The olfactory bulb receives primary afferent input from the sensory neurons lining the lumen of the nasal cavity. Within the synaptic circuitry of the olfactory bulb two primary populations of projection neurons, mitral and tufted cells, and several populations of interneurons, including granule and peri/juxtaglomerular cells, process the arriving odor information. The molecular specificity of the olfactory system, established with the expression of only one odor receptor by the sensory neurons, is preserved in the olfactory bulb by the convergence of sensory axons expressing the same odor receptor into specific glomeruli. In turn, because the projection neurons arborize their apical dendrite in only one glomerulus, the specificity of odor processing continues as the information is processed further in the local synaptic circuits found in the olfactory bulb. The morphology and organization of the cells in the olfactory bulb, including the specificity and spatial distribution of their synaptic connections, are explored in this chapter.
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