Understanding calcium waves and sparks in central neurons

All cells use changes in intracellular calcium concentration ([Ca2+](i)) to regulate cell signalling events. In neurons, with their elaborate dendritic and axonal arborizations, there are clear examples of both localized and widespread Ca2+ signals. [Ca2+](i) changes that are generated by Ca2+ entry through voltage- and ligand-gated channels are the best characterized. In addition, the release of Ca2+ from intracellular stores can result in increased [Ca2+](i); the signals that trigger this release have been less well-studied, in part because they are not usually associated with specific changes in membrane potential. However, recent experiments have revealed dramatic widespread Ca2+ waves and localized spark-like events, particularly in dendrites. Here we review emerging data on the nature of these signals and their functions.