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On the Functional Significance of Long Monosynaptic Descending Pathways to Spinal Motoneurones

  • P. A. Kirkwood
  • J. D. Road

Abstract

Studies in behaving animals show that the activities of neurones with direct long descending connections to motoneurones, such as corticomotoneuronal cells to hand muscles in the primate, often do not co-vary with the activities of the target muscles. Explanations for this include the operation of populations of neurones involving many input cells with different patterns affecting many motoneurones of different muscles, estimated via network analysis (Fetz, 1992), or the effects of other pathways setting recruitment patterns at motoneuronal level (Bennett & Lemon, 1994). The pathways that include these long monosynaptic connections are accorded a great deal of importance in controlling the movements concerned and it seems to be most often assumed that it is the excitation derived via this direct link that is the most important part of the control. In contrast we present here results from another system which shows an extreme case of lack of co-variance, and we argue from these that rather more importance should be given to events at spinal level in producing the patterns of motoneurone output.

Keywords

Target Muscle Spinal Interneurones Monosynaptic Connection Ventral Respiratory Group Expiratory Neuron 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Bennett, K. M. B. & Lemon, R. N. (1994) The influence of single monkey cortico-motoneuronal cells at different levels of activity in target muscles. J. Physiol. 477, 291–307.PubMedGoogle Scholar
  2. Davies, J. G. McF., Kirkwood, P. A. & Sears, T. A. (1985a) The detection of monosynaptic connexions from inspiratory bulbospinal neurones to inspiratory motoneurones in the cat. J. Physiol. 368, 33–62.PubMedGoogle Scholar
  3. Davies, J. G. Mcf., Kirkwood, P. A. & Sears, T. A. (1985b) The distribution of monosynaptic connexions from inspiratory bulbospinal neurones to inspiratory motoneurones in the cat. J. Physiol. 368, 63–87.PubMedGoogle Scholar
  4. Fetz, E. E. (1992) Are movement parameters recognizably coded in the activity of single neurons? Behav. Brain Sci. 15, 679–690.Google Scholar
  5. Kirkwood, P. A. (1995) Synaptic excitation in the thoracic spinal cord from expiratory bulbospinal neurones in the cat. J. Physiol. 484, 201–225.PubMedGoogle Scholar
  6. Kirkwood, P. A., Schmid, K. & Sears, T. A. (1993) Functional identities of thoracic respiratory interneurones in the cat. J. Physiol. 461, 667–687.PubMedGoogle Scholar
  7. Merrill, E. G. & Lipski, J. (1987) Inputs to intercostal motoneurons from ventrolateral medullary respiratory neurons in the cat. J. Neurophysiol. 57, 1837–1853.PubMedGoogle Scholar
  8. Lundberg, A. (1992) To what extent are brain commands for movements mediated by spinal interneurones? Behav. Brain Sci. 15, 775–776.Google Scholar
  9. Miller, A. D., Tan, L. K. & Suzuki, I. (1987) Control of abdominal and expiratory intercostal muscle activity during vomiting: role of ventral respiratory group expiratory neurons. J. Neurophysiol. 57, 1854–1866.PubMedGoogle Scholar
  10. Sears, T. A. (1964). The slow potentials of thoracic respiratory motoneurones and their relation to breathing. J. Physiol. 175, 404–424.PubMedGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1995

Authors and Affiliations

  • P. A. Kirkwood
    • 1
  • J. D. Road
    • 2
  1. 1.Sobell Department of NeurophysiologyInstitute of NeurologyLondonUK
  2. 2.Department of MedicineUniversity of British ColumbiaVancouverCanada

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