Shared reflex pathways from Ib tendon organ afferents and Ia muscle spindle afferents in the cat (original) (raw)
1983, The Journal of Physiology
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.
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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.
Shared reflex pathways of group I afferents of different cat hind-limb muscles
The Journal of physiology, 1983
The convergence of group I muscle afferents of different muscle origin onto interneurones in spinal reflex pathways has been investigated using the technique of spatial facilitation of the transmission from afferents to motoneurones. The investigated pathways are those of non-reciprocal inhibition and of oligosynaptic excitation of motoneurones. Extensive convergence has been found of group I afferents from muscles operating at the same and different joints onto the interneurones interposed in both excitatory and inhibitory, disynaptic and trisynaptic pathways to motoneurones. Convergence has been found between muscle spindle Ia and/or tendon organ Ib afferents from different muscles, thereby extending observations on convergence of these subgroups of group I afferents from the same muscles. The results show that group I afferents of different muscles influence motoneurones via shared neuronal pathways and that transmission from these afferents is influenced by afferents originating...
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.
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.
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...
Synaptic connections from large muscle afferents to the motoneurons of various leg muscles in man
Experimental Brain Research, 1984
Cross-correlations between stimuli delivered to peripheral nerves and the discharges of single, voluntarily activated, motor units can provide information about facilitatory and inhibitory projections to single spinal motoneurons in man. The projection frequency, under the given circumstances, of a facilitatory or inhibitory pathway can be obtained from the proportion of the sampled motor units of a given muscle showing the facilitatory or inhibitory effect. Deductions about the shape and relative amplitude of the underlying post-synaptic potentials can be made from the profile of the changes in firing probability. This technique has been used to explore the projections of low threshold muscle afferents to motoneurons of various leg muscles in man. Homonymous facilitation was demonstrated to all the sampled motor unit s of soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA) and vastus medialis (VM) and is presumed to represent the effects of the composite muscle spindle group Ia EPSP. Heteronymous facilitation was demonstrated between certain synergists. The projection frequency was less and the magnitude of the change in firing probability was smaller than for homonymous facilitation. SOL motoneurons, however, were not facilitated from low threshold afterents in the medial gastrocnemius nerve. Reciprocal inhibition was demonstrated between certain antagonists. The majority of the sampled motor uni.ts of SOL, however, were facilitated from low threshold afferents in the common peroneal nerve. The threshold for this facilitation was higher than for the homonymous facilitation elicited from this nerve and thus a different class of afferents and/or intercalated interneurons may be involved. There are projections across the knee joint in man. Motor units in vastus medialis (VM) were facilitated from low threshold Offprint requests to: P. Ashby (address see above) afferents in the common peroneal nerve. It is likely that these reflex connections, which differ from those in other species, reflect the functional relationships between various lower limb muscles in man.
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'.
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