Ultrastructural depiction of the base of a generic mammalian cilium. The basal body (BB), derived from the mother centriole, nucleates the microtubule axoneme of the cilium. The basal body ends at the terminal plate (tp) and the transition fibers. The transition fibers are electron dense fibers at the base of the cilium connecting the ciliary axoneme to the plasma membrane. The transition zone (TZ) is characterized by the presence of the ciliary necklace on the ciliary membrane (not depicted) and Y-linkers, the end of which correspond with the basal plate (bp). In cilia that contain central microtubules, these emanate from the basal plate. The transition fibers and transition zone encompass the so-called 'ciliary gate', which possibly regulates protein entrance and exit. The fibers act as docking sites for intraflagellar transport particles and their motors, and could form part of a pore complex similar to the nuclear pores. The daughter centriole, connected to the basal body via an interconnecting fiber, and striated rootlet are also depicted. The ciliary pocket is an invagination of specialized cell membrane at the base of the cilium likely to be important for regulation of cilia composition.