We will study synaptic integration, regional membrane properties, and control of internal calcium in neurons of the supraesophageal ganglion of the giant barnacle, Balanus nubilus and the stomatogastric ganglion of the crab, Cancer borealis. Many of the interesting aspects of these problems occur on the dendrites or presynaptic terminals of these cells and therefore cannot be easily examined with microelectrodes. Therefore we will employ optical methods which we have been developing to examine these previously inaccessible regions. Using both voltage sensitive dyes and calcium indicator dyes we will map the spread of electrical potentials and properties of calcium transients simultaneously throughout these neurons. From these measurements we will determine the passive membrane properties at many locations, regional variations in ionic conductance mechanisms, synapse locations and the propagation of synaptic and action potentials in the cell. In addition, the threshold and time course of calcium transients will be examined to reveal regional variations in the properties of calcium channels and calcium buffering mechanisms. Both the techniques we develop and the conclusions we reach should be of general value in understanding cellular and synaptic mechanisms in a wide variety of preparations, from single neurons in culture to neurons in the mammalian brain.