Almost every neuron has a single primary cilium extending from its cell body. Like primary cilia in other vertebrate cell types, these organelles are nonmotile and have a backbone of 9 microtubule doublets. Most neuroscientists are not yet aware that neurons have cilia, and little is known about their function. It is now known that primary cilia are necessary for our very existence. Without primary cilia in the embryonic node, vertebrates die early in development. Individual organs such as the kidney are severely defective if their primary cilia are missing.