Figure 1.

Circuit diagram of the mammalian olfactory bulb glomerular layer (two columns depicted). Olfactory sensory neurons (OSNs), housed in the olfactory epithelium of the nasal cavity (OE), project their axons into olfactory bulb. OSN axons expressing the same odorant receptor type converge to form glomeruli (shaded ovals) on the surface of the olfactory bulb, within which they interact with multiple classes of olfactory bulb principal neurons and interneurons. Principal neurons include mitral cells (Mi) and middle/deep tufted cells (often considered together with mitral cells; not shown). Glomerular interneurons include olfactory nerve-driven periglomerular cells (PGo), external tufted (ET) cell-driven periglomerular cells (PGe), and multiple subtypes of ET cells; both types of PG cells inhibit mitral cells. Superficial short-axon cells (sSA) are not associated with specific glomeruli but project broadly and laterally within the deep glomerular layer, interacting with glomerular interneurons. GL, glomerular layer; MCL, mitral cell layer. Deeper layers of olfactory bulb (Cleland, 2010) are not depicted.