Spermatozoa (sperm)

A group of sperm, with detail of a single sperm.

Spermatozoa (sperm) are the male sex cells that carry genetic material. They are so tiny that they can't be seen without a microscope. One ejaculation usually contains between 20 million and 600 million sperm.

Sperm have an oval head, a short middle, and a long tail. They move by whipping their tails. A sperm fertilizes an egg (ovum) by breaking through the membrane that surrounds the egg.

Sperm develop in the testicles. They are added to semen before ejaculation.

Current as of: March 1, 2023

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Avery L. Seifert MD - Urology
Kara C. Taggart MD - Urology
JoLynn Montgomery PA - Family Medicine

The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.