We consider the propagation of intense femtosecond pulses in a dielectric medium with an induced plasma. This plasma is excited by the strong electric field of the pulses, stimulating sequential electron transition to the conductivity band through excited discrete energy states. It is demonstrated that this simple dynamic model of ultrashort optical pulse propagation in a dielectric medium with self-induced plasma can be applied to experiments on the superbroadening of the pulse spectrum into the long-wavelength range, including terahertz generation, as well as the generation of high-order harmonics.