Structure of Formed Sperm

Sperm are smaller than most cells in the body; in fact, the volume of a sperm cell is 85,000 times less than that of the female gamete. Approximately 100 to 300 million sperm are produced each day; whereas, women typically ovulate only one oocyte per month. Sperm have a distinctive head, mid-piece, and tail region (Figure). The head of the sperm contains the extremely compact  nucleus with very little cytoplasm. These qualities contribute to the overall small size of the sperm (the head is only 5 μm long). A structure called the acrosome covers most of the head of the sperm cell as a “cap” that is filled with enzymes important for preparing sperm to participate in fertilization. The flagellum extends from the neck and the mid-piece through the tail of the sperm enabling it to move the entire sperm cell. The central strand of the flagellum is formed from inside the maturing sperm cell during the final stages of spermatogenesis.

Structure of Sperm

This diagram shows the structure of sperm; the major parts are labeled.  Sperm cells are divided into a head, containing DNA; a mid-piece, containing mitochondria; and a tail, providing motility. The acrosome is oval and somewhat flattened.

To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.