We describe the origin and significance of electrical and mechanical observations on nerves. To this end, we compare two models for neural activity, which are the established HodgkinÐHuxley model and the more recent soliton theory, respectively. While the HodgkinÐHuxley model focuses particularly on the electrical aspects of the neural membranes, the soliton model is based on hydrodynamic and thermodynamic properties of the membrane, thus including changes in all thermodynamic variables.