So gap junctions are the connective tunnels that exist between adjacent cells. So these types of tunnels, these types of channels or gap junctions, allow the movement of different types of molecules and ions up to a certain size, usually up to 1000 deltons. So they allow molecules and ions up to a certain size to pass from one cell to the other cell. So these are our examples of our gap junctions. For example, if calcium ions want to get from this cell to this cell, they could move via these intracellular connections known as gap junctions. Now, what's a particular example of a cell that contains gap junctions?