Even though cellular volume dynamics has been linked to cell apoptosis and intrinsic optical signals, there is no quantitative model for describing neuronal volume dynamics on the millisecond time scale. This study introduces a multiphysics neuron model, where the cell volume is a time-varying variable and multiple physical principles are combined to build governing equations. Using this model, we analyzed neuronal volume responses during excitation, which elucidated the variety of optical signals observed experimentally across the literature. Several physiological conditions were examined to investigate their effect on the pattern of volume response. In addition, we analyzed volume responses on a longer time scale with repetitive stimulation to study the characteristics of slow cell swelling. This multiscale analysis of the multiphysics model will provide not only a novel quantitative elucidation of physiologically important issues related with cellular volume dynamics but also a chance for further studies, such as the interesting possibility of inferring the balance of ion flux from plateau volume changes.