The neural control of heartbeat in invertebrates

• The cardiac ganglion reveals homeostatic mechanisms regulating electrical activity.
• The leech heartbeat system can be studied at all levels from neurons to circulation.
• In both systems individual variation is large, yet functional activity is maintained.

The neurogenic heartbeat of certain invertebrates has long been studied both as a way of understanding how automatic functions are regulated and for how neuronal networks generate the inherent rhythmic activity that controls and coordinates this vital function. This review focuses on the heartbeat of decapod crustaceans and hirudinid leeches, which remain important experimental systems for the exploration of central pattern generator networks, their properties, network and cellular mechanisms, modulation, and how animal-to-animal variation in neuronal and network properties are managed to produce functional output.