When stimulated by the binding of specific chemicals, the membranes of taste bud receptors and olfactory neurons?

The answer is depolarization. Depolarization is the influx of cations, especially sodium ions, from the extracellular fluid into the neuron cell hence generation an electrical impulse along a neuron. The resting potential of neurons is - 70mV. When depolarized, the electronegativity in the inside of the neuron cell reduces.

Taste bud receptors if not stimulated are normally polarized. With the presence of the food, chemicals from the food bind with the cell protein which depolarized the cell membrane receptor. Depolarization will lead into the propagation of electric impulse. This will lead into the creation of sensory impulse. The larger number of the chemicals in the food will lead into a stronger impulse.