Experimental Brain Research

, Volume 76, Issue 1, pp 223–228 | Cite as

Projections of group Ia afferents to motoneurons of thigh muscles in man

  • A. Bayoumi
  • P. Ashby


Changes in the firing probability of single motor units in response to electrical stimulation of muscle nerves and to tendon taps were used to derive the projections of large muscle afferents to the motoneurons of various thigh muscles in man. Homonymous facilitation was demonstrated to virtually all of the sampled motor units of biceps (BI), semitendinosus (ST), vastus lateralis (VL) and vastus medialis (VM). Heteronymous facilitation was readily demonstrated between VM and VL but was never obtained from ST to BI and never unequivocally obtained from BI to ST. Reciprocal inhibition was demonstrated from femoral nerve afferents to all of the sampled units of BI, and ST but reciprocal inhibition of VM or VL was never obtained from BI afferents and infrequently from ST afferents. These projections of group I afferents in man show certain specific differences from those of the cat and baboon that may reflect the normal function of the limb.

Key words

Ia EPSP Reciprocal inhibition Spinal reflexes Man 


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  1. Ashby P, Wiens M (1989) Reciprocal inhibition following lesions of the spinal cord in man. J Physiol (Lond) (in press)Google Scholar
  2. Ashby P, Zilm D (1982a) Relationship between EPSP shape and cross-correlation profile explored by computer simulation for studies on human motoneurons. Exp Brain Res 47: 33–40Google Scholar
  3. Ashby P, Zilm D (1982b) Characteristics of postsynaptic potentials produced in single human motoneurons by homonymous group I volleys. Exp Brain Res 47: 41–48Google Scholar
  4. Botterman BR, Hamm TM, Reinking RM, Stuart DG (1983a) Localization of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat biceps femoris muscle. J Physiol (Lond) 338: 335–377Google Scholar
  5. Botterman BR, Hamm TM, Reinking RM, Stuart DG (1983b) Distribution of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat semitendinosus muscle. J Physiol (Lond) 338: 379–393Google Scholar
  6. Brouwer B, Ashby P, Midroni G (1989) Excitability of corticospinal neurons during tonic muscle contractions in man. Exp Brain Res (in press)Google Scholar
  7. Cope TC, Fetz EE, Matsumura M (1987) Cross-correlation assessment of synaptic strength of single Ia fibre connections with triceps surae motoneurons in cat. J Physiol (Lond) 390: 161–188Google Scholar
  8. Crone C, Hultborn H, Jespersen B, Nielsen J (1987) Reciprocal Ia inhibition between ankle flexors and extensors in man. J Physiol (Lond) 389: 163–185Google Scholar
  9. Eccles JC, Eccles RM, Lundberg A (1957) The convergence of monosynaptic excitatory afferents on to many different species of alpha motoneurones. J Physiol (Lond) 137: 22–50Google Scholar
  10. Eccles JC, Eccles RM, Shealy CN (1962) An investigation into the effect of degenerating primary afferent fibers on the monosynaptic innervation of motoneurons. J Neurophysiol 25: 544–558Google Scholar
  11. Eccles RM, Lundberg A (1958) Integrative pattern of 1a synaptic actions on motoneurones of hip and knee muscles. J Physiol (Lond) 144: 271–298Google Scholar
  12. Fetz EE, Gustafsson B (1983) Relation between shapes of postsynaptic potentials and changes in firing probability of cat motoneurones. J Physiol (Lond) 341: 387–410Google Scholar
  13. Hongo T, Lundberg A, Phillips CG, Thompson RF (1984) The pattern of monosynaptic Ia connections to hindlimb motor nuclei in the baboon: a comparison with the cat. Proc R Soc Lond B 221: 261–289Google Scholar
  14. Kudina LP (1980) Reflex effects of muscle afferents on antagonist studied on single firing motor units in man. Electroencephalogr Clin Neurophysiol 50: 214–221Google Scholar
  15. Lloyd DPC (1946a) Facilitation and inhibition of spinal motoneurones. J Neurophysiol 9: 421–438Google Scholar
  16. Lloyd DPC (1946b) Integrative pattern of excitation and inhibition in two-neuron reflex arcs. J Neurophysiol 9: 439–444Google Scholar
  17. Mao CC, Ashby P, Wang M, McCrea D (1984) Synaptic connections from large muscle afferents to the motoneurons of various leg muscles in man. Exp Brain Res 56: 341–350PubMedGoogle Scholar
  18. Midroni G, Ashby P (1989) How synaptic noise may affect cross-correlations. J Neurosci Meth (in press)Google Scholar
  19. Mizuno Y, Tanaka R, Yanagisawa N (1971) Reciprocal group I inhibition of triceps surae motoneurons in man. J Neurophysiol 34: 1010–1017Google Scholar
  20. Nelson SG, Mendell LM (1978) Projection of single knee flexor Ia fibers to homonymous and heteronymous motoneurons. J Neurophysiol 41: 778–787Google Scholar
  21. Nelson SGT, Collatos TC, Niechaj A, Mendell LM (1979) Immediate increase in Ia-motoneuron synaptic transmission caudal to spinal cord transection. J Neurophysiol 42: 655–664Google Scholar
  22. Pierrot-Deseilligny E, Morin C, Bergego C, Tankov N (1981) Pattern of group I fibre projections from ankle flexor and extensor muscles in man. Exp Brain Res 42: 337–350Google Scholar

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • A. Bayoumi
    • 1
  • P. Ashby
    • 1
  1. 1.Playfair Neuroscience UnitUniversity of Toronto, Toronto Western HospitalTorontoCanada

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