And the first contact that takes place between the sperm cell and our exile takes place at the zona pellucida. So when the sperm cell contacts the egg, it interacts first with this layer of glycoproteins known as the zona pellucida. And what happens is the acrosome structure found on the apex, on the tip of that sperm cell releases these digestive enzymes that begin digesting a hole in the zona pellucida. 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.