gap junction, a type of junction between cells, consisting of a narrowed portion of the intercellular space that contains channels or pores composed of hexagonal arrays of membrane-spanning proteins around a central lumen (connexon), through which pass ions and small molecules. In electrically excitable tissues such as myocardial tissue and the central nervous system, gap junctions serve to transmit electrical impulses by movement of ions and are known as electrotonic synapses. Also called nexus. See also connexon.
