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Main Segment (main + segment)
Selected AbstractsMorphology and ultrastructure of the malpighian tubules of the Chilean common tarantula (Araneae: Theraphosidae)JOURNAL OF MORPHOLOGY, Issue 1 2002S. Renee Hazelton Abstract Relatively little is known about the morphology and ultrastructure of the Malpighian tubules of spiders (Arachnida: Araneae). Our study represents the first investigation of the Malpighian tubules of a theraphosid spider and is the only study to examine the living Malpighian tubules using confocal laser scanning microscopy. In theraphosid spiders, the Malpighian tubules originate from the stercoral pocket in the posterior portion of the opisthosoma and extend forward toward the prosoma in a dendritic pattern. There are three distinct segments (initial, main, and terminal), all dark brown in appearance. Each segment has distinctive ultrastructural features. Both the terminal and the main segment appear to be composed of at least two cell types with finger-like cytoplasmic protrusions associated with one of these types. The terminal segment, which is most proximal to the stercoral pocket, is the largest in diameter. It is composed of large, cuboidal cells containing many mitochondria and lipid inclusions. The main segment is intermediate in diameter with many mitochondria and secretory vesicles present. The initial segment is relatively thin in comparison to the other segments and is intimately associated with the digestive gland. The cells of the initial segment contain very little cytoplasm, fewer mitochondria, secretory vesicles, and prominent inclusions. J. Morphol. 251:73,82, 2002. © 2002 Wiley-Liss, Inc. [source] Quantitative analyses of anatomical and electrotonic structures of local spiking interneurons by three-dimensional morphometry in crayfishTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 3 2001Ryou Hikosaka Abstract We quantitatively investigated the three-dimensional structure of the dendrites of local spiking interneurons using a confocal laser scanning microscope in the terminal abdominal ganglion of crayfish. We also studied their passive membrane properties electrophysiologically using the single-electrode current clamp techniques to analyze their electrotonic structure. All of the local spiking interneurons examined in this study lacked distinctive axonal structure and had a monopolar cell body that was connected with a fine primary process to a thick main segment. Numerous fine secondary processes projected from the main segment in the ganglionic neuropile. The average anatomical length of a secondary process from the main segment to its terminal was 261.9 ± 15.2 ,m. The average input resistance and membrane time constant of local spiking interneurons, obtained from their voltage responses to intracellular injection of step current pulses in the main segment, were 15.2 ± 1.6 M, and 13.9 ± 1.9 msec, respectively. Calculation of the electrotonic length of dendritic processes based on morphological and physiological data obtained in this study revealed that the average electrotonic length of secondary processes in local spiking interneurons was significantly longer than in local nonspiking interneurons, although both types of local interneurons showed apparently similar anaxonic structure. The steady-state voltage attenuation factors for the secondary processes of local spiking interneurons were significantly greater than those of local nonspiking interneurons in both centrifugal and centripetal directions. The larger electrotonic structure of local spiking interneurons compared to that of nonspiking interneurons appears to be compensated for by their excitable dendritic membrane. J. Comp. Neurol. 432:269,284, 2001. © 2001 Wiley-Liss, Inc. [source] Clustering of Chinese tourists to Singapore: an analysis of their motivations, values and satisfactionINTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 4-5 2005Ah Keng Kau Abstract This paper presents the findings of a survey through the use of a structured questionnaire of over 240 visitors from China to Singapore in February 2003. The main objective is to determine if these tourists could be effectively segmented based on their motivations for travel. The analysis of the survey data confirmed that they could be clustered into four main segments. Each of the segments was found to possess unique profiles in terms of demographic background, trip-related characteristics and personal values. The segments were also assessed of their levels of satisfaction with various attributes offered by Singapore as a tourist destination. In addition, their overall satisfaction, likelihood of revisit and likelihood of making positive word-of-mouth recommendation to others were also determined. In all of these, the segments were found to differ significantly from each other. Finally, the implications of these findings were discussed and suggestions made as to how Singapore could effectively develop marketing strategies to attract these tourists, bearing in mind that China was the third largest tourist generating country for Singapore and they collectively contributed over S$300 million to the Singapore economy in 2002. In fact, tourist arrival from China increased further after SARS in 2003, reaching over 880,000 in 2004 and became the second largest tourist group after Indonesia. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||