During the cortical reaction, during the cortical reaction, enzymes are released from the head of the sperm enzymes are released from vesicles in the oocyte the zona pellucida disappears multiple sperm fertilize the egg

During the cortical reaction, enzymes are released from vesicles in the oocyte. The cortical reaction is a reaction for preventing polyspermy, the fusion of multiple sperm with one egg. It is a process which occurs during fertilization by the release of cortical granules from the egg. Cortical granules contain components which establish a permanent barrier to sperm entry.