Neurons in Action 2 is the second version of a unique CD-ROM-based learning tool that combines hyperlinked text with NEURON simulations of laboratory experiments in neurophysiology. Version 2 features nine new tutorials introducing new channel types, single channel simulations, and a redesigned interface. Neurons in Action's moving graphs provide insight into nerve function that is simply not possible with conventional, static text and figure presentations. Students discover how changing parameters such a neuronal geometry, ion concentrations, ion channel densities, and degree of myelination affects the generation of action potentials, synaptic potentials, and the spread or propagation of voltages within a neuron. For instructors, minimovies of NEURON simulations are provided for use in lectures.