Summary
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1.
Contraction burst pulses are blocked more frequently by horizontal bridges than by vertical tissue bridges of the same width. S-shaped mazes blocked pulses more frequently than E-shaped mazes of the same width.
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2.
The conducting path for the contraction burst pulse was thought to be a longitudinally continuous pathway having discontinuous, randomly distributed horizontal transmission sites.
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3.
‘Contraction burst’ pulses in isolated head preparations arise at distinct hypostomal loci immediately adjacent to the last tentacle of a sequence to contract.
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4.
Such a ‘contraction burst’ locus might be another hypostomal tentacle pulse initiation site whose activity had been facilitated to spread over the entire hypostome.
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5.
Cluster and crescendo firing of tentacles in more elliptically shaped heads are thought to represent incomplete ‘contraction bursts’ which can facilitate the occurrence of the ‘contraction burst’ itself.
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6.
Contraction burst pulses originating on one side of split-body preparations were conducted only down that side without being transmitted across the hypostome.
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7.
It is suggested that the longitudinal conducting paths are represented by the longitudinally running myofilaments of the epithelial cell muscle processes. Horizontal and vertical transmission sites between cells are represented by desmosomes and tight junctions. Pulse initiation is thought to occur at neuromuscular junctions on the conducting tracts of the column.
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This work was supported by NSF grant No. B012421. I would like to thank L. M. Passano, in whose laboratory this work was done, for his support and encouragement and for critically reading the manuscript. I would also like to thank Hans Zoerb for his technical assistance, Cheryl Hughes for preparing the text figures and Linda Knox for typing the manuscript.
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Kass-Simon, G. Longitudinal conduction of contraction burst pulses from hypostomal excitation loci inHydra attenuata . J. Comp. Physiol. 80, 29–49 (1972). https://doi.org/10.1007/BF00694326
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DOI: https://doi.org/10.1007/BF00694326