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Presynaptic and postsynaptic mechanisms underlying H-reflex changes produced by a selective voluntary contraction
M Abbruzzese1, L Reni, C Minatel
1Department of Neurological Sciences, University of Genoa, Italy.
Muscle & Nerve
|April 9, 1998
Summary
During voluntary muscle contraction, the soleus H reflex enhances, and central delay shortens. However, during release, la afferent effectiveness decreases, impacting motoneuronal responsiveness.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- The soleus H reflex is a valuable tool for assessing spinal cord excitability.
- Understanding neural adaptations during voluntary muscle contraction and release is crucial for motor control research.
Purpose of the Study:
- To investigate changes in the soleus H reflex, central motor pathway delay, and la afferent effectiveness during isometric voluntary contraction and subsequent release.
- To differentiate the effects of contraction and release on motoneuronal responsiveness.
Main Methods:
- Concurrent recording of soleus H reflex, afferent (P1), and efferent (P2) volleys during sustained isometric soleus muscle contraction and release.
- Utilizing control experiments including neural blockade, muscle stretching, and modulation of homonymous/heteronymous responses.
Main Results:
- Voluntary contraction enhanced the H reflex and significantly reduced the central delay (P1-P2 interval).
- The release phase showed the opposite trend for central delay and reduced la afferent effectiveness.
- Postsynaptic motoneuronal responsiveness was altered only during contraction, not release.
Conclusions:
- Voluntary contraction modulates spinal excitability by enhancing H reflex and shortening central delay.
- Both contraction and release phases involve reduced la afferent effectiveness, but only contraction impacts postsynaptic motoneuronal responsiveness directly.