The Science of Taste and Smell

Taste

Taste is a sensory function of the central nervous system, and is considered the weakest sense in the human body. The sense of taste begins with the taste buds, which are found in large bumps on the tongue called fungi form papillae. These can also be found elsewhere on the back of the throat and the palate, but the majority of taste buds are on the tongue. The fungi form papillae are mushroom shaped and, when stimulated, can swell. There are also little brush-shaped taste buds, called filiform papillae. Filiform papillae are the most numerous on the tongue, but they do not contain any taste buds.

Taste is detected by taste receptors cells, clustered in the taste buds. Taste buds are composed 50 to 150 taste receptor cells bundled together. The taste receptor cells are arranged so that the tip forms small taste pores, and through the pores extend microvillus, which bear taste receptors. In the taste cells are sensory nerves called taste nerves. When taste cells are stimulated, they transmit to the taste nerve fibers which transmit to the brain. There are 10,000 taste buds in the human mouth. Receptor cells for taste in humans are found on the surface of the tongue along the soft palate in the epithelium. There are two cranial nerves that help humans taste: the facial nerve, which stimulates the front of our tongue, and the glossopharyngeal nerve, which stimulates the back of the tongue. The vagus nerve carries information from the back of the tongue. The nerves send information from the tongue to the brain, identifying which taste is in the mouth.

Traditionally there are four primary tastes: sweet, salty, sour, and bitter. Sweet usually indicates foods of sugars and other proteins, like chocolate or fruit, which produces a pleasurable sensation. Bitter is usually thought to be unpleasant, like quinine, and is usually encountered in coffee and olives. Sour tastes are found in foods like lemons, and usually indicated the presence of absorbic acid. Saltiness typically indicates sodium ions, and is found in salty snacks like potato chips and pretzels. In recent years, a new taste has been entered into the lexicon, and is primarily found in Chinese and Japanese diets. It's called “unami”, and usually indicates a savory flavor, as found in meats and cheeses.


Smell

The sense of smell is what lets comprehend the scents and fragrances around them in everyday life.  When air is inhaled, it comes up through the nostrils over bones called turbinates, to millions of olfactory receptor neurons, which make up the olfactory epithelium. Each olfactory neuron has cilia, microscopic filaments that extend from the neuron with a protruding knob. This knob is the only part of the brain visible outside the skull. Molecules of odorants pass through the nasal passage and dissolve in mucus, and are detected by olfactory sensors. This occurs when odorants bind to odor proteins. The mucus in the epithelium contains salts, enzymes, and antibodies, which are important because they provide a direct route for infection to pass to the brain. The olfactory tract is a white band that is mostly nerve fibers going from the mitral cells to tufted cells in the olfactory bulb. The tract is close to the surface of the frontal lobe in the brain, and attached itself to the bottom of the cerebral hemisphere of the brain at the olfactory trigone. The tract then extends in the form of olfactory striae, which are three bands that stretch the olfactory tract beyond the olfactory trigone.

There are many olfaction disorders that somehow alter or prohibit the ways in which individuals can smell:

While uncommon, smell disorders do happen on ocassion. If olfactory disorders persist, see a doctor to discuss options and see what is behind the disorder.



Taste and Smell Working Together

Taste and smell are often loosely connected since both odor and food molecules get sense receptors working. The process of smell and taste begin with molecules meeting the nose or mouth. Molecules must dissolve in mucous in order stimulate cells, which send messages to brain. The brain then tells the human body how to interpret the stimulus. The two are so much related that if a person pinches their nose while eating and apple, onion, and potato, they will taste identical, because the human “memory” of each is imprinted on our brain by both smell and taste from the very first time contact.