How is poly embryony checked during fertillization in humans ?

Explanation

Binding of the sperm head to the egg membrane induces depolarization of the egg plasma membrane Depolarization causes fast block to polyspermy, that checks additional sperms from joining the egg's plasma membrane .
Immediately after the fustion of sperm and egg plasma membranes , the egg shows a cortical reaction to further check the entry of more sperms .In this reaction , the cortical granules present beneath the egg's plasma membrane fuse with the plasma membrane and release their enzymes between the plasma membrane and zona pellucida these enzymes harden the zona pellucida which now acts as the sure block to polyembryony .