So basically, these ions flow across the cell membrane from a high concentration to low concentration gradient. And the opening of these channels is a result of the binding of some type of stimulatory molecule. And this stimulatory molecule is known as a ligand. So ligand gated ion channels are these channels that respond to the binding of a special type of molecule. And once that molecule binds, so let's say this green molecule is the ligand, it binds onto the outer portion of this transmembrane protein we call a ligand gated ion channel. Once it binds, let's say, on the outside, it causes a conformational change that opens up the internal pocket of that particular transmembrane protein.