Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgements
- List of abbreviations
- 1 General methodology
- 2 Monosynaptic Ia excitation and post-activation depression
- 3 Muscle spindles and fusimotor drive: microneurography and other techniques
- 4 Recurrent inhibition
- 5 Reciprocal Ia inhibition
- 6 Ib pathways
- 7 Group II pathways
- 8 Presynaptic inhibition of Ia terminals
- 9 Cutaneomuscular, withdrawal and flexor reflex afferent responses
- 10 Propriospinal relay for descending motor commands
- 11 Involvement of spinal pathways in different motor tasks
- 12 The pathophysiology of spasticity and parkinsonian rigidity
- Index
- References
5 - Reciprocal Ia inhibition
Published online by Cambridge University Press: 08 August 2009
- Frontmatter
- Contents
- Preface
- Acknowledgements
- List of abbreviations
- 1 General methodology
- 2 Monosynaptic Ia excitation and post-activation depression
- 3 Muscle spindles and fusimotor drive: microneurography and other techniques
- 4 Recurrent inhibition
- 5 Reciprocal Ia inhibition
- 6 Ib pathways
- 7 Group II pathways
- 8 Presynaptic inhibition of Ia terminals
- 9 Cutaneomuscular, withdrawal and flexor reflex afferent responses
- 10 Propriospinal relay for descending motor commands
- 11 Involvement of spinal pathways in different motor tasks
- 12 The pathophysiology of spasticity and parkinsonian rigidity
- Index
- References
Summary
The disynaptic pathway mediating reciprocal Ia inhibition to antagonistic motoneurones through Ia interneurones has been investigated extensively in animal experiments, and is the most thoroughly studied spinal circuit in human subjects. The extensive convergence described on Ia interneurones provided the first example of integration in the spinal cord. It has been suggested that motoneurones and Ia interneurones are controlled in parallel from the brain to produce a co-ordinated contraction of agonists and relaxation of antagonists (Lundberg, 1970). This appealing hypothesis prompted experiments in humans, and the study of changes in reciprocal Ia inhibition from ankle flexors to extensors during voluntary dorsiflexion was the first attempt to investigate changes in transmission in spinal pathways during movement (Tanaka, 1974). Although the results recorded during tonic contractions have long been a matter of dispute, the existence of a parallel control of α motoneurones and corresponding Ia interneurones has now been demonstrated in a number of motor tasks at ankle level. However, it has proved difficult to extrapolate from results obtained at ankle level to wrist flexors and extensors. It has become clear that reciprocal inhibition between flexors and extensors in the forearm is probably mediated by non-reciprocal group I interneurones (so-called Ib inhibitory interneurones), and not by ‘true’ Ia inhibitory interneurones.
Background from animal experiments
Initial findings
In a decerebrate preparation Sherrington (1897) demonstrated that the contraction of a muscle is accompanied by relaxation of its antagonist(s), and coined the term ‘reciprocal inhibition’.
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- Information
- The Circuitry of the Human Spinal CordIts Role in Motor Control and Movement Disorders, pp. 197 - 243Publisher: Cambridge University PressPrint publication year: 2005