olfactory bulb

Meaning: Odorant molecules bind receptors on olfactory receptor neurons in the olfactory epithelium of the upper nasal cavity. Their axons pass through the cribriform plate of the skull and synapse in the olfactory bulb, in clusters called glomeruli, onto mitral cells. Mitral cell axons form the olfactory tract, which projects to the olfactory cortex, the amygdala, and hippocampal regions. Because these targets belong to the limbic system, smell is closely linked to emotion and memory.

On the MCAT: Expect a question on sensory pathways asking which sense reaches the cortex without first being relayed through the thalamus (olfaction, in the standard account). Passages may describe loss of smell after damage to the bulb or cribriform plate, or a vivid memory triggered by an odor, and ask which structures explain it. Another common item compares the pathways for vision, hearing, taste, and smell.

Common confusion: Students place the odor receptors in the bulb. The receptors are in the nasal epithelium; the bulb is the first processing station inside the brain. Students also assume every sense passes through the thalamus. Vision, hearing, touch, and taste do, while smell is the usual exception.