Tongue diagram

Tongue with taste buds

The tongue has three different kinds of taste papillae with taste buds. The tip is covered with fungiform papillae. The photo shows the tip of a tongue with fungiform papillae. You can see the pores that lead food and beverage chemicals to the taste buds.
The sides of the tongue have foliate papillae that are like leaves lined with taste buds.
At the back of the tongue is a chevron of circumvallate papillae. They get their name from the fact that they stick up like a tower, surrounded by a valley or moat, that catches the liquids that you are swallowing and exposes them to the taste buds that line the sides of the "tower."
We also have a scattering of taste buds in the roof of our mouth and down our throat!
Each taste bud houses cells that respond to taste—sweet, sour, salty, umami, and bitter, and also some fats and minerals. The trigeminal nerve also has endings in taste buds that respond to texture, temperature, wetness, as well as to chemicals in what we eat.
People differ in the number of taste papillae and taste buds they have in their mouth, as well as the sensitivity of their taste cells to different chemicals in the foods. These differences lead to individual differences in taste sensitivity.

Diagram of the perception of smell in the nose and brain


This diagram shows the steps involved in perceiving smells.

  1. Odor chemicals either come directly through the nose (orthonasal) or via the back of the throat from food in the mouth (retronasal). They attach themselves to tiny hairs emanating from the olfactory bulb, and thus activate the nerve cells in the bulb. At this point novel odors are distinguished from background odors, and the novel messages are passed on.
  2. Messages from the olfactory bulb reach the pyriform cortex, where dominant odors are grouped into "odor objects." This grouping may lead to unexpected results. For example, tea can contain two chemicals, 2-phenylethanol and β-damascenone, that are found in most if not all honeys. Separately, each of these compounds has a rose-like floral aroma, but when present together in the right proportions they give a “honey” aroma to teas.
  3. From the pyriform cortex, odor messages are sent to the hippocampus where they activate memories, the amygdala where they are given an emotional "color," and the insula, where we can identify them, as, say, "honey."
  4. Odor messages then make their way to the orbit-frontal cortex, particularly on the right side of the brain, where all the information combines and we make the final decision as to what the order is and means, its importance, and whether it is good or bad.
  5. If the signal from the amygdala is ambiguous—in other words, if the overall smell contains both pleasant and unpleasant components and is therefore “hedonically complex”—the brain has a little more work to do to sort out its response. This is where the superior frontal cortex comes into play. Its activation in response to ambiguous signals is to make us pay more attention to the odor. Incidentally, perfumers make use of this ambiguity by including animalic compounds such as indole in their perfumes—these compounds have both alluring and disgusting qualities so we are likely to pay more attention to the wearer!

The trigeminal nerve

The trigeminal nerve reaches:

  • the eye,
  • the nose, including the olfactory patch,
  • the mouth including taste buds in the tongue and palate.
The trigeminal nerve senses temperature, texture, and wetness. In addition to these physical properties of foods, the trigeminal nerves responds to chemicals in food.
Activation of the nerve endings that respond to very hot and very cold leads to pain. For example, the capsaicin in chili peppers activate the hot receptors, which is why these peppers cause burning sensations. On the cold end of the spectrum, menthol activates the cool and cold receptors which is why mint pastilles containing extra high levels of menthol can cause pain as well.

Trigeminal receptors and the foods that activate them

Foods that activate the trigeminal temperature receptors

This diagram shows some of the foods that activate the trigeminal temperature receptors.
Because activation of one type of trigeminal receptor, say the "hot" receptor, can inhibit activation of another type of receptor, say the "cold" receptor, you can get more delicious pairing of teas (or wines!) with foods that activate the same receptors as the type of tea (or wine).
For example, the chemicals in green tea (for the most part) activate receptors at the "cool" and "cold" end of the spectrum, which is why green tea blends well with mint. By contrast, black teas will activate the "warm" and especially the "hot" receptors, so a black tea with a chocolate cake drizzled with raspberry coulis can taste so divine!