Multicyclic scratch reflex movements in the terrapinpseudemys scripta elegans
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We present observations on the multicyclic scratch reflex in spinal terrapins as produced by a brief mechanical stimulus to specific regions of the shell. Hip and knee movements and EMG's from several muscles are simultaneously recorded.
We confirm the results of Stein and Grossman (1980) that the EMG's during a movement cycle can be divided into three phases. We have related this three-phase structure to the movement pattern.
Variations in duration and intensity of the EMG patterns are seen when the cycles of a multicyclic response are compared with each other, but the phasic sequence of firing and the grouping of muscle activities is not changed.
Disturbances in the EMG pattern can be seen if the movement is obstructed but the three-phase structure is maintained. If the movement is prevented by holding the limb, a different combination of muscles may be simultaneously active which does not comply with the three-phase division.
Our observations are compatible with the view that the scratch reflex is centrally programmed but the program can be modified by afferent inputs and by an undefined influence from within the spinal cord. We are not able to reconcile our results with the concept of a half-centre model system for the reflex control.
KeywordsSpinal Cord Stein Muscle Activity Specific Region Movement Pattern
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