Bilateral projection of neurones of the C6 segment to S1 and S2 segments of the spinal cord in the cat

Abstract

Sacral projections of neurones located in the C6 segment of the spinal cord were electrophysiologically investigated in alpha-chloralose anaesthetized cats. The cell bodies were found mainly in lamina VIII and in the ventromedial part of lamina VII of the C6 segment. At the thoracic level their axons descended in lateral funiculi, mostly on both sides and only exceptionally contra- or ipsilaterally. However, bilateral projection to sacral segments was less frequent (25 neurones). It is concluded that axons terminate at different levels on both sides of the spinal cord and only part of them project bilaterally to S1/S2 segments. Conduction velocities calculated for all the axons varied from 38 to 80 m/s and were significantly slower for their distal parts. Therefore it is suggested that descending axons send collaterals at various spinal levels. The presented data indicate the importance of these neurones for interlimb coordination.