Q.How is polyspermy avoided in humans ?
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Start your 14-day free trial to unlock the full solution →Fusion of the first sperm triggers a fast electrical block and a cortical granule reaction that hardens the zona pellucida, preventing additional sperm from entering.
As soon as one sperm fuses with the oolemma (ovum's plasma membrane), an immediate change in membrane potential (the 'fast block') briefly makes the membrane resistant to further sperm fusion. This is quickly followed by the cortical reaction: cortical granules just beneath the ovum's plasma membrane release their contents by exocytosis into the space around the egg, altering the structure of the zona pellucida (the 'zona reaction') so that it becomes impenetrable to other sperm and any already-bound but unfused sperm are released. Together these fast and slow blocks ensure that only a single haploid sperm nucleus fuses with the egg nucleus, mainta …
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