. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. B +20 - + 10 - (f> 0 • 1 I 1 !*• * 1 1 1 ^* 1 1 1 1 r* T 1 1 1 CD en • •• 9 . • 100 CO .• • • * Stimulation phase (%) 0. -10 • tion in the heart, the same effects on the muscle activity were induced. Discussion Branchiopod hearts kick u curdinc ganglion The heart of Triops longicaudatus consists of a single layer of myocardial cells. Myotibrils are found in the outer half of these cells (Fig. 1C). Electron microscopic observations on the heart of another tadpole shrimp, Lepi- dithis arcticus, showed that the heart consist
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. B +20 - + 10 - (f> 0 • 1 I 1 !*• * 1 1 1 ^* 1 1 1 1 r* T 1 1 1 CD en • •• 9 . • 100 CO .• • • * Stimulation phase (%) 0. -10 • tion in the heart, the same effects on the muscle activity were induced. Discussion Branchiopod hearts kick u curdinc ganglion The heart of Triops longicaudatus consists of a single layer of myocardial cells. Myotibrils are found in the outer half of these cells (Fig. 1C). Electron microscopic observations on the heart of another tadpole shrimp, Lepi- dithis arcticus, showed that the heart consists of a single layer of strongly polarized myocardial cells, each with their myofibrillar part facing the epicardium (Tj0nneland, er til., 1980). The myofibrils cross each other in the cell and form a contractile network. Tj0nneland et al. also found intercalated discs between adjacent myocardial cells in the region of the myofibrils. No nerve cells were found in the heart of Triops by -20 - -30 L Figure 7. Effects on the muscle activity of injecting a brief hyperpo- larizing current pulse. (A) Each record shows the intracellular activity of the heart muscle (upper trace) and a stimulus monitor (lower trace). The recording electrode was inserted near the anterior end of the heart, and the current electrode near the posterior end. A brief hyperpolarizing current pulse (50 ms, 50 nA) was applied at various phases (stimulation phase) of the inter-peak interval. See text for definitions of the stimula- tion phase and the inter-peak interval. Stimulation phases were 369f (1) and 85c/r (2). (B) Relationship between phase shift and stimulation phase (phase-response curve). Fifty brief hyperpolarizing pulses were applied at various stimulation phases. Each phase delay (+) or phase advance ( —) was plotted against each stimulation phase. From the same prepara- tion as in Fig. 6. applied current increased (E, 50 nA). Hyperpolarizing DC current of high intensity (F. 6
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
