Difference between fast block to check polyspermy and slow block to check polyspermy

Dear Saket,

Theslow block to polyspermyin the sea urchin embryo consists of a physical barrier to further sperm penetration into the egg. Cortical granule exocytosis results in the formation of the fertilization envelope (often called the fertilization "membrane", even though the structure is not a true membrane)

Thefast block to polyspermyinvolves the opening of Na+ channels in the egg plasma membrane. Na+ flows into the egg cell, depolarizing the membrane. This depolarization prevents additional sperm from fusing to the egg plasma membrane.

Hope I answered your question