Cilium is made up of microtubules coated in the plasma membrane. The microtubules are like small hollow rods that are made up of the protein tubulin. Each cilium contains nine pairs of microtubules that form the outside of a ring and also the two central microtubules. This structure is called an axoneme, and the arrangement is called ‘9+2’, an arrangement ubiquitous in motile cilia. The microtubules are held together through the cross-linking proteins. There are nine outer pairs between motor proteins called dynein.Cilia attach to the cell at a basal body which is made up of microtubules arranged as nine triplets. The triplets are formed just like the doublets from the cilia. They are always joined by an additional microtubule from the cell. The two central microtubules will end before taking an entry to the basal body.The motor proteins that are dynein are large flexible molecules that allow the cilia to be motile. The protein always hydrolyzes ATP for energy. When proteins are activated, they undergo conformational changes which in turn allow for complex movements. The dynein molecules essentially crawl along the microtubules, and pull the neighbouring doublet up, and also reattach further down. Because the doublets are attached by the cross-linking proteins, they can only slide a short distance from each other. This movement causes bending in the cilium.Cilia are very tiny structures that measure approximately 0.25 μm in diameter and up to 20 μm in length. They are found in huge numbers on the surface of the cell. The cilia always act like the oars, beating back and forth to create movement.