Practice question

Fast block to polyspermy prevents immediate entry of extra sperm within seconds of first fusion. Sperm-egg fusion depolarizes plasma membrane from about -70 mV to +20 mV via rapid Na+ channels, creating electrical barrier because voltage-sensitive sperm fusion cannot merge with depolarized membrane. This depolarization occurs within one second and persists roughly one minute until permanent slow block develops via fertilization envelope. Cortical granule exocytosis, protease release constitute slow block acting later. Fast electrical block thus provides initial transient defense ensuring monospermy before permanent barrier assembles.