Terminology
The cilia oscillate repeatedly at the frequency of several times per second or even dozens of times. In addition, when responding to stimulation, the direction of cilia movement can be changed, or the movement can be stopped suddenly. Since the Reynolds number is less than 10-2, the hydrodynamic effect of motion depends on the viscosity of the external fluid rather than the inertia. The ciliated epithelium produces gliding water flow or propulsive force through the coordination of most cilia. Ciliary movement plays a role in swimming of ciliates, filtering feeding of axopods, primitive chords, etc., body fluid circulation of sea urchins, etc., transfer of excreta and reproductive products of renal tubes, renal tubules, reproductive ducts, etc., and cleaning of respiratory tract. Compared with muscle contraction, there is no obvious deformation effect of somatic cells and tissues. Ciliary movement is affected by temperature and pH, and there are also examples of innervation. ATP is a direct energy source. Some claim that the power of motion is from the local sliding of surrounding microtubules, while others believe that motion is based on contraction.
