Glomerular map: chemical feature coding in the olfactory bulb
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Glomeruli are spherical synaptic clusters (~100 ฮผm) in the olfactory bulb. Each receives input from thousands of olfactory sensory neurons (OSNs) expressing the same olfactory receptor. Humans have ~400 receptor types โ ~800 glomeruli (bilateral). The glomerular map is topographic: receptors detecting similar chemical features are spatially clustered.
Combinatorial coding: Each odor activates a unique subset of receptors/glomeruli โ the odor "fingerprint." Similar chemicals activate overlapping subsets. The mitral and tufted cells relay patterns to piriform cortex, where odor identity is decoded. Buck & Axel discovered olfactory receptors (Nobel 2004).