The olfactory bulb constitutes the first nerve relay of the olfactory system. This structure, located under the brain, receives axons from neurons in the olfactory epithelium that pass through the roof of the nasal cavity. Contrary to this pattern, which might suggest that olfactory neurons make dozens of contacts with each other, in reality each of them makes a single contact with a structure contained in the olfactory bulb called the olfactory glomerulus.