Figure 1. Overview of ciliary ultrastructure and comparison between motile and non-motile cilia.

A. Scanning electron micrograph of mouse nodal cilia (image reproduced with permission from Shigenori Nonaka). B. Motile cilia are usually found at a density of several hundred per cell, as shown in this scanning electron micrograph of the mammalian trachea (image from [102]). C. Primary cilia are typically one per cell, as exemplified by primary cilia in renal tubule epithelia (image from [102]). D. Schematic representation of a cilium, with cross sections at the distal end showing the microtubule arrangements in the nodal, motile and non-motile (primary) cilia, and the basal body at the apical side of the cell. DRC, dynein regulatory complex.