And when this happens, two important processes take place. First of all, the plasma membrane of the excel begins to depolarize and that's because we have many ion channels along the plasma membrane of the xcel that begin to open up. For example, sodium ion channels begin to open up and sodium ions begin to flow into the cell and that depolarizes the plasma membrane. What also happens is calcium ions also flow into our cytoplasm as a result of the opening of those channels, ion channels. And when calcium concentration increases inside the cytoplasm of the cell these granules, these vesicles we call cortical vesicles begin to fuse with the membrane of our excel. And via this exocytosis process the enzymes within these cortical granules are released into the zonapolucida.