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The olfactory bulb of the mouse is relatively large and is located at the frontal lobe of the brain posterior to the nasal cavity (see Diagram of Upper Nervous System – In Situ). It receives signals from the olfactory receptor neurons in the nasal epithelium (depicted in detail in Chapter 10. Sense Organs, Turbinate – Olfactory Epithelium) via the olfactory nerves and sends those to the olfactory cortex. In the olfactory bulb various layers can be distinguished. The axons of the olfactory neurons enter the outer layer of the olfactory bulb, the (olfactory) nerve fiber layer, organized into fascicles. The olfactory axons terminate in the glomerular layer, where they synapse with the dendrites of mitral cells, forming the spherical olfactory glomeruli. The external granular layer (which some scientists consider part of the glomerular layer) contains periglomerular cells, small interneurons whose dendrites form synapses with those of mitral and tufted cells. The external plexiform layer consists of the dendrites of mitral and a few tufted cells. The narrow mitral cell layer contains the miter-resembling cell bodies of mitral cells. The internal plexiform layer, like the external plexiform layer, has a low cell density. The internal granular layer, the layer closest to the olfactory tract, contains rows of mitral and tufted cell axons interspersed by rows of small round interneurons (granule cells). A medulla is found at the core of the olfactory bulb.
The 4X micrograph is a coronal section of the olfactory bulb, showing all layers of the olfactory bulb and the bone of the skull. The 10X micrograph exhibits the olfactory bulb layers in more detail. The 20X and 40X micrographs display the cells of several olfactory bulb layers. In the 40X micrograph the miter shape of the cell bodies of the mitral cells is visible.
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