The olfactory bulb is the first processing station for smell signals entering the human brain.
Odor-detecting receptor cells in the nasal epithelium send axons through tiny openings in the cribriform plate, a bone forming part of the skull. These axons terminate in spherical structures called glomeruli inside the olfactory bulb. Neurons in the bulb then organize and relay odor information to regions including the olfactory cortex.
The olfactory bulb is unusual because smell information reaches the cerebral cortex without first making the standard thalamic relay used by most other sensory systems. However, the thalamus still participates in later aspects of odor attention and perception.
A common mix-up is calling the olfactory nerve the bulb. The olfactory nerve consists of the receptor-cell axons, whereas the bulb is brain tissue that performs early processing. Humans have two olfactory bulbs, one above each nasal cavity.