Comments on reflex actions evoked by electrical stimulation of group II muscle afferents (original) (raw)
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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.
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 .
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.
Group I Disynaptic Excitation in Flexor and Bifunctional Motoneurons during Locomotion
Annals of The New York Academy of Sciences, 1998
I n the absence of locomotion, activation of extensor muscle spindle (Ia) and tendon organ (Ib) afferents evokes a widespread pattern of interneuronally mediated inhibition and excitation through the nonreciprocal reflex systems. 1 During the extension phase of fictive locomotion, however, the same afferents evoke a disynaptic excitation of extensor motoneurons. Recently it has been reported that stimulation of flexor group I afferents also evokes a locomotor-dependent excitation of ankle flexor motoneurons. The present study further examined the distribution of locomotor-dependent group I excitation of flexor motoneurons and extended the analysis to motoneurons showing complex patterns of depolarization during locomotion, that is, motoneurons innervating bifunctional muscles. Intracellular recordings of antidromically identified motoneurons were made (using glass microelectrodes filled with QX-314 to block action potentials) in decerebrate cats in which fictive locomotion was elicited by brainstem stimulation following neuromuscular blockade (see reference 2).
Monosynaptic EPSPs in primate lumbar motoneurons
Journal of Neurophysiology, 1993
1. Homonymous and heteronymous monosynaptic composite excitatory postsynaptic potentials (EPSPs) were evaluated by intracellular recordings from 89 motoneurons innervating triceps surae (n = 59) and more distal (n = 30) muscles in 14 pentobarbital-anesthetized monkeys (Macaca nemestrina). 2. Homonymous EPSPs were found in all motoneurons tested. The mean values +/- SD for maximum EPSP amplitude of triceps surae motoneurons were 2.5 +/- 1.3, 1.8 +/- 1.3 and 4.5 +/- 2.0 mV for medial gastrocnemius, lateral gastrocnemius, and soleus motoneurons, respectively. Heteronymous EPSPs were almost always smaller than their corresponding homonymous EPSPs. 3. Triceps surae EPSP amplitude was larger in motoneurons with higher input resistance. However, this relationship was weak, suggesting that factors related to input resistance play a limited role in determining the magnitude of the EPSP. 4. The mean ratio +/- SD of the amplitude of the EPSP elicited by combined stimulation of all triceps sura...
Depression of group Ia monosynaptic EPSPs in cat hindlimb motoneurones during fictive locomotion
The Journal of Physiology, 2000
The monosynaptic excitation of homonymous and synergistic hindlimb motoneurones following activation of group Ia muscle spindle afferents (e.g. Eccles et al. 1957) is considered to be a fundamental component of postural regulation. Accordingly, muscle stretch during movements such as locomotion activates group Ia afferents which, by monosynaptically exciting motoneurones, produces muscle contraction to counter muscle lengthening (see Lundberg, 1969). The gain of this simple reflex depends upon both motoneurone excitability and the strength of synaptic transmission between afferents and motoneurones. Phasic changes in the amplitude of monosynaptic reflexes during locomotion have been reported in a number of studies in man and cat (see Brooke et al. 1997). Since motoneurones are subject to a rhythmic depolarization during locomotion, it is not surprising that monosynaptic reflexes are larger in the locomotor phase in which the motoneurones are actively depolarized (Akazawa et al. 1982). However, in addition to a phasic reflex modulation between the locomotor phases, the gain of the monosynaptic reflex during locomotion is tonically reduced compared to non-locomotor conditions in cat (Bennett et al. 1996) and in man (Capaday & Stein, 1986; Faist et al. 1996; Andersen & Sinkjaer, 1999). There is no evidence for the emergence of an inhibitory postsynaptic component of the monosynaptic EPSP that might account for the decrease in reflex gain during locomotion. On the contrary, intracellular recordings reveal an additional disynaptic excitatory component of the monosynaptic EPSP
The Journal of physiology, 1996
1. Intracellular recording from extensor motoneurones in paralysed decerebrate cats was used to examine the distribution of short-latency non-monosynaptic excitation by group I afferents during fictive locomotion produced by stimulation of the mesencephalic locomotor region (MLR). 2. During the extension but not the flexion phase of fictive locomotion, stimulation of ankle extensor nerves at 1.2-2.0 times threshold evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating hip, knee and ankle extensors. Disynaptic EPSPs were also evoked by selective activation of group Ia muscle spindle afferents by muscle stretch. 3. The central latencies of these group I-evoked EPSPs (mean, 1.55 ms) suggest their mediation by a disynaptic pathway with a single interneurone interposed between extensor group I afferents and extensor motoneurones. Disynaptic EPSPs were also evoked during periods of spontaneous locomotion following the cessation of MLR stimulation. 4. Hip extensor m...