We propose a model for the low-temperature excitations in glasses, which have been the object of recent investigations by means of nonlinear optical techniques. The experimental evidence strongly suggests the presence in these amorphous materials of configurational two-level systems, which are coupled via the phonon field to the chromophore whose optical response is being probed. A microscopic description for the relevant interactions is developed and the connections between the exact dynamics within this description and the stochastic sudden-jump model are drawn by means of a path integral method.