Interactions of spino-bulbo-spinal reflexes with cortically evoked pyramidal and extrapyramidal activities

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Abstract (1) Experiments were performed on 29 cats under chloralose anesthesia, with the purpose of investigating whether a relationship exists between the neuronal mechanism of the spino-bulbo-spinal (SBS) reflex and extrapyramidal mechanisms which induce long latency evoked spinal responses. (2) Single shocks to the motor cortex yielded early and late responses from the spinal cord in both the dorsal and the ventral roots and in the cord dorsum simultaneously. (3) The early response from the ventral root, dorsal root and cord dorsum was apparently mainly due to pyramidal mechanisms, since there was a marked alteration in these following section of the pyramids. (4) The late response noted above was not significantly modified by sectioning of the pyramids, although it was eliminated by spinal transection, leaving the pyramids intact. Asphyxia and Nembutal anesthesia affected the late responses more than the initial ones. These observations combine to suggest that the late responses are likely to be due to extrapyramidal mechanisms. (5) Blocking interactions between SBS reflex responses and cortically evoked extrapyramidal activities were observed. The site of this interaction was presumed to be in the brain stem. (6) Descending pathways of the SBS reflex were interpreted as being identical or similar to those involved in cortically evoked extrapyramidal responses.

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