The numbers of limb motor neurones in the individual segments of the human lumbosacral spinal cord

Abstract

The numbers of limb motor neurones in the individual segments of the human lumbosacral spinal cord of 6 previously normal subjects aged from 15 to 50 years are described. Between 93% and 99% of such neurones occur in segments L2 to S2, and 74% to 84% in L3 to S1. L1 always contains some limb motor neurones, but the numbers vary greatly from case to case as does the level of the segment at which they first appear. L5 usually contains the highest number of neurones though in one case the largest number was present in L3. The biggest concentration of neurones per section is seen in S1. The numbers of neurones on the left and right sides are similar over the lumbosacral enlargement, but may vary considerably in individual segments, particularly in the proximal and distal segments. In an individual section at any level, up to 3 times as many neurones may be seen on one side as the other.