The Importance of the Cortico-Motoneuronal System for Control of Grasp

  1. Gregory R. Bock organizer and
  2. Jamie A. Goode
  1. R. N. Lemon,
  2. S. N. Baker,
  3. J. A. Davis,
  4. P. A. Kirkwood,
  5. M. A. Maier and
  6. H.-S. Yang

Published Online: 28 SEP 2007

DOI: 10.1002/9780470515563.ch11

Novartis Foundation Symposium 218 - Sensory Guidance of Movement

Novartis Foundation Symposium 218 - Sensory Guidance of Movement

How to Cite

Lemon, R. N., Baker, S. N., Davis, J. A., Kirkwood, P. A., Maier, M. A. and Yang, H.-S. (2007) The Importance of the Cortico-Motoneuronal System for Control of Grasp, in Novartis Foundation Symposium 218 - Sensory Guidance of Movement (eds G. R. Bock and J. A. Goode), John Wiley & Sons, Ltd., Chichester, UK. doi: 10.1002/9780470515563.ch11

Author Information

  1. Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, London WC1N 3BG, UK

Publication History

  1. Published Online: 28 SEP 2007

ISBN Information

Print ISBN: 9780471982623

Online ISBN: 9780470515563

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Keywords:

  • cortico-motoneuronal system;
  • supplementary motor area;
  • monosynaptic excitation;
  • cortical control;
  • CM projections

Summary

Our recent work has revealed new evidence of the importance of direct cortico-motoneuronal (CM) connections for voluntary control of the hand. Most of these connections are derived from corticospinal neurons located in the M1 hand area, although there are some much smaller contributions from other secondary motor areas, such as the supplementary motor area (SMA). Intracellular recordings show that 75% of upper limb motoneurons in the chloralose-anaesthetized macaque monkey receive a monosynaptic projection from the corticospinal tract; evidence for non-monosynaptic, propriospinal excitatory influences from the corticospinal tract was conspicuously lacking in these anaesthetized preparations. Moreover, in the conscious monkey, hand and arm muscle motor unit responses to corticospinal tract input are dominated by single, brief peaks compatible with monosynaptic excitation. CM excitatory post- synaptic potentials, recorded from a comparable sample of hand and arm motoneurons in anaesthetized macaque and squirrel monkeys, were found to be larger and faster rising in the macaque, which is by far the more dextrous of the two species. CM cells facilitating a given muscle in the conscious macaque are distributed over a wide region of M1 cortex, and each contributes a particular pattern of discharge during a skilled task. In addition to their direct effects on target muscles there may be weaker but potentially important effects that derive from the synchronous binding of assemblies of output neurons. Synchronous oscillations between these neurons are particularly prevalent during steady grip, but disappear during digit movement.