Morphometric aspects of peripheral nerves in adults and the elderly

There have been inconsistencies among reports of age-related differences in human peripheral nerves (PNs). For such studies, normal control values are necessary. Moreover, the diversity of methods employed makes it difficult to compare results. We used the same histological procedures and methods to measure 12 PNs: 8 in the cranial nerves, 2 motor nerves in the lower limb, and 2 nerves in the autonomic system. We performed a morphometric analysis of nerve fibers and estimated the change in the total number (TN) and average transverse area (ATA) of myelinated axons from adulthood to old age. The spinal nerves demonstrated notable age-related changes in TN and ATA. Most of the cranial nerves also demonstrated notable age-related changes in TN and ATA. However, some nerves demonstrated no such age-related changes and were affected more by other factors. With regards to the autonomic nerves, the lesser splanchnic nerve indicated age-related changes in TN, but the greater splanchnic nerve indicated no age-related changes in either TN or ATA. The autonomic nerves were affected not only by the aging process but also by the pathological changes to the peripheral tissues that they innervate.