taste bud

Meaning: A taste bud is a cluster of gustatory receptor cells found mostly inside the papillae of the tongue, with some on the palate and throat. Dissolved molecules called tastants bind receptors on these cells, which changes the cell's membrane potential and triggers sensory neurons. Signals travel through cranial nerves VII, IX and X to the brainstem, then the thalamus, then the gustatory cortex. The five basic tastes are sweet, sour, salty, bitter and umami (savory). Receptor cells are replaced regularly over time.

On the MCAT: Taste is classed as a chemical sense, along with smell, in sensation passages about transduction. Expect questions on supertasters, who have more papillae and taste buds and are especially sensitive to bitter tastes. Expect questions on flavor too: a stuffy nose dulls flavor because olfaction contributes much of what we call flavor. Taste aversion is a favorite link to learning. A food followed by nausea can become a conditioned stimulus after one pairing, which fits biological preparedness.

Common confusion: Students draw a tongue map with sweet at the tip and bitter at the back. That map is a myth. Each taste can be detected across the tongue, with only modest differences in sensitivity. Also, papillae are the visible bumps, and the taste buds are the receptor clusters within them.