The theory of optical parametric oscillation internal to the laser cavity is extended to include the dynamics of the population inversion of the laser medium, thus generalizing it to include all laser-oscillator systems. The equations of motion of the oscillator-laser system are solved by digital computer for the case of a -switched Nd:YAG laser with a LiNbO3parametric oscillator inside the laser cavity. It is found that this internal optical parametric oscillator operates in a spiking regime, with one or more oscillator pulses per pump pulse. The oscillator pulses inside the nonlinear crystal are often more intense than the laser pulse that would have existed in the absence of parametric oscillation. Oscillator pulse lengths are much shorter than the laser pulse length, with oscillator pulse lengths of typically 5-10 ns compared to laser pulse lengths of 200 ns. The repetition rate of the oscillator pulses is pump-power dependent, with the pulses occurring more frequently as the laser field increases. The theoretical results are compared with experiment, and the analysis is found to provide a good qualitative description of the -switched parametric oscillator.