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

Abstract

SUMMARY1. The reflex actions evoked by electrical stimulation of group III muscle afferent fibres were investigated with micro-electrode recordings from ninety-three ymotoneurones projecting to hind-limb muscles of cats anaesthetized with chloralose. For seventy-eight of the ninety-three y-cells the frequency of occurrence and types of effects mediated via group II and group III muscle fibres were compared.2. Seventy-seven of the cells tested at intensities which excited group III and seventy-five of the cells tested at intensities which excited both group II and group III afferent fibres were classified as either static or dynamic, using the method of mesencephalic stimulation (Appelberg, 1981).3. The responsiveness of the whole sample of y-motoneurones to inputs from group III muscle fibres was high and comparable to that found with group II fibres.4. It was found that group III muscle fibres acted preferentially on static y-motoneurones. In contrast, group II fibres acted preferentially on dynamic y-motoneurones.5. Both excitatory and inhibitory effects were provoked by stimulation of group III fibres. Generally excitation was more frequent than inhibition.6. A strong dominance of excitation over inhibition was found in flexor muscles, and a weaker prevalence of excitation was also encountered in extensor muscles. This prevalence of excitation in extensor y-motoneurones is in contrast to the striking predominance ofgroup III-evoked inhibition ofextensor a-motoneurones as described by the flexion reflex afferents concept. 7. A comparative survey is also given of the patterns of responses elicited in individual posterior biceps-semitendinosus and gastrocnemius-soleus y-cells by stimulation of group II and group III fibres. These data further corroborate the view that reflexes from high-threshold muscle afferent fibres to y-motoneurones are organized differently from those to a-motoneurones.8. The functional implications of these findings are discussed. It is proposed that the pools of y-motoneurones should be considered as integrative systems intercalated

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

“…Interestingly, the same cells were also targets of muscle group I inhibition (see Appelberg et al 1983a, Fig. 4A), and from high-threshold muscle (Appelberg et al 1983b), skin and joint afferents inhibitory effects prevailed as well.…”

“…All the responses described in the following occurred at relatively short latencies, well below the minimal group IV latency (for details see Appelberg et al 1983b (comprising d.p., the branches to peroneus brevis, to peroneus tertius, to extensor digitorum brevis and the deep peroneal cutaneous branch); f.d.l., flexor digitorum et hallucis longus (nerve or muscle); f.r.a., flexion reflex afferents; g.s., gastrocnemius and soleus (triceps) (nerve or muscle); N, non-classified y-cell; p.b.s.t., posterior biceps and semitendinosus (nerves or muscles); Q., quadriceps (nerve or muscle); S, static y-cell; T, threshold; Tib., tibial nerve or muscle. It should be stressed that for all four categories the occurrence of a group II contribution to an observed reflex effect was clearly established, and that it was only its relative size, compared with any concomitant group III action, that varied.…”

Interpretation of fusimotor activity in cat masseter nerve during reflex jaw movements.

“…It would therefore be inappropriate for them to be modulated rapidly during fast cyclic movements in parallel with the a-motoneurones. Recent studies of y-motoneurone reflexes (Appelberg, Hulliger, Johansson & Sojka, 1983) also emphasize the relatively greater independence of dynamic fusimotor than static fusimotor neurones from a-motoneurones.…”

“…Thus the interpretation offered for fusimotor action in reflex jaw movements is that the dynamic system provides 'parameter' control as visualized by Matthews (1981), while the static system generally provides a pattern of the intended movement, described as a 'temporal template'. This would mean that the static firing profile would generally resemble that of a activity, but the very different reflex connectivity of the two systems will cause frequent departures from a firm a-y co-activation (see also Appelberg et al 1983). This scheme does not reject the idea that 'servo-assistance' is in operation, though it has usually been taken that this requires the net spindle afferent firing to be kept constant.…”

Experimental knee joint pain during strength training and muscle strength gain in healthy subjects: A randomized controlled trial

“…First, the "vicious cycle" theory hypothesizes that pain may increase muscle activity (32) and both animal and human data suggest that stimulation of group III and IV afferents excite ␥ motoneurons and thereby increase the sensitivity of muscle spindles (16,33,34). This could theoretically increase muscle activity, leading to greater contraction force during training with pain in the intervention group.…”