FIGURE 4.25 Anatomy of Smell Along the roof of the nasal cavity, odorant molecules may bind to olfactory receptor neurons (ORNs) embedded in the olfactory epithelium. ORNs respond to a range of odors and, once activated, relay action potentials to the olfactory bulb, located just beneath the frontal lobes. The olfactory nerve projects directly into the forebrain.