Hi Accutron,
I have a pretty strong background in physiology (am finishing my degree in a few weeks) and starting medicine next year so maybe I can give a little more insight on that perspective. The electrical signalling you are referring to is that between nerve cells and their target cells right? That's the inference I get from synapse.
It's true that you won't have a fully developed neural system (or any development at all actually) at conception, however the basic premise of cell signalling remains, largely, K+ out, Na+ in. This happens on a cellular level, even without the presence of specialized nerve cells. This hyper polarization is required for most (any) cell to function and as such the brain, at any stage of development cannot be just a lump of cells. It is not as though suddenly it turns on and the ability to signal jumps into action. It is a slow process of neural development which eventually leads to what you see as a neural impulse today.