Mechanical Aspects of Ciliary Propulsion

Cilia and eukaryotic flagella are motile cellular organelles, usually between 5/μm and 200 μm long and 0.2 μm in diameter, used to produce relative motion between a cell and its liquid environment. Cilia tend to occur in large numbers (hundreds) on the surfaces of cells, such as Tetrahymena or epithelial cells in the human lung. In contrast, flagellated cells bear small numbers of the organelles, usually one (Crithidia and many spermatozoa) or two (Chlamydomonas), but sometimes four (Trichomonas), eight (Hexamita) or larger numbers (the Hypermastigida). Cilia and eukaryotic flagella have the same basic structure and motile behaviour, so that to avoid repetition, and possible confusion with the prokaryotic flagellum, which has a different structure and mode of action from its eukaryotic counterpart, in this Chapter the eukaryotic organelles will be referred to collectively as cilia.