Excitotoxicity is the pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate are overactivated. Pathologically high levels of glutamate can cause excitotoxicity by allowing high levels of calcium ions to enter the cell. Calcium influx into cells activates a number of enzymes. These enzymes go on to damage cell structures such as components of the cytoskeleton, membrane, and DNA.