Ionic currents in molluscan soma
The present understanding of nerve excitability is founded on voltage clamp studies of axonal membranes. It has become clear, however, that the excitability of neuronal somata (cell bodies), dendrites, and terminal regions involves processes substantially different from those evident in axons. Somata, for instance, can exhibit a variety of slow oscillatory firing patterns and long lasting aftereffects of activity that are not observed in axonal preparations. In addition, voltage dependent calcium currents may play a major role in nerve excitability everywhere except the axon, perhaps in connection with the widespread intracellular messenger role of this ion (e.g. excitation-secretion coupling). The giant somata of the gastropod molluscs have so far yielded the most fundamental insights into the mechanisms of the distinctive electrical activity of nonaxonal membrane. It is our purpose here to review these insights.