Can Facilitation Increase The H-Reflex In Micro-G?
- Paper number
IAC-07-A1.I.07
- Author
Mr. Felix Betzler, Charite Universitaetsmedizin Berlin, Germany
- Year
2007
- Abstract
This study was undertaken to examine the “Hoffmann-reflex”. The Data were collected during two parabolic flights on September 13th and 14th 2006, in the course of the 9th Student Parabolic Flight Campaign. BACKGROUND: The Hoffmann-reflex (H-reflex) is the reflex response of a muscle after electrical stimulation of sensory so called Ia-fibres in its innervating nerve. These fibres enter the spinal cord and form activating synapses with alpha-motoneurons inducing the contraction of the muscle. Facilitation i.e. the Jendrassik-manoeuvre (JM) is a mechanism which facilitates and amplifies the reflex response. It is commonly used in clinical neurology to reinforce the reflex responsiveness, but the mechanism is not yet fully understood. OBJECTIVES: the aims of this study were: a) to ascertain that the micro-G environment alone has an impact on the muscle reflex response, and b) to find out whether facilitation performed during micro-G results in a further amplification of reflex response. METHODS: The Ia-fibres of the tibial nerve, belonging to the soleus muscle in the lower leg, were stimulated by low electric stimuli, seven of them during each phase of one parabola (hyper-gravity, micro-gravity, normo-gravity). The muscle response (H-wave) was measured by bipolar electrodes over the soleus muscle, and recorded as electromyogram. RESULTS: Valid data were collected from three subjects. The results are the following: there is a significant increase in the reflex-responsiveness in micro-g on two subjects, a decrease on one subject. Facilitation leads to a further amplification but the elevating effect in micro g is weaker than in ground conditions. Thus, reflex response in general can not be increased endlessly, and therefore the JM effect declines through micro-g (which itself already has an increasing influence on reflex response). Besides, an unexpected, not yet explainable phenomenon occurred in the normo-G phase of the flight: the reflex-response decreased while applying JM.
- Abstract document