Flexion reflex elicited by ventral root afferents in the cat.

To investigate the physiological role of ventral root afferent fibers, the ventral root was stimulated in spinal cats in an attempt to elicit the flexion reflex, a common nociceptive spinal reflex. The flexion reflex was elicited by stimulating the distal stump of the cut L7 or S1 ventral root and recorded from the proximal stump of the cut S1 ventral root. In 12 of the 14 cats studied, the flexion reflex was recorded as a compound action potential. The finding was confirmed by recording single-unit activity from 5 units in two cats. These results suggest that the ventral root afferent fibers exert a variety of physiological effects that include eliciting such spinal reflexes as the flexion reflex. The responsible fibers in the ventral root travel distally towards the dorsal root ganglion to enter the spinal cord through the dorsal root.