectively. The transverse areas of myelinated axons decreased with age, although the numbers of their axons did not change. However, in the case of unmyelinated axons, both the transverse areas and the numbers did not change.