Experimental Brain Research

, Volume 65, Issue 2, pp 271–281 | Cite as

Reflex pathways from group II muscle afferents

1. Distribution and linkage of reflex actions to α-motoneurones
  • A. Lundberg
  • K. Malmgren
  • E. D. Schomburg
Article

Summary

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 Eccles and Lundberg (1959) 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 (Wilson and Kato 1965). 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 Eccles and Lundberg (1959) and Holmqvist and Lundberg (1961).

Key words

Low spinal cats Group II muscle afferents Motoneurones Disynaptic EPSPs Trisynaptic IPSPs 

Abbreviations

Q

Quadriceps

PBSt

posterior biceps and semitendinosus

ABSm

anterior biceps and semimembranosus

G-S

gastrocnemius and soleus

FDHL

flexor digitorum and hallucis longus

Pl

plantaris

DP

tibialis anterior and extensor digitorum longus

EDB

extensor digitorum brevis

SPM or separately, Per br and Per 1

peroneus longus, tertius and brevis together

joint

posterior nerve from knee joint

Sur

sural

Saph

saphenous

SP

skin division of superficial peroneal

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • A. Lundberg
    • 1
  • K. Malmgren
    • 1
  • E. D. Schomburg
    • 1
  1. 1.Department of PhysiologyUniversity of GöteborgGöteborgSweden

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