POLYSPERMY AND ITS TYPES

 

FAST BLOCK POLYSPERMY

In the fast block polyspermy sodium ions which are resting the potential membrane rises and sperm can no longer fuse with the egg.

·         In fast block 1-3 seconds after sperm binds with the egg no further sperm can fuse with egg.

·         NA+ diffuses into the oocyte from extracellular space on the contact of first sperm

·         The depolarization membrane prevents additional sperm from fusing with the oocyte membrane.

·         Polyspermy can be blocked without an electrical block, this is achieved by establishing a mechanical barrier to polyspermy.

·         Sea urchin have two step polyspermy prevention strategy.

Slow block polyspermy

Slow block polyspermy includes the modification of the zona proteins by the contents of the cortical granules. So the sperm can no longer bind with zona

·         In slow block polyspermy occurs after one minute of fusion of egg –sperm

·         Slow block in sea urchin is slower and permanent block.

·         When the sperm enters cortical granules fuse with cell membranes and release several molecules.

·         Sperms which are attached to receptors are forced to detach.

·         In slow block the zona pellucida is modified by serine proteases which are released by cortical granules. These proteases destroys the protein links between membrane and vitelline envelop, this removes other sperms bound to and helps to form the fertilization envelop from cortical granules.