Intercalated disks are cross-bands that separate the opposing ends of cardiac muscle cells. These bands are the result of elaborate junctions of membranes at the cell's boundary. They help to hold adjacent cells together and transmit the force of contraction from cell to cell. Intercellular junctions between the fused membranes of the intercalated disks allow diffusion of ions between the cells. This makes it possible for muscle impulses to travel rapidly from cell to cell.