Ch. 15

Question 1

taste

Answer 1

sensations evoked by solutions in the mouth that contact receptors on the tongue and the roof of the mouth that then connect to axons in cranial nerves VII, IX, and X

Question 2

flavor

Answer 2

sensations that are produced by retronasal olfaction

Question 3

retronasal olfactory sensation

Answer 3

the sensation of an odorant that is perceived when chewing and swallowing force that 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

Question 4

chorda tympani

Answer 4

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); exits 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
- in a study where participants’ chorda tympanis were anesthetized, they were able to smell food but not taste it

Question 5

sequence of events for taste perception

Answer 5

• Chewing breaks down food substances into molecules, which are dissolved in saliva
• Saliva-borne food molecules flow into taste pores that lead to the taste buds housed in papillae that are located mostly on the tongue in a rough oval
• Taste buds contain multiple taste receptor cells, each of which responds to a limited number of molecule types → when a taste receptor cell comes in contact with one of its preferred molecules, it creates a message that travels along one of the cranial nerves to the brain

Question 6

taste bud

Answer 6

a globular cluster of cells that has the function of creating neural signals conveyed to the brain by the taste nerves

Question 7

papilla

Answer 7

any of multiple structures that give the tongue its bumpy appearance

Question 8

four major varieties of papillae

Answer 8

filiform, fungiform, foliate, circumvallate

Question 9

filiform papillae

Answer 9

small structures on the tongue that provide most of the bumpy appearance; have no taste function (do not contain taste buds); most numerous of the papillae

Question 10

fungiform papillae

Answer 10

mushroom-shaped structures (maximum diameter 1 mm) that are distributed most densely on the edges of the tongue, especially the tip; taste buds (an average of six per papilla) are buried on the surface

Question 11

foliate papillae

Answer 11

folds of tissue containing taste buds; located on the rear of the tongue lateral to the circumvallate papillae, where the tongue attached to the mouth

Question 12

circumvallate papillae

Answer 12

circular structures that form an inverted V on the rear of the tongue (three to five on each side, with the largest in the center); moundlike structures, each surrounded by a trench (like a moat)
- taste buds buried in the side of the moats

Question 13

taste receptor cell

Answer 13

a cell within the taste bud that contains sites on its apical projections (microvilli) that can interact with taste stimuli

Question 14

two major categories of taste receptor cells

Answer 14

• those interacting with charged particles
• G protein-coupled receptors that interact with sweet and bitter stimuli

Question 15

supertasters

Answer 15

those individuals whose perception of taste sensations is the most intense; variety of factors may contribute to this heightened perception, including density of fungiform papillae
- tend to have the most fungiform papillae and thus the most taste buds
- experience the most intense sensations of oral burn and oral touch

Question 16

taste bud locations

Answer 16

distributed in a line across the roof of the mouth and in papillae distributed in an oval on the tongue

Question 17

taste myth of the tongue map

Answer 17

• a paper published measuring taste thresholds for bitter, sweet, salty, and sour all around the tongue
• taste thresholds do vary across different tongue locations, but that variation is quite small
• thresholds do not predict taste intensities in the real world

Question 18

taste buds and taste receptor cells

Answer 18

each taste bud is a cluster of elongated cells
- The tips of some of these cells end in slender microvilli, containing sites that bind to taste substances

Question 19

microvilli

Answer 19

slender projections of the cell membrane on the tips of some taste bud cells that extend into the taste pore

Question 20

three groups of taste bud cells

Answer 20

Type I Cells, Type II Cells, Type III Cells

Question 21

Type I Cells (taste bud cells)

Answer 21

majority of taste bud cells; appear to have primarily housekeeping functions

Question 22

Type II Cells (taste bud cells)

Answer 22

express G protein-coupled receptors (GPCRs) that wind back and forth seven times across the microvillus membrane; express GPCRs either for sweet or for bitter
- When a particular tastant molecule “key” is fitted into the “lock” portion of a GPCR on the outside of the membrane, the portion of the GPCR inside the cell starts a cascade of molecular events

Question 23

Type III Cells (taste bud cells)

Answer 23

smallest number of cells; have synapses and appear to mediate sour taste

Question 24

tastant

Answer 24

any stimulus that can be tasted

Question 25

taste receptors and limited life span

Answer 25

- After a matter of days, they die and are replaced by new cells - This constant renewal enables the taste system to recover from damage and explains why our taste systems can remain robust even into old age

Question 26

taste information traveling to the brain

Answer 26

- this information travels in branches of three cranial nerves: chorda tympani and greater superficial petrosal, glossopharyngeal, and vagus - information travels through the medulla and thalamus before reaching the insular cortex - orbitofrontal cortex (OFC) receives projections from the insular cortex

Question 27

cranial nerves

Answer 27

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

Question 28

insular cortex

Answer 28

the primary cortical processing area for taste; part of the cortex that first receives taste information

Question 29

orbitofrontal cortex (OFC)

Answer 29

the part of the frontal lobe of the cortex that lies behind the bone (orbit) containing the eyes; involved in many functions and is responsible for the conscious experience of olfactions as well as the integration of pleasure and displeasure from food

Question 30

inhibition plays an important role in the processing of taste information in the brain

Answer 30

- One of the functions of this inhibition may be to protect our whole-mouth perception of taste in the face of injuries to the taste system - The brain receives taste input bilaterally from three cranial nerves; damage to one of these nerves diminishes its contribution to the whole; however that damage also releases the inhibition that is normally produced by the damaged nerve → result is that whole-mouth taste intensities are relatively unchanged - Inhibition of pain perceptions by taste-processing parts of the brain would make eating easier in face of mouth injuries

Question 31

basic taste

Answer 31

any of the four taste qualities that are generally agreed to describe human taste experience: sweet, salty, sour, bitter - our liking and disliking for them is hardwired in the brain --> important for biological purposes

Question 32

salty

Answer 32

one of the four basic tastes; the taste quality produced by the cations of salts - purest salty taste produced by sodium chloride (NaCl), common table salt

Question 33

sour

Answer 33

one of the four basic tastes; the taste quality produced by the hydrogen ion in acids

Question 34

bitter

Answer 34

one of the four basic tastes; the taste quality produced by substances like quinine or caffeine - some of the T2 receptors respond only to specific compounds whereas others are bitter "generalists" that respond to many compounds - biological function is to encourage us to avoid that food

Question 35

sweet

Answer 35

one of the four basic tastes; the taste quality produced by some sugars, such as glucose, fructose, ad sucrose - biological function is to tune receptors such that the biologically important sugars stimulate sweet taste but others do not - Only two GPCRs of the type II taste receptor cells are involved with sweet taste— TAS1R2 and TAS1R3

Question 36

two new tastes that investigators have suggested adding to the list of basic tastes

Answer 36

umami and fatty

Question 37

basic tastes divided into two major groups

Answer 37

- Salty and sour, mediated by ion channels (small openings in the membranes of the microvilli in taste bud receptor cells) - Bitter and sweet, mediated by protein receptors (GCPRs in the membranes of the microvilli)

Question 38

heterodimer

Answer 38

a chain of two molecules (a dimer) that are different from each other; binds sucrose, glucose, and fructose, but also binds a variety of other compounds on different sites - Formed by the combination of TAS1R2 and TAS1R3

Question 39

homodimer

Answer 39

can be formed from two TAS1R3 molecules → respond only to high concentrations of sugars - This receptor would help the brain tell the difference between sugars and artificial sweeteners

Question 40

umami

Answer 40

the taste sensation produced by monosodium glutamate

Question 41

monosoidum glutamate (MSG)

Answer 41

the sodium salt of glutamic acid (an amino acid)

Question 42

how umami rose as a candidate as a fifth basic taste

Answer 42

- Initially marketed as a flavor enhancer, said to suppress unpleasant tastes and enhance pleasant ones - Next claim was that MSG was a fifth basic taste, speculating that it signaled protein and thus played an important role in nutrition (however, it has been determined that protein molecules are too large to stimulate taste or olfaction)

Question 43

these molecules cannot stimulate taste or olfaction because they are too large

Answer 43

proteins and fats

Question 44

nontaster (of PTC/PROP)

Answer 44

an individual born with two recessive alleles for the TAS2R38 gene who experiences little or no taste from the compounds phenylthiocarbamide (PTC) and propylthiouracil (PROP)

Question 45

taster (of PTC/PROP)

Answer 45

an individual born with one or two dominant alleles for the TAS2R38 gene and able to taste the compounds phenylthiocarbamide (PTC) and propylthiouracil (PROP)

Question 46

studies of PROP

Answer 46

- Tasters are more finicky eaters because bitter tastes are more intense to these individuals → tend to dislike foods high in bitter compounds - Taster status is related to body type

Question 47

gene that expresses PTC/PROP receptors

Answer 47

member of the bitter family in TAS2R38

Question 48

cross-modality matching

Answer 48

the ability to match the intensities of sensations that come from different sensory modalities; allows insight into sensory differences

Question 49

removing input from one of the taste nerves can intensify whole-mouth taste sensations

Answer 49

- Because inputs from the different taste nerves inhibit one another in the brain → loss of input from one nerve releases others from inhibition - In some cases, the release of inhibition is greater than the loss of input and the result is intensification of whole-mouth taste - When damage is more widespread, however, taste perception diminishes

Question 50

health consequences of variation in taste sensations

Answer 50

- Variation in the sensory properties of foods and beverages affects food preferences and thus diet - Since diet is a major risk factor for a variety of diseases, genetic variation in taste plays a role in these diseases

Question 51

how taste contributes to the regulation of nutrients

Answer 51

- The taste system responds to a small set of molecules that we encounter in nature - This precise tuning is consistent with the role of taste as a system for detecting nutrients and “antinutrients” - Each of the four basic tastes is responsible for a different nutrient or antinutrient and has evolved according to its purpose

Question 52

purposes of the four basic tastes

Answer 52

- bitter: nature's poison detector - sour: configured to reject any highly acidic solution without identifying its source - salty and sweet: enable us to ingest foods that contain nutrients that our bodies need

Question 53

how flavor contributes to the regulation of nutrients

Answer 53

- When we eat foods, we experience retronasal olfactory stimulation → specific features of the olfactory molecules interact with receptors tuned to them → all receptors of a given type project to individual glomeruli in the olfactory brain → the pattern across the glomeruli creates a “picture” of the chemical structure of a molecule or a mixture of molecules → these pictures are stored in the brain and can be associated with positive or negative affect, depending on the consequences of what we eat - If we get sick, the pictures acquire negative affect - If our brains judge the consequences as good, the pictures acquire positive affect

Question 54

specific hungers theory

Answer 54

the idea that deficiency of a given nutrient produces craving (a specific hunger) for that nutrient - could apply to salty and sweet, but proved wrong for other nutrients

Question 55

sensory-specific satiety

Answer 55

eating a variety of foods presented because one gets bored eating any single food

Question 56

evaluative conditioning

Answer 56

the association of negative or positive affect with a neutral experience

Question 57

labeled lines

Answer 57

a theory of taste coding in which each taste nerve fiber carries a particular taste quality

Question 58

taste adaptation and cross-adaptation

Answer 58

- All sensory systems show adaptation effects, in which constant application of a certain stimulus temporarily weakens subsequent perception of that stimulus - Adaptation to certain components in one food can change the perception of a second food

Question 59

capsaicin

Answer 59

produces the burn associated with chili peppers - stimulates both fibers that mediate warmth and those that mediate burn

Question 60

burn experienced from chili peppers in highly variable across individuals and comes from two sources

Answer 60

- Individuals with the largest number of fungiform papillae (supertasters) have the most fibers mediating oral pain, and thus they perceive the most intense oral burn from chilis - Capsaicin desensitizes pain receptors → thus, individuals who consume chilis quite often are chronically desensitized

Question 61

scoville unit

Answer 61

the number of times you have to dilute the dry pepper until the burn can no longer be detected