Numerical size variability in the peripheral nerve

Cross-sections of 17 sciatic nerves were examined by an image analyzer as to sum of fibre carrying cross-sectional areas and by light-microscopic visual area sampling as to myelinated and unmyelinated fibre densities. Intra-perineural cross-sectional areas range from 3.5 x 10(6) to 7.6 x 10(6) micron2 with a mean of 5.8 x 10(6) in the 12 male subjects and 3.4 x 10(6) to 4.0 x 10(6), means = 3.7 x 10(6) micron2 in 4 mature females. Estimates of total fibre content range from 6.1 x 10(4) to 1.6 x 10(5) in the males and 6.1 x 10(4) to 9.2 x 10(4) in these female subjects. Variations in axon number totals and in ratios of myelinated to unmyelinated fibre densities are not age correlated. Variations also occur in the diameter distributions of myelinated fibres and in ratios of small to large diameter myelinated fibres.