Motile cilia

Receptors are located on non-motile cilia that project from the dendrite of the neurone into the mucus layer. It is the cilia that possess the receptor for the pheromone and respond to it via an effector system that results in opening of a Na" ion channel. This depolarises the membrane across the sensory cell which, if of sufficient magnitude, leads to generation of action potential along the axon with which it forms a synapse. The effector system is adenyl cyclase and the generation of cyclic AMP, a process that involves the G-protein (Figure 12.15). 

Rohlich, P (1975) The sensory cilium of retinal rods is analogous to the transitional zone of motile cilia. Cell Tissue Res. 161, 421 30. 

Characters are used that may contain more noise than phylogenetic signal (characters of low probability of homology) and are not weighted to express their value. For example, reduction of epidermal microvilli, reductions of motile cilia and reductions of endodermal cilia are considered to be synapomorphies of the Ecdysozoa (Zrzavy et al., 1998). Simple reductions of this type are not very specific characters and occur frequently in unrelated organisms. 

The eukaryotic DNA is organized in to one or more linear molecules, called chromosomes, which are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria also contain some DNA. Many eukaryotic cells are ciliated with primary cilia. Eukaryotes can move using motile cilia or flagella. 

In general, cilia are widespread finger-like cell appendages. The structure of a proto-typic motile cilium is characterized as follows the ciliary shaft originates from a basal body complex in the apical cytoplasm beneath the plasma membrane (Figure 2A). 

Horst, C.J., Johnson, L.V. and Besharse, J.C. (1990) Transmembrane assemblage of the photoreceptor connecting cilium and motile cilium transition zone contain a coimnon immunologic epitope. Cell Motif Cytoskeleton 7 7, 329—344. 

The ability of the microtubules to slide past each other, propelled by the ATP-dependent mechano-chemical cycling of the dynein arms, brings about ciliary motility. Since the microtubules are constrained at the ciliary tip, it is possible to imagine how the sliding of microtubules on one side of the cilium might cause the cilium to bend. How such sliding is translated into a full beat cycle is still the subject of extensive research. 

Wolfmm, U. and Schmitt, A. (2000) Rhodopsin transport in the membrane of the connecting cilium of mammalian photoreceptor cells. Cell Motil. Cytoskeleton 46, 95-107. 

Satir, P. 1968. Studies on cilia. III. Further studies on the cilium tip and a sliding filament model of ciliary motility. J. Cell Biol., 39 77-94. 

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