How does a refrigerator work?

This will probably seem stupid, but I really don't know how a refrigerator works. I sprayed insecticide (boric acid powder) behind my refrigerator. Is there anyway there is a hole or vent or something back there that will allow the poison to get into the food in the fridge when sprayed? My fridge has the freezer on the bottom. I know this probably sounds dumb, but I worry about dumb things like this and figure it doesn't hurt to ask. Is the food storage part of the fridge and freezer sealed? If so, how does the food get cold?