Cilia - The Little moving Hair

Just as some cells can move like an amoeba and get where they want to, with the help of pseudopodia, some others can use tiny hair like parts, called cilia. The word 'cilia' is the plural of cilium, which really means - short curved hairs that grow from the edges of the eyelids - that is eyelashes.

Cilia are microscopic hairlike processes extending from the free surface of a cell. They are capable of beating in an organized, rhythmic fashion.

Where do you find the cilia? Oh, they are in human body in parts like - trachea or the windpipe, in the central canal of spinal cord, fallopian tube or the oviduct in female reproductive system, in the ventricles of the brain. They are seen in olfactory receptors in nose and in organ of Corti in internal ear.

Please take a look at the - animated movement of cilia in the organ of corti http://www.sissa.it/bp/Cochlea/cortifm.h...

and at stationary cilia at - http://www9.biostr.washington.edu/cgi-bi...

The cilia can also be seen in a whole class of tiny protozoa, called ciliates - such as Paramecium, opalina, Balantidium, also in vorticella, in earthworm's excretory organs called nephridia, in the gills of snails and fish, and in aquatic fungi, algal reproductive cells. See the protzoon cilia beating -

http://www.microscopy-uk.org.uk/mag/artj...

Please take a look at simplified diagram of cilia in a transverse section as would be seen under an electron microscope. They are shown about 300,000 times bigger than they really are.

A cilium has two main parts - the basal body, usually beneath cell surface, and the shaft - a bundle of pairs of fibrils. The basal body has 9 triplets of fibrils at the rim. The shaft is 5-10 micrometers long and has - 9 pairs of fibrils at the rim and one pair in the center. This arrangement is shown as 9 (2) + 2.i.e. nine doublets at periphery and 2 fibrils at the center. The bundle of fibrils in shaft is known as axoneme and a membrane continuous with the cell membrane covers it. The fibrils are made of a protein, called tubulin.

Out of the pair of fibrils, one appears as a complete circle in a cross section is tubule A and has two arms made of a protein, dynein. The fibril appearing, as an incomplete circle in cross section is the fibril B. It shares three filaments of A fibril. The B fibril does not have any dynein arms.

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