olfactory epithelium

Meaning: The olfactory epithelium is a small patch of tissue high in the nasal cavity that holds the receptor cells for smell. Its olfactory receptor neurons are chemoreceptors: odorant molecules dissolve in mucus, bind receptors on the neurons' cilia, and trigger action potentials. Their axons pass through the cribriform plate to the olfactory bulb, which sends signals to the olfactory cortex, amygdala, and hippocampus.

On the MCAT: Passages ask you to trace the pathway from nose to brain and to compare it with other senses. Olfactory signals reach the cortex without a thalamic relay first, unlike vision, hearing, and touch. The direct links to the amygdala and hippocampus are the usual explanation for why smells evoke strong emotions and vivid memories. A given odor activates a pattern across many receptor types, and prolonged exposure to a steady odor produces sensory adaptation, so it seems weaker over time.

Common confusion: The receptors are not in the olfactory bulb. The bulb is brain tissue that receives their axons, and transduction happens in the epithelium. Smell and taste are both chemical senses, but taste relies on taste buds on the tongue, and its signals do pass through the thalamus.