Sensory fibres in ventral roots L7 and Si in the cat.

1. Receptive fields were determined for ninety-eight unmyelinated and 132 myelinated axons in the L7 and S1 cat ventral roots.2. Seventy of the ninety-eight unmyelinated axons had their receptive fields in somatic structures, the skin and deep tissues.3. Of the seventy unmyelinated axons with somatic receptive fields, thirty-five were mechanical nociceptors, fifteen were mechanical and thermal nociceptors, eleven were deep nociceptors, six were thermal receptors, and three were low threshold mechanoceptors.4. Twenty-four of the ninety-eight unmyelinated axons had their receptive fields in visceral structures: the intestine, bladder and vagina.5. We confirm the work of others that myelinated fibres attached to peripheral receptive fields can be found in ventral roots and that the receptive fields and functional qualities of these fibres are as one would expect of dorsal root fibres for the same segments.6. A previous study demonstrated that approximately 30% of the axons in the L7 and S1 cat ventral roots are unmyelinated and arise from dorsal root ganglion cells. The present study confirms that these axons are sensory and that the axons are predominantly cutaneous nociceptors and visceral afferents. Thus it is concluded that the L7 and S1 cat ventral roots have a major sensory component.