SPINAL CORD POTENTIALS GENERATED BY IMPULSES IN MUSCLE AND CUTANEOUS AFFERENT FIBRES

Abstract

A study was made of the potentials generated in the cat''s spinal cord by volleys in the groups I, II and III muscle afferent fibers and in cutaneous afferent fibers. Potentials due to impulses in the different groups were separated by a subtraction technique depending on the differing thresholds and conduction velocities of such groups. The areas in which volleys in any one group of fibers generate focal synaptic potentials were assumed to be the areas in which this group establishes synaptic connections. In the dorsal horn and intermediate region of the 6th and 7th lumbar segments quadriceps, biceps-semitendinosus and gastrocnemius afferent fibers make synaptic connections of similar pattern. Group Ia afferent fibers relay in the intermediate nucleus. Groups Ib and II afferent fibers have relay sites more extensively distributed in any transverse section but still in the intermediate zone. Group III afferent fibers relay in the dorsal horn dorsolateral to the intermediate nucleus. Impulses in the group II and HI afferent fibers of quadriceps and biceps-semitendinosus appear to have no excitatory action on quadriceps motoneurones but excite BST motoneurones after relay in the intermediate nucleus and dorsal horn. The two fastest conducting groups of sural fibers relay in the dorsal horn dorsolateral to the intermediate nucleus. Impulses in these fibers probably do not cause excitation of quadriceps motoneurones, but impulses in the slower group excite biceps-semitendinosus motoneurones after relay in the dorsal horn.