LUMBAR MOTONEURONS OF MAN IITHE NUMBER AND DIAMETER DISTRIBUTION OF LARGE- AND INTERMEDIATEhyphen;DIAMETER CYTONS IN ldquo;MOTONEURON COLUMNSrdquo; OF SPINAL CORD OF MAN

摘要

Using a methodology which corrects for split cell error, and for the linear relationship between diameter of nucleolus and of cell body (cyton) and using semi-automatic methods of counting and sizing and programmed calculation and plotting, the number and diameter histograms of cytons of L-3, L-4, and L-5 motoneuron columns of 18 reference spinal cords of man (ages 17 to 82 years) have been evaluated. The number and frequency distribution of diameters (diameter histograms) of myelinated fibers of L-3, L-4 and L-5 ventral spinal roots (VSRs) had been determined in a preceding study as a control to validate the estimated number of alpha and gamma motoneuron cytons determined in this study from the same segment of spinal cord. The diameter histograms of cytons of motoneuron columns consistently contain three discrete peaks: a large-diameter peak (CL), an intermediate-diameter (CI) and small-diameter peak (CS). To illustrate, on the average, there were 4874 plusmn; 585 large cytons and 1700 plusmn; 564 rarr; intermediate cytons in the L5 segment of spinal cord. A reasonably close concordance was found between the average number of large cytons of spinal cord segments and the number of large-diameter myelinated fibers of ventral spinal roots (VSRs) (0.91, 0.94, and 0.98 for L3, L4 and L5 spinal cord segments and ventral spinal roots, respectively). For the ratio of the number of intermediate cytons to the number of intermediate axons the concordance was not as good (0.77, 0.85, and 1.14 for L3, L4 and L5 segments, respectively). Assuming that a cyton provides only one axon to VSR it is reasonable to infer from our studies that most large-diameter cytons are those of alpha motoneurons and that most of the intermediate-diameter cytons are those of gamma motor neurons. The greater number of axons than of cytons for the intermediate diameter group may be from a spurious inclusion of small-diameter axons (possibly pre-ganglionic autonomic fibers) with the intermediate-diameter group. On the average, the range of diameters of large-diameter cyton population in motoneuron col