Figure 1: Scheme showing the three main mechanisms associated to the initial events of oocyte fertilization. Sperm entry through the acrosomic reaction liberates the genetic material into the oocyte and triggers the local entrance of external calcium and the subsequent propagation of a calcium wave through the ooplasm. This process activates protein motors, that actively transport clusters of cortical vesicles towards the plasmatic membrane. Once fused, hyaline is released and initiates the gradual activation of the vitaline envelope until the shield against polyspermy is completed.