Summary
The convergence of group II muscle afferents on interneurones in reflex pathways has been elucidated by investigating interaction in transmission to motoneurones. Recording was also made from interneurones activated from group II afferents. Maximal group II EPSPs evoked in motoneurones from different muscles (extensors or flexors and extensors) did not summate linearly but with a deficit of 35–40%. The corresponding deficit in summation with Ia EPSPs was 7%. It is suggested that the difference in deficit is caused largely by occlusion due to shared interneuronal discharge zones and that it gives an approximate minimal measure of the convergence of group II afferents from different muscles on the interneurones. Tests with weak group II volleys from different muscles gave no or little evidence for spatial facilitation in the disynaptic excitatory pathway to flexor motoneurones, and there was no or little temporal facilitation of transmission in this pathway. It is suggested that group II excitation of the interneurones in this pathway depends on few afferents giving large unitary EPSPs. Convergence of cutaneous afferents and joint afferents on the interneurones was evidenced by spatial facilitation from these afferents of group II transmission to motoneurones. Convergence on interneurones in the trisynaptic inhibitory pathway from group II afferents to extensor motoneurones was also investigated with the spatial facilitation technique. There was convergence on common interneurones of group II afferents from different muscles (extensors or flexors and extensors) and from cutaneous afferents as well as joint afferents. Trisynaptic group II IPSPs, including those depending on spatial facilitation from different muscles were resistant to recurrent depression from motor axon collaterals and are therefore not mediated by the reciprocal Ia inhibitory pathway. Interneurones with monosynaptic group II EPSPs were recorded from in the dorsal horn and intermediate region. Graded stimulation revealed large unitary EPSPs from few group II afferents. The EPSP evoked by a single group II afferent may produce firing (extracellular recording). Convergence of monosynaptic group II EPSPs from different muscles was rather limited but could be from flexors and extensors. Extensive multisensory convergence onto some of these interneurones was indicated by di-or polysynaptic EPSPs from group II and III muscle afferents, from joint afferents and from cutaneous afferents. The discussion of the functional role of the group II reflex pathways is based on previous findings suggesting the existence of alternative pathways to both flexors and extensors and demonstrating that the reciprocity of the spinal state is not obligatorily under control from the brain (Holmqvist and Lundberg 1961). It is postulated that the excitatory group II pathways mediate commands from the brain for movements engaging flexors and/or extensors and that group II inhibition may contribute spatial selectivity by lateral inhibition.
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References
Baldissera F, Hultborn H, Illert M (1981) Integration in spinal neuronal systems. In: Brooks VB (ed) Handbook of physiology, Sect I. The nervous system, Vol II. Motor control. Am Physiol Soc, Bethesda MD, pp 509–595
Behrends T, Schomburg ED, Steffens H, (1983a) Group II muscle afferents and low threshold mechanoreceptive skin afferents converging onto interneurons in a common reflex pathway to α-motoneurons. Brain Res 265: 125–128
Behrends T, Schomburg ED, Steffens H (1983b) Facilitation of segmental reflex pathways by noxious skin stimulation of the cat's hindpaw. Neurosci Lett [Suppl] 14: S23
Brink E, Jankowska E, McCrea DA, Skoog B (1983) Inhibitory interactions between interneurones in reflex pathways from group Ia and group Ib afferents in the cat. J Physiol (Lond) 343: 361–373
Eccles RM, Lundberg A (1959) Synaptic actions in motoneurones by afferents which may evoke the flexion reflex. Arch Ital Biol 97: 199–221
Fedina L, Hultborn H (1972) Facilitation from ipsilateral primary afferents of interneuronal transmission in the Ia inhibitory pathway to motoneurones. Acta Physiol Scand 86: 59–81
Fedina L, Hultborn H, Illert M (1975) Facilitation from contralateral primary afferents of interneuronal transmission in the Ia inhibitory pathway to motoneurones. Acta Physiol Scand 94: 198–221
Fournier E, Katz R, Pierrot-Deseilligny E (1983) Descending control of reflex pathways in the production of voluntary isolated movements in man. Brain Res 288: 375–377
Fu TC, Schomburg ED (1974) Electrophysiological investigation of the projection of secondary muscle spindle afferents in the cat spinal cord. Acta Physiol Scand 91: 314–329
Fu TC, Santini M, Schomburg ED (1974) Characteristics and distribution of spinal focal synaptic potentials generated by group II muscle afferents. Acta Physiol Scand 91: 298–313
Fukushima K, Kato M (1975) Spinal interneurons responding to group II muscle afferent fibers in the cat. Brain Res 90: 307–312
Harrison PJ, Jankowska E, Johannisson T (1983) Shared reflex pathways of group I afferents of different cat hind-limb muscles. J Physiol (Lond) 338: 113–127
Holmqvist B, Lundberg A (1961) Differential supraspinal control of synaptic actions evoked by volleys in the flexion reflex afferents in alpha motoneurones. Acta Physiol Scand 54 [Suppl 186]
Hongo T, Jankowska E, Lundberg A (1966) Convergence of excitatory and inhibitory action on interneurones in the lumbosacral cord. Exp Brain Res 1: 338–358
Hultborn H (1972) Convergence on interneurones in the reciprocal Ia inhibitory pathway to motoneurones. Acta Physiol Scand 85 [Suppl 375]: 1–42
Hultborn H, Illert M, Santini M (1976) Convergence on interneurons mediating the reciprocal Ia inhibition of moto-neurons. I. Disynaptic Ia inhibition of Ia inhibitory interneurones. Acta Physiol Scand 96: 193–201
Hultborn H, Jankowska E, Lindström S (1971) Recurrent inhibition from motor axon collaterals of transmission in the Ia inhibitory pathway to motoneurones. J Physiol (Lond) 215: 591–612
Hultborn H, Udo M (1972) Convergence of large muscle spindle (Ia) afferents at interneuronal level in the reciprocal Ia inhibitory pathway to motoneurones. Acta Physiol Scand 84: 493–499
Kniffki K-D, Schomburg ED, Steffens H (1981) Convergence in segmental reflex pathways from fine muscle afferents and cutaneous or group II muscle afferents to α-motoneurones. Brain Res 218: 342–346
Lundberg A (1970) The excitatory control of the Ia inhibitory pathway. In: Andersen P, Jansen JKS (eds) Excitatory synaptic mechanisms. Universitetsforlaget, Oslo, pp 333–340
Lundberg A (1979) Multisensory control of spinal reflex pathways. In: Granit R, Pompeiano O (eds) Reflex control of posture and movement. Prog Brain Res 50: 11–28
Lundberg A, Voorhoeve P (1962) Effects from the pyramidal tract on spinal reflex arcs. Acta Physiol Scand 56: 201–219
Lundberg A, Malmgren K, Schomburg ED (1975a) Convergence from Ib, cutaneous and joint afferents in reflex pathways to motoneurones. Brain Res 87: 81–84
Lundberg A, Malmgren K, Schomburg ED (1975b) Characteristics of the excitatory pathway from group II muscle afferents to alpha motoneurones. Brain Res 88: 538–542
Lundberg A, Malmgren K, Schomburg ED (1975c) Group II excitation in motoneurones and double sensory innervation of extensor digitorum brevis. Acta Physiol Scand 94: 398–400
Lundberg A, Malmgren K, Schomburg ED (1978) Role of joint afferents in motor control exemplified by effects on reflex pathways from Ib afferents. J Physiol (Lond) 284: 327–343
Lundberg A, Malmgren K, Schomburg ED (1987a) Reflex pathways from group II muscle afferents. 1. Distribution and linkage of reflex actions to α-motoneurones. Exp Brain Res 65: 271–281
Lundberg A, Malmgren K, Schomburg ED (1987b) Reflex pathways from group II muscle afferents. 3. Secondary spindle afferents and the FRA: a new hypothesis. Exp Brain Res 65: 294–306
Sherrington CS (1906) The integrative action of the nervous system. Yale University Press, New Haven London
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This work was supported by the Swedish Medical Research Council (project no. 94)
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Lundberg, A., Malmgren, K. & Schomburg, E.D. Reflex pathways from group II muscle afferents. Exp Brain Res 65, 282–293 (1987). https://doi.org/10.1007/BF00236300
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DOI: https://doi.org/10.1007/BF00236300