Ciliary motion can be explained through the microtubule sliding theory involving axonemal dyneins. When axonemal dyneins are activated, they attempt to move along neighboring microtubule doublets, forcing them to slide relative to one another. As the doublets are cross-linked to one another by nexins and to the central microtubules by spokes, this crosslinking limits the extent of microtubule sliding by axonemal dyneins. Microtubule sliding is active only on a single side due to the switch inhibition mechanism, which ensures that dynein is active on one side and inactive on the other. This results in the bending of cilia in one direction. Switch inhibition also regulates the cycling between active and inactive phases of axonemal dynein and is responsible for alternate bending of the cilium. This results in a characteristic whip-like movement that is responsible for cell motility.