Question

please explain about the fertilization, after the sperm enter the egg, what will happen to the membrane potential of the egg to block other sperms

Answer 1

A single egg is surrounded by many sperms attached to it. It is very important that only one of the sperm should be fused with the membrane to deliver the sperm nucleus inside the egg cell for fusion. Egg cells are equipped with a mechanism that prevents polyspermy known as 'a fast block to polyspermy'.
Before the adding of the sperm cell, the membrane potential of the egg cell is maintained around -70mv. Within 1 to 3 seconds of the entry of sperm nucleus inside the egg the membrane potential shifts to a positive direction. The rapid depolarization of the egg cell membrane is due to the influx of Na+ ions preventing additional sperm cell to fuse with the egg cell.