Olfaction, the sense of smell, is the one sense that can provoke the fastest responses. Just walk into the kitchen while your mother or father is preparing your favorite meal. Very likely, you know what was cooking when you hit the front door, and your mouth was watering by time you reached the kitchen. If have also experienced the opposite reaction, whether someone dropped a stink bomb, you smelled a particularly bad smelling perfume.

Odors, chemical molecules, floating in the air enter the nose, dissolving in the mucous of the olfactory epithelium, the membrane covering the superior (upper portion) nasal cavity and septum. Here, olfactory cells bind to the odors, sending a messages of delicious, noxious, or bland smells through the olfactory nerves, then to the olfactory bulb, which lies just on the other side of the skull, opposite the foramen. From the olfactory bulb, the messages of odors finally are sent to the brain.