A quantitative study of nerve fibers in the human facial nerve.

The facial and intermediate nerves were quantitatively evaluated in seven patients who died from systemic malignancies not involving the facial nerve. In addition, five of the specimens were also qualitatively evaluated by measuring the total and axon diameters of the facial and intermediate nerve fibers. In two cases the facial nerve fibers were counted at five different levels. The total number of myelinated nerve fibers in the facial nerve varied from 7500 to 9370. The total number of myelinated nerve fibers in the intermediate nerve varied between 3120 and 5360. The peak diameter of the facial nerve axon was between 4 and 6 microns, and was between 2 and 3 microns in the intermediate nerve. When comparing nerve segments at different anatomical levels, the largest amount of nerve fibers was found at the level of the middle mastoid portion. However, this number did not reach the amount of nerve fibers counted in the internal acoustic meatus.