Ultrastructure of Invertebrate Chemo-, Thermo-, and Hygroreceptors and Its Functional Significance

Publisher Summary Chemo-, thermo-, and hygroreceptors are primary sensory cells, which bear one or several modified cilia whose membranes are specialized to take part in the transduction process. These membranes must be exposed to the stimuli but also be protected against desiccation, mechanical, and other injury. Hence, a variety of structural specializations is found that serves these functions. In insects, chemo-, thermo-, and hygroreceptive sensory cells are located exclusively in sensilla, which are organelles built up by a definite number of characteristic cells. During development, the innermost enveloping cell produces a cuticular sheath (scolopale), which envelops the dendritic processes for varying distances along their course through the receptor lymph cavity. This sheath producing cell is surrounded by the trichogen cell, which is itself surrounded by the trichogen cell. These cells build up shaft and socket, respectively, of the cuticular outer structures during development. The perikarya of all cells of the sensillum are enclosed within the epidermis.