Fig. 1
From: The annulus: composition, role and importance in sperm flagellum biogenesis and male fertility
Schematic representation of the spermatozoa with cross sections of the different segments. The flagellum is composed of a central structure called the axoneme, a structure composed of 9 peripheral microtubules doublets and a central pair. The flagellum is divided into two parts: the midpiece which contains the mitochondrial sheath and the dense fibers, surrounding the axoneme, and the principal piece which contains the fibrous sheath around the axoneme. These two main compartments are separated by the annulus. The terminal piece of the flagellum only contains the axoneme. Ax: axoneme, ODF: Outer Dense Fiber, M: Mitochondria, LC: Longitudinal columns, FS: Fibrous Sheath, MD: Microtubule doublet, CP: Central pair. Original figure, created with BioRender.com