Electron microscopy of normal ciliary ultrastructure in cross-section

Electron micrographs showing normal ciliary ultrastructure in cross section at (A) the core of the ciliary axoneme with a 9+2 microtubular arrangement; (B) the tip of the cilium with single microtubules (thick arrow); and (C) the base of the axoneme showing absent central pair. Panel (D) gives a diagrammatic representation of normal ciliary ultrastructure in cross sections at the tip, central axoneme, and base. The narrow arrows depict the ODAs and the dashed arrows depict the IDAs. The thick arrow indicates the tip of the cilium with single microtubules (these are a normal part of ciliary ultrastructure and should not be assessed for diagnosis of Class 1 or Class 2 defects). The arrowhead indicates where there is no central pair. Microtubular doublets are often linked to the ciliary membrane with Y-shaped linker, best seen in panel C.