How is it that the potassium ion channel actually blocks the movement of this smaller sodium ion? Well, the answer lies in this salvation cage. So we saw that in the case for potassium, when potassium loses this salvation cage, that requires an input of energy. But because of the size of the potassium, because of it being just the perfect radius, just the perfect size, it can form these intermolecular interactions, which are overall more stable than these intermolecular interactions. And so the sum of those two values produces a negative free energy, and this reaction takes place spontaneously. Now, in the case of the sodium ions, this is what we basically see.