![]() ![]() This conclusion stems from recent observations that the molecular machinery for taste transduction, including G-protein-coupled taste receptors (GPCRs) and downstream effectors, is primarily expressed in Type II cells. Type II cells are likely to be the primary sensory receptor cells in the taste bud. ![]() Gustatory signal processing and synapses in taste buds Presently, the field is in the awkward stage of transition from a historical nomenclature based on electron micrographs to molecular and functional profiles based on immunostaining, in situ hybridization and single cell reverse transcription-polymerase chain reaction (RT-PCR). These categories may be more revealing regarding taste bud function. The original categorization of taste cells based on cytological and ultrastructural features is being eclipsed by more recent classifications based on the expression of certain molecules. In contrast, Types II and III cells appear to represent taste receptor cells and synaptic output cells, respectively, for taste signaling (see below). Basal and Type I cells, although undoubtedly important players in the taste bud, will not be discussed further in this review because their roles in signal processing are presently unknown. Type I cells are believed to be supporting cells and may have glial-like properties such as those described by Bigiani. Basal (Type IV) cells are progenitor cells that restock the taste bud during its normal course of cell turnover. Historically, mammalian taste bud cells have been classified into four categories on the basis of their cytological and ultrastructural features: Type I, II, III, and basal or Type IV cells. These gustatory end organs transmit signals to afferent nerves by way of synapses between taste cells and primary afferent sensory fibers, and perhaps also from cell to cell within a taste bud. ![]() Taste buds are peripheral sensory organs that respond to a wide variety of sapid chemicals. ![]()
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