Figure 1.

Left: Simplified diagram of the main olfactory bulb to illustrate its different layers, mitral cells (MCs), granule cells (GCs), and centrifugal fibers (CFF). The olfactory nerve layer (ONL) contains the axons of olfactory receptor neurons, which synapse in the spheroidal glomeruli on MCs, and other neurons. For clarity, glomerular layer (GL) cell types have been omitted from the diagram. The dendrites of the mitral cells pass from the GL through the external plexiform layer (EPL) into the mitral cell layer (MCL) which contains the cell bodies of mitral cells and many granule cells. The internal plexiform layer (IPL) contains the axons of the principal output cells (mitral cells and tufted cells) as they course to cortical areas. The granule cell layer (GCL) contains most of the granule cells as well as other inhibitory cells. CFF bring modulatory feedback signals from cortical areas, to synapse in the glomerular layer and granule cell layer. EPL, IPL—external, internal plexiform layer. Right: Adult mouse main olfactory bulb section with a single mitral cell intracellularly filled with biocytin (red) and nuclei stained with counterstain Sytox Green (green). The mitral cell soma is located in the MCL. One apical dendrite reaches into one glomerulus and several lateral dendrites span the main olfactory bulb. Modified from [3].