Actions on gamma‐motoneurones elicited by electrical stimulation of group I muscle afferent fibres in the hind limb of the cat.

Publisher Website
Google Scholar
Abstract
The reflex actions elicited by graded electrical stimulation of hindlimb muscle, skin and joint nerves were studied in an extended series of experiments in extra- and intracellular recordings from 120 lumbar .gamma.-motoneurons of cats anesthetized with chloralose. The action of group I muscle afferent fibers was examined in 95 .gamma.-cells. Of the .gamma.-cells, 83% were classified as either static or dynamic by stimulation in the mesencephalic area for dynamic control. The general responsiveness (i.e., number of input nerves with effect/number of input nerves tested) of the cells was very high (89.9%). The responsiveness to stimulation of group I muscle afferent fibers was extremely low, both in flexor and extensor .gamma.-motoneurons, irrespective of whether they were static or dynamic. There was no difference, as regards the low incidence of group I muscle reflex action, between stimulation of autogenetic and heteronymous nerves. Among the rare reflex effects elicited from group I muscle fibers, inhibition was 4 times as frequent as excitation. Inhibitory effects could be provoked from the autogenetic as well as from the heteronymous nerves. Excitatory effects were almost always autogenetic. The scarcity of group I muscle action on .gamma.-motoneurons is in striking contrast to the well-known and powerful reflex actions of Ia and Ib fibers on .alpha.-motoneurons. These findings are discussed in relation to the concept of .alpha.-.gamma. linkages, and skeletomotor and fusimotor activity cannot be rigidly linked under all conditions.