In other species, the acrosomal protein bindin binds specifically to bindin receptors on the respective eggs. The electrical polarity of the egg membrane reverses in 0.1 second and this prevents any more sperm from fusing with the egg. This occurs in sea urchins and frogs, but not most mammals. Cortical granules discharge and the swelling of their contents raises a fertilization membrane in many animals . In mammals, enzymes released from the cortical granules disable sperm receptors in the zona pellucida.
Fertilization activates the egg to complete meiosis and begin development.
The above responses ensue from calcium flux of fertilization. Calcium changes affect many factors established in egg during maturation. Nancy J. Alexander Page 136-143 More than half the world's couples practice birth control. Dissatisfaction with current methods is high, leading to misuse or abandonment of contraceptive techniques, and contributing significantly to accidental pregnancy and to abortion. In the U.S., more than half of all pregnancies every year are unintended.