At the few electrical synapses in the brain, gap junctions permit the arrival of an action potential at the synaptic terminals to be transmitted to the postsynaptic cell without the delay needed for release of a neurotransmitter . As the time of birth approaches, gap junctions between the smooth muscle cells of the uterus enable coordinated, powerful contractions to begin. Several inherited disorders of humans such as certain congenital heart defects and one form of congenital deafness have been found to be caused by mutant genes encoding connexins . Desmosomes Desmosomes are localized patches that hold two cells tightly together. Desmosomes are associated with intermediate filaments in the cytoplasm.
Carcinomas are cancers of epithelia.
However, the cells of carcinomas no longer have desmosomes. This may account for their ability to metastasize . Although each plant cell is encased in a boxlike cell wall, it turns out that communication between cells is just as easy, if not easier, than between animal cells. Fine strands of cytoplasm, called plasmodesmata , extend through pores in the cell wall connecting the cytoplasm of each cell with that of its neighbors. Plasmodesmata provide an easy route for the movement of ions, small molecules like sugars and amino acids, and even macromolecules like RNA between cells.