Olfactory bulb

The olfactory bulb is the region in the brain receiving input from the olfactory neurons in the nasal olfactory epithelium. It is organized in glomeruli (one per smell) and innervates the dendrites of mitral cells that project to other forbrain regions including the olfactory cortex. Local circuits in the glomeruli and plexiform layers finetune the olfactory output information. It consists of the main olfactory bulb and the accessory olfactory bulb, involved in detection of pheromones.

Odor molecules is detected by the olfactory sensory neurons in the olfactory epithelium. The signal transduction starts at the olfactory receptors present on cilia of the sensory neuronal dendrites, covering the surfacte of the olfactory epithelium. Binding of the odor molecule triggers an electrical response and sensory signals to the olfactory nerve fiber. The olfactory nerve fibers pass through the plate of bone and connect the epithelium to the olfactory bulbs of the brain.

The glomeruli layer is organized into zones and clusters representing different spatial odors and is the first level of synaptic processing. The second level is the external plexiform layer, which mainly includes dendrites from the mitral cells, GABAergic granule cells, astrocytes and interneurons. Mitral cells is the third step in the processing, proving the output to the olfactory cortex, mitral cells receive information from the granule cell layer, located in the center of the olfactory bulb.