chapter 14

labeled lines

A theory of taste coding in which each taste nerve fiber carries a particular taste quality. For example, the quality evoked from a sucrose-best fiber is sweet, that from an NaCl-best fiber is salty, and so on.

taster of PTC/PROP

An individual born with one or both dominant alleles for the Tas2r38 gene and able to taste the compounds phenylthiocarbamide and propylthiouracil. Tasters of PTC/PROP who also have a high density of fungiform papillae are supertasters.

nontaster of PTC/PROP

An individual born with two recessive alleles for the Tas2r38 gene and unable to taste the compounds phenylthiocarbamide or propylthiouracil.

supertaster

An individual who perceives the most intense taste sensations. A variety of factors may contribute to this heightened perception; among the most important is the density of fungiform papillae.

tastant

Any stimulus that can be tasted.

taste receptor cells

Cells within the taste bud that contain sites on their apical projections that can interact with taste stimuli. These sites fall into two major categories: those interacting with charged particles (e.g., sodium and hydrogen ions), and those interacting with specific chemical structures.

circumvallate papillae

Circular structures that form an inverted V on the rear of the tongue (three to five on each side). Circumvallate papillae are moundlike structures surrounded by a trench (like a moat). These papillae are much larger than fungiform papillae.

foliate papillae

Folds of tissue containing taste buds. Foliate papillae are located on the rear of the tongue lateral to the circumvallate papillae, where the tongue attaches to the mouth.

taste buds

Globular clusters of cells that have the function of creating the neural signals conveyed to the brain by taste nerves. Some of the cells in the taste bud have specialized sites on their apical projections that interact with taste stimuli. Some of the cells form synapses with taste nerve fibers.

fungiform papillae

Mushroom-shaped structures (maximum diameter 1 millimeter) that are distributed most densely on the edges of the tongue, especially the tip. Taste buds (an average of six per papilla) are buried in the surface.

microvilli

Slender projections on the tips of some taste bud cells that extend into the taste pore.

filiform papillae

Small structures on the tongue that provide most of the bumpy appearance. Filiform papillae have no taste function.

papillae

Structures that give the tongue its bumpy appearance. From smallest to largest, the papillae types that contain taste buds are fungiform, foliate, and circumvallate; filiform papillae, which do not contain taste buds, are the smallest and most numerous.

cross-modality matching

The ability to match the intensities of sensations that come from different sensory modalities. This ability enables insight into sensory differences. To the average nontaster of PTC/PROP, for example, the bitterness of black coffee roughly matches the pain of a mild headache; for a supertaster, the bitterness of black coffee roughly matches the pain of a severe headache

chorda tympani

The branch of cranial nerve VII (the facial nerve) that carries taste information from the anterior, mobile tongue (the part that can be stuck out). The chorda tympani nerve leaves the tongue with the lingual branch of the trigeminal nerve (cranial nerve V) and then passes through the middle ear on its way to the brain.

flavor

The combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction.

basic tastes

The four taste qualities that are generally agreed to describe human taste experience: sweet, salty, sour, and bitter.

specific hungers theory

The idea that deficiency of a given nutrient produces craving (a specific hunger) for that nutrient. Curt Richter first proposed this idea and demonstrated that cravings for salty or for sweet are associated with deficiencies in those substances. However, the idea proved wrong for other nutrients (e.g., vitamins).

orbitofrontal cortex

The part of the frontal lobe of the cortex that lies above the bone (orbit) containing the eyes.

insular cortex

The primary cortical processing area for taste—the part of the cortex that first receives taste information.

retronasal olfactory sensation

The sensation of an odor that is perceived when chewing and swallowing force an odorant in the mouth up behind the palate into the nose. Such odor sensations are perceived as originating from the mouth, even though the actual contact of odorant and receptor occurs at the olfactory mucosa.

monosodium glutamate (MSG)

The sodium salt of glutamic acid (an amino acid).

sweet

The taste quality produced by some sugars, such as glucose, fructose, and sucrose. These three sugars are particularly biologically useful to us, and our sweet receptors are tuned to them. Some other compounds (e.g., saccharin, aspartame), are also sweet.

salty

The taste quality produced by the cations of salts (e.g., the sodium in sodium chloride produces the salty taste). Some cations also produce other taste qualities (e.g., potassium tastes bitter as well as salty). The purest salty taste is produced by sodium chloride (NaCl), common table salt.

sour

The taste quality produced by the hydrogen ion in acids.

bitter

The taste quality, generally considered unpleasant, produced by substances like quinine or caffeine.

umami

The taste sensation evoked by monosodium glutamate.

cranial nerves

Twelve pairs of nerves (one from each pair for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull.