Nerve fiber analysis of the facial nerve.

Nerve fiber analyses were conducted on the human facial nerve with use of a new staining method (Luxol-PAS-hematoxylin stain; discriminative staining method) that permits simultaneous observation of the axon and surrounding myelin sheath. The following combination of equipment was employed in the study: an image-analyzing digitizer, a microscope with a drawing tube, and a computer for storing the data and performing statistical analyses. The numbers, transverse areas, and circularity ratios of axons were measured in 11 cases. The average number of axons composing one facial nerve was 6,254, and the average size of the axons was 6.23 microns 2. The results indicated that although the numbers of axons became reduced with age, the transverse areas and circularity ratios of the axons did not change with age.