<Li> Internal plexiform layer </Li> <Li> Granule cell layer </Li> <P> The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell . As a neural circuit, the glomerular layer receives direct input from afferent nerves, made up of the axons from approximately ten 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 such that each glomerulus receives input primarily from olfactory receptor neurons that express the same olfactory receptor. The glomeruli layer of the olfactory bulb is the first level of synaptic processing . The glomeruli layer represents a spatial odor map organized by chemical structure of odorants like functional group and carbon chain length . This spatial map is divided into zones and clusters, which represent similar glomeruli and therefore similar odors . One cluster in particular is associated with rank, spoiled smells which are represented by certain chemical characteristics . This classification may be evolutionary to help identify food that is no longer good to eat . </P> <P> The spatial map of the glomeruli layer may be used for perception of odor in the olfactory cortex . The next level of synaptic processing in the olfactory bulb occurs in the external plexiform layer, between the glomerular layer and the mitral cell layer . The external plexiform layer contains astrocytes, interneurons and some mitral cells . It does not contain many cell bodies, rather mostly dendrites of mitral cells and GABAergic granule cells are also permeated by dendrites from neurons called mitral cells, which in turn output to the olfactory cortex . Numerous interneuron types exist in the olfactory bulb including periglomerular cells which synapse within and between glomeruli, and granule cells which synapse with mitral cells . The granule cell layer is the deepest layer in the olfactory bulb . It is made up of dendrodendritic granule cells that synapse to the mitral cell layer . </P>

What does the olfactory bulb do in the brain
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