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Medical Definition of Radial spoke
1. The structure that links the outer microtubule doublet of the ciliary axoneme with the sheath that surrounds the central pair of microtubules. The spokes are arranged periodically along the axoneme every 29nm, have a stalk about 32nm long and a bulbous region adjacent to the sheath. at least 17 different polypeptides are associated with the spokes. Spokes are thought to restrict the sliding of doublets relative to one another, digestion of the radial spokes will allow sliding apart of the doublets. This entry appears with permission from the Dictionary of Cell and Molecular Biology (11 Mar 2008)