IMPULSES IN THE ROSTRAL BRANCH OF PRIMARY AFFERENTS IN RAT DORSAL COLUMNS TRAVEL FASTER THAN THOSE IN THE CAUDAL BRANCH

Myelinated sensory afferents on entering the spinal cord form a juncti on in the dorsal columns and send a branch toward the head and another caudally. Recent experiments have shown that orthodromic impulses are reliably transmitted over the rostral branch but may suffer a transmi ssion block in the caudal branch. This paper investigates a possible r eason for the difference between rostral and caudal branches of the sa me axon bp measuring the conduction velocities in each. Axons of eithe r the ascending or descending branches of afferents in the L(1) dorsal root of rat spinal cord were stimulated in the dorsal columns at vari ous distances from the dorsal root. The resulting compound action pote ntial or single unit spikes were recorded on the L(1) dorsal root. The conduction velocity was found to be twice as fast in the rostral bran ch as in the caudal branch of the same axons.