HUMAN SPERM ACROSOME REACTION - SCANNING ELECTRON MICROSCOPY

Ultrastructure of human sperm acrosome reaction steps, animated from a sequence of images taken with a scanning electron microscope. Only the acrosome - the anterior region of the sperm head - is involved. A reticulum of thin tubules appear first, giving the surface a wave-like appearance followed by the formation of small vesicles varied in size that gradually detach, a process that makes the intraacrosomal enzymes free to diffuse outside. These enzymes chemically drill the oocyte surface, ultimately allowing the spermatozoon to penetrate into and fertilize the female gamete. Magnification about 22,000X