Shared reflex pathways of group I afferents of different cat hind-limb muscles (original) (raw)
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Shared reflex pathways from Ib tendon organ afferents and Ia muscle spindle afferents in the cat
The Journal of Physiology, 1983
The possibility was investigated that group Ia muscle spindle afferents and group Ib tendon organ afferents influence spinal motoneurones via shared neuronal pathways. Mutual facilitation of actions of these afferents at a premotoneuronal level has been taken as evidence that they use the same interneurones to evoke post-synaptic potentials (p.s.p.s) in motoneurones. 2. Inhibitory p.s.p.s (i.p.s.p.s) or excitatory p.s.p.s (e.p.s.p.s) were evoked in motoneurones by selective activation of group Ia afferents or group Ib afferents. P.s.p.s following stimulation of both Ia and Ib afferents were then compared with the arithmetic sum of p.s.p.s evoked by each of them separately. When the former were larger the difference was used as a measure of synaptic actions mediated by interneurones co-excited by I a and I b afferents. 3. Both excitatory and inhibitory pathways to motoneurones have been found to be shared by Ia and I b afferents, although the proportion of interneurones actually used in common by these afferents could not be established. The latencies of post-synaptic actions mediated by such interneurones indicated that they were evoked disynaptically or trisynaptically. 4. The study leads to two main conclusions: that group I a muscle spindle afferents, and in consequence also fusimotor systems, may modulate the reflex action of tendon organs, and that the two groups of afferents are a source of information in a common feedback system.
Convergence from lb, cutaneous and joint afferents in reflex pathways to motoneurones
Brain Research, 1975
Starting out from the lengthening reaction 10 much of the interest in the proprioceptive regulation by Ib impulses from Golgi tendon organs has been centred around autogenetic inhibition 4,9. It is, however, well known that for any particular motor nucleus Ib actions are drawn from a wide receptive field consisting of many muscles. In low spinal cats the main pattern is that Ib volleys from extensors evoke IPSPs in extensor and EPSPs in flexor motoneurones 2, while the inverse myotatic pattern of high spinal cat also includes IPSPs in flexor and EPSPs in extensor motoneurones by Ib volleys from flexors 7. Interneurones of Ib reflex pathways also receive excitation from the corticospinal and rubrospinal tracts 6,8. Rubrospinal facilitation revealed more complex spinal Ib patterns than those encountered in spinal cats, also including lb inhibition of extensor motoneurones from flexors and vice versa of flexor motoneurones from extensors. These findings led to the suggestion that there are alternative spinal Ib reflex patterns and that a command for a complex movement which may include co-contraction of flexors and extensors is accompanied by mobilization of the appropriate Ib reflex pattern 6. A Ib inhibitory linkage between co-contracting muscles would be assured if lb afferents from these muscles converged on the same interneurones. We have now investigated Ib convergence on interneurones with the indirect technique of testing spatial facilitation in transmission of synaptic actions to motoneurones, excitatory convergence being indicated when the size of the PSP evoked by combined stimulation of two nerves exceeds the sum of the PSPs evoked from each nerve. It will be shown that excitatory convergence from different muscles is common on interneurones of Ib inhibitory and excitatory pathways and, furthermore, that these interneurones also receive excitatory convergence from low threshold cutaneous and joint afferents.
The Journal of Physiology, 1981
1. Inhibitory post-synaptic potentials (i.p.s.p.s) evoked by adequate stimulation ofgroup I a muscle spindle afferents oftriceps surae and plantaris and by near-threshold electrical stimulation of quadriceps and hamstring nerves were recorded in a number of motoneurone species. The aim of the study was to compare the pattern of non-reciprocal I a inhibitory actions on hind-limb motoneurones with the pattern of inhibition evoked from group Ib tendon organ afferents. 2. In all the motoneurone species analysed in which i.p.s.p.s were evoked by electrical stimulation maximal for both group I a and Ib afferents of triceps sure and plantaris, they were also evoked when these muscles were stretched and the amplitude of the stretch (10-35 jsm) was below threshold for I b afferents; 70-100 % of motoneurones with I b i.p.s.p.s showed stretch-evoked i.p.s.p.s. The stretch-evoked i.p.s.p.s appeared with latencies compatible with disynaptic and trisynaptic linkage. Since these latencies were too short to allow their mediation by group II afferents the i.p.s.p.s are attributed to a selective action of Ia afferents. The i.p.s.p.s did not appear after the nerves to triceps surae and plantaris had been cut. 3. Electrical stimulation of quadriceps and hamstring nerves which was near threshold for I a afferents and well below threshold for either the Ib component of the incoming volley or group II afferents, similarly evoked non-reciprocal i.p.s.p.s. They were found in those motoneurones in which inhibition was evoked by stimulation maximal for group I afferents. Such I a i.p.s.p.s were evoked both in homonymous motoneurones and in motoneurones of four other hind-limb muscles. Their latencies corresponded to di-and trisynaptic coupling. 4. In some motoneurones ofthe pretibial flexors (anterior tibial, extensor digitorum longus and peroneus longus), disynaptic i.p.s.p.s evoked from triceps surae and/or plantaris which were depressed by a conditioning ventral root stimulation (i.e. Ia reciprocal i.p.s.p.s) were followed by trisynaptic i.p.s.p.s which were not depressed in this way (I a 'non-reciprocal' i.p.s.p.s). It thus appears that the same motoneurones may be inhibited by impulses in group I a afferents via different spinal pathways. 5. The study leads to the conclusion that the non-reciprocal inhibition from group I a muscle spindle afferents operates in parallel with the inhibition from group Ib tendon organ afferents in all motoneurone species tested.
Reflex pathways from group II muscle afferents
Experimental Brain Research, 1987
The interneuronally mediated reflex actions evoked by electrical stimulation of group II muscle afferents in low spinal cats have been reinvestigated with intracellular recording from motoneurones to knee flexors and ankle extensors. The results of have been confirmed and extended. There was wide convergence from flexors and extensors of group II excitation to flexor and group II inhibition to extensor motoneurones. Some quantitative differences in the effect from the different nerves are described. Latency measurements suggest that the minimal linkage is disynaptic in the excitatory interneuronal pathways and trisynaptic in the inhibitory pathways. Disynaptic group II EPSPs were found in 14% of the ankle extensor motoneurones but were much more common in unanaesthetized high spinal cats . From these results and corresponding ones on flexors (Holmqvist and Lundberg 1961) it is postulated that secondary afferents in addition to the weak monosynaptic connexions (Kirkwood and Sears 1975) have disynaptic excitatory pathways and trisynaptic inhibitory pathways to both flexor and extensor motoneurones. It is proposed that the group II actions of the flexor reflex pattern characterizing the anaesthetized low spinal cat are due to suppression of the inhibitory pathway to flexor motoneurones and the excitatory pathway to extensor motoneurones. In some ankle extensor motoneurones the disynaptic group II EPSPs occurred in combination with IPSPs from the FRA (including group II and III muscle afferents). The possibility is considered that these group II EPSPs are mediated by an interneuronal group II pathway with little or no input from group III muscle afferents but probably from extramuscular receptors. In other ankle extensor motoneurones group II EPSPs were combined with EPSPs from group III muscle afferents, cutaneous afferents and joint afferents. It is postulated that these group II EPSPs are mediated by an interneuronal pathway from the FRA which also supply interneuronal pathways giving inhibition to extensor or/and flexor motoneurones and excitation to flexors as postulated by and .
Experimental Brain Research, 1969
1. The effect of stimulation of the red nucleus on transmission of synaptie actions from different systems of primary afferents to alpha motoneurones has been invest/gated in cats, mainly with intracellular recording from motoneurones. 2. The dominating effect is facilitation, presumably caused by excitatory action exerted from the rubrospinal tract on interneurones of reflex arcs. The time course of facilitation suggests that the minimal linkage from the rubrospinal tract to these interneurones is monosynaptic. 3. Interneuronal transmission in reflex pathways from the following afferent systems is facilitated : a) Ia inhibitory between flexors and extensors, l~ubrospina] facilitation did not reveal Ia inhibitory pathways between adductors and abductors at the hip. b) Ib excitatory and inhibitory. There is marked facilitation of the reciprocal effects evoked by Ib afferents from extensors but also of other Ib pathways, for example inhibitory from extensors to flexor nuclei and from flexors to extensor nuclei and excitatory from flexors to extensor nuclei, e) Low threshold joint, inhibitory and excitatory, presumably from afferents with Ruffini endings. d) Low threshold cutaneous, excitatory and inhibitory. Since transmission from these afferents could be facilitated under conditions when there was no effect on transmission from high threshold muscle afferents it is postulated that the effect is exerted on pathways which are not part of the common pathways from the flexor reflex afferents, e) Flexor reflex afferents, excitatory and inhibitory. Facilitation of these pathways is not found regularly, in some eases there was no effect and in others inhibition. 4. The effeets are discussed in relation to the complex effects evoked from the rnbrospinal tract in motoneurones and to supraspinal regulation of proprioceptive reflexes. 5. It is postulated that in complex movements alternative Ib patterns may be mobilized, whereas flexion-extension movements are subserved by the Ib pattern found in the spinal eat. 6. Facilitation of the Ia inhibitory pathway is taken to indicate "a-y-linkage" in reciprocal inhibition. It is pointed out that convergence from Ia and descending impulses on a common inhibitory interneurone may play an important role in the regulation of a-y-linked flexion-extension movements.
The Journal of physiology, 1983
A hypothesis has been verified that laminae V-VI interneurones which mediate non-reciprocal inhibition of motoneurones from group I muscle afferents have collateral actions on other laminae V-VI interneurones. Stimulation within the areas of projection of these inhibitory interneurones in motor nuclei and in Clarke's column would be expected to give rise to monosynaptic i.p.s.p.s in interneurones with disynaptic i.p.s.p.s from group I afferents if the hypothesis were correct. Intracellular records were made from eighty-five laminae V-VI interneurones with input from group Ia muscle spindle and/or group Ib tendon organ afferents. Weak intraspinal stimuli applied in motor nuclei in L7 and S1 segments, or in the lateral funiculus just caudal to Clarke's column in L4, were found to evoke monosynaptic i.p.s.p.s in seventy-two interneurones. These i.p.s.p.s were systematically correlated with disynaptic inhibition from group Ia or Ib afferents but not from other fibres. Such monos...
Characteristics of the excitatory pathway from group II muscle afferents to alpha motoneurones
Brain Research, 1975
An understanding of the role of secondary spindle afferents in motor regulation requires more detailed information regarding their segmental effects. It has recently been shown that secondary afferents terminate not only in the dorsal horn but also in the ventral horn close to the motor nuclei 4,5. For the assessment of the linkage of synaptic effects evoked from these afferents, it is important that there is a considerable slowing down of the conduction velocity in the spinal cord and thus that the intraspinal conduction time can contribute significantly to the central delay a.
European Journal of Neuroscience, 2010
A first step towards understanding the operation of a neural network is identification of the populations of neurons that contribute to it. Our aim here is to reassess the basis for subdivision of adult mammalian spinal interneurons that mediate reflex actions from tendon organs (group Ib afferents) and muscle spindle secondary endings (group II afferents) into separate populations. Reexamining the existing experimental data, we find no compelling reasons to consider intermediate zone interneurons with input from group Ib afferents to be distinct from those co-excited by group II afferents. Similar patterns of distributed input have been found in subpopulations that project ipsilaterally, contralaterally or bilaterally, and in both excitatory and inhibitory interneurons; differences in input from group I and II afferents to individual interneurons showed intra-rather than inter-population variation. Patterns of reflex actions evoked from group Ib and II afferents and task-dependent changes in these actions, e.g. during locomotion, may likewise be compatible with mediation by premotor interneurons integrating information from both group I and II afferents. Pathological changes after injuries of the central nervous system in humans and the lineage of different subclasses of embryonic interneurons may therefore be analyzed without need to consider subdivision of adult intermediate zone interneurons into subpopulations with group Ib or group II input. We propose renaming these neurons 'group I ⁄ II interneurons'.