2 results
8 - Lesions of the periphery and spinal cord
-
- By Michael J. Angel, Toronto Western Hospital, Ontario, Canada, Nicholas J. Davey, Department of Sensorimotor Systems, Imperial College School of Medicine, Charing Cross Hospital, London, UK, Peter H. Ellaway, Department of Sensorimotor Systems, Imperial College School of Medicine, Charing Cross Hospital, London, UK, Robert Chen, Toronto Western Hospital, Ontario, Canada
- Edited by Simon Boniface, Ulf Ziemann, Johann Wolfgang Goethe-Universität Frankfurt
-
- Book:
- Plasticity in the Human Nervous System
- Published online:
- 12 August 2009
- Print publication:
- 15 May 2003, pp 204-230
-
- Chapter
- Export citation
-
Summary
Introduction
Functional recovery or compensation following nervous system injury may be facilitated by plasticity within the central nervous system. For example, activation of the visual cortex that occurs during Braille reading in the early blind (under 14 years of age) is of functional importance (Cohen et al., 1997) and there is convincing evidence that plasticity can play an adaptive role following deafferentation (Pascual-Leone & Torres, 1993). Whether this kind of functional reorganization occurs in the motor system is less clear.
In the motor system, the skilled use of our muscles requires the integrative actions of sensory feedback and descending motor commands, which result in appropriate activation of motoneurones through activation of spinal interneurons, i.e. sensorimotor integration (Baldissera et al., 1981).The corticospinal system, the vital component of volitional movement, controls spinal motoneuronal activity through interneuronally mediated pathways (Lundberg & Voorhoeve, 1962; Pierrot-Deseilligny, 1996; Alstermark et al., 1999), and through their direct monosynaptic contacts with spinal motoneurons (Jankowska et al., 1975). The alterations in the control of the corticospinal system have received the greatest attention in TMS studies of plasticity in humans.
The importance of tonic sensory input in regulating cortical excitability and cortical body part representation in the motor cortex was initially shown in animal studies wherein peripheral nerve injury triggers a massive reorganization in the rat (Sanes et al., 1990).
MOTOR UNIT DISCHARGE CHARACTERISTICS DURING VOLUNTARY CONTRACTION IN PATIENTS WITH INCOMPLETE SPINAL CORD INJURY
- HAZEL C. SMITH, NICK J. DAVEY, GORDANA SAVIC, DAVID W. MASKILL, PETER H. ELLAWAY, HANS L. FRANKEL
-
- Journal:
- Experimental Physiology / Volume 84 / Issue 6 / November 1999
- Published online by Cambridge University Press:
- 04 January 2001, pp. 1151-1160
- Print publication:
- November 1999
-
- Article
- Export citation
-
Synchronisation of motor unit discharges is commonly seen in hand muscles of normal man but is absent following neurologically complete spinal cord injury and reduced after stroke. These findings support the notion that some corticospinal inputs to motoneurones are shared and contribute to the observed synchrony of discharge. In this study we have examined motor unit discharge in hand muscles below the level of an incomplete spinal cord injury in an attempt to relate strength of synchrony to the integrity of the corticospinal tract. Eight patients with incomplete spinal cord injury (neurological level C3-C7) and eight control subjects took part in the study. The patients had sustained injury 14-191 weeks prior to the recordings and had since regained good motor function in their hands. Two concentric needle electrodes were inserted into the first dorsal interosseus muscle which subjects were instructed to contract weakly so that potentials from individual motor units could be reliably identified on both recordings. Synchrony was detected by constructing cross-correlograms between the discharges of pairs of individual motor units. The amount of synchronous firing was determined from the magnitude of any peak in the cross-correlogram, as the probability above chance (XP) of one motor unit firing with respect to the other and vice versa. The degree of synchrony was lower (P < 0·05) in the patient group (mean XP 0·06) than in the control group (mean XP 0·09). The incidence of significant synchrony was lower in the patient group (41·8 %) than in the control group (92·9 %). The mean (± S.E.M.) frequency of motor unit discharge was slightly lower (P < 0·05) in patients (9·7 ± 0·4 impulses s-1) than controls (10·8 ± 0·5 impulses s-1). The mean width of synchrony peaks was narrower (P < 0·05) in patients (11·4 ± 1·1 ms) than controls (13·2 ± 0·6 ms). We conclude that the weaker synchrony of motor unit discharge in incomplete spinal cord injury may reflect permanent damage to some corticospinal axons.