A study of motoneuron groups and motor columns of the human spinal cord.

Eight normal human spinal cords were studied for motoneuron (Mn) groups and columns. Spinal segments (C1 to Coc.) were identified and embedded in paraffin wax. Serial cross sections were cut at 25 microm and stained by cresyl violet. Cross-sectional profiles of the spinal cord were traced for each segmental level and the outlines of the various Mn groups superimposed. These charts (maps) were used to examine intra and intersegmental changes in the relative positions of the columns. An attempt was made to provide topographical picture of Mn groups of individual segments. In the cervical region neuronal groups were more numerous but smaller and less distinct, while in the lumbosacral region they were fewer, larger and at many levels better circumscribed. The average number of Mn groups at any segmental level was 3-4 and never exceeded 5. C4, C5, C6, C7, L4, L5 and S1 contained numerous Mn groups. Maximum intrasegmental changes were noted at C3, C4, C7, T1, and S2, while at C5, C6, all thoracic, L1 L2 and L3, the pattern was constant throughout the segment. Eleven motor columns were traced in the human spinal cord. Column 1 belonged to the medial division and columns 2-11 to the lateral division of the ventral grey horn. Columns 1 and 2 were the most extensive as they were traceable from the lower medulla to S3 segment. Columns 3-8 were confined to cervical segments (including T1), while columns 9-11 were traced in lumbosacral segments. In general, motor columns followed a definite mode for their appearance and disappearance. Many of them showed rotation from a dorsal to a ventromedial direction.