reactions

• acrosome

  1. ovum releases chemokines that attract sperm
  2. receptors in sperm head bind to ZP
  3. acrosome swells in head, acrosome membrane fusing with sperm cell membrane
  4. digestive enzymes released from acrosome
  5. ZP is hydrolysed by enzymes so sperm head can reach and bind to fuse with the ovum membrane
  6. genetic material in nucleus of one sperm passes through membrane and enters ovum
• cortical

  1. genetic material from sperm head enters ovum
  2. lysosomes in ovum release cortical granules in the cytoplasm and fuse with the cell surface, releasing enzymes into ZP
  3. ZP hardens, preventing polyspermy
  4. overall change in charge across egg cell membrane
  5. egg can fuse with sperm so fertilisation complete