what is the difference between fast block polyspermy and slow block polyspermy

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The fast block to polyspermy, which has been best studied in sea urchins, consists of a rapid electrical depolarization of the plasma membrane of the egg. The resting membrane potential of the egg changes from about − 70 to + 10 mV within 2–3 s after fusion of the spermatozoon with the egg.

Whereas the slow block to polyspermy in the sea urchin embryo consists of a physical barrier to further sperm penetration into the egg. The fertilization envelope is formed by the lifting of the vitelline envelope away from the egg plasma membrane.

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