FIGURE 1.

Normal sperm morphology and ultrastructure. Sperm is divided into the sperm head and flagellum. The flagellum is subdivided into the following three parts: midpiece, principal piece and end piece. The centrosome is divided into proximal and distal centrioles, which attach to the basal plate at the implantation fossa and form the axoneme. The axoneme crosses through the entire flagellum. In the midpiece and principal piece, the axoneme is surrounded by outer dense fibers. The midpiece also consists of a mitochondrial sheath surrounding the axoneme, which is replaced by the fibrous sheath in the principal piece. There is no periaxonemal structure in the end piece.