The olfactory bulb receives direct input from the axons of approximately 10 million olfactory receptor neurons in the olfactory mucosa, a region of the nasal cavity. The ends of the axons cluster in spherical structures known as glomeruli (of which there are between 1000 and 2000), and each glomerulus receives input primarily from a single type of ORN. These glomeruli are permeated by dendritic inputs to neurons known as mitral cells, which in turn output to the olfactory cortex. Mitral cells are connected by interneurons known as granule cells, which seem to produce a sort of lateral inhibition between mitral cells. It is not yet fully known what the functional role of this lateral inhibition is.