Ultrastructural changes with age in the human superior laryngeal nerve.

Electron-microscopic morphometric techniques were used to examine age-related changes in postmortem human superior laryngeal nerves obtained at autopsy (young adult, aged 20 to 30 years; old, 60 years and over). A statistically significant age-related loss of myelinated nerve fibers was detected (old, 7032 +/- 1572; young, 10,179 +/- 1969), representing a 31% decrease. Much of this loss occurred selectively in small myelinated fibers (1 to 2 microns) where there was an extensive (67%) and significant age-related fiber loss. A corresponding analysis of axonal diameter of myelinated nerve fibers similarly showed an extensive (67%) and statistically significant decrease in myelinated fibers with small axonal diameters (0 to 0.5 microns) in the old age group compared with the young adult age group. These findings may represent a significant histomorphologic correlate to the observed age-related sensorimotor dysfunction of the upper aerodigestive tract common in the elderly.