Chapter 15: Gustation Flashcards
Gustation
Assesses quality of material entering system
- Basic tastes
Basic tastes
5 well-established taste categories- sweet, salty, umami, sour, and bitter
Nutritive tastes
Sweet, salty, and umami
Non-nutritive tastes
Sour and bitter
Flavor perception
More complex and multidimensional than taste perception
Tastants
Molecules that taste receptors “recognize” and respond to by producing neural signals that brain represents as perception of different tastes
Flavor
total sensory experience evoked by ingesting something
- includes perception of basic tastes, perception of basic tastes, perception of other attributes of tastants, such as pleasantness and intensity, and other sensory properties, most importantly smell
Affected by many things other than taste
*olfaction, hunger/thirst, vision, audition, and mouth feeling
Taste and Flavor
- Sweet- sucrose, fructose, glucose
- Salty- NaCl, KCl, LiCl
- Umami- monosodium glutamate, L-arginine, L-glutamine
- signals presence of protein in food - Bitter- quinine, caffeine, PROP
- Sour- citric acid, acetic acid, hydrochloric acid
Trigeminal Sense
Sense that signals presence of irritants in mouth, such as menthol and chili pepper
- contributes to “mouth feel” of foods
Taste buds
Structures that contain taste receptor cells, within papillae in mouth
Perceiving Tastes and Flavors
Taste buds and taste receptor cells (TRCs)
Anatomical and neural basis of taste and flavor perception
On tongue, taste buds are found in three of the four types of papillae
- fungiform, folliate and circumvallate
- filiform do not contain taste buds
Fungiform papillae
Tiny mushroom- shaped structure located along edges and top of front two-thirds of tongue
- 3-5 taste buds on upper surface
Folliate papillae
Ridgelike folds of tissue located on sides of tongue neat the back
- few hundred taste buds are tucked into each fold
Circumvallate papillae
Larger mushroom- shaped structures situated in row at back of tongue
- contains 200- 700 taste buds around its side
Filiform
Manipulate food on tongue
1/3 of taste buds are found on […]
1/3 of taste buds are found on soft palate, epiglottis, and upper esophagus
Free nerve endings
Trigeminal nerve- how something feels in mouth (non-taste) factors
We have […] taste buds each of which have […] taste receptor cells
We have 3000-12000 taste buds each of which have 40000-100000 taste receptor cells
Taste receptors cells (TRCs)
Elongated neurons, packed within taste buds, that transduce tastants into neural signals
- TRCs only live about 1 week
- New TRCs developed from basal cells in taste buds - Cilia of TRCs project into taste pore at top of taste bud, when cilia come into contact with tastants molecules dissolved in saliva
There are two types of TRCs
Receptor cells
Presynaptic cells
Receptor cells
Type of taste receptor cells containing receptors that initiate transduction of sweet, umami, and bitter tastants
- do not have synapses with cranial nerve fibers, GPCRs
Presynaptic cells
Type of receptor cells in which receptors take form of ion channels where transduction of salty and sour tastants is initiated
GPCRs involved in taste perception
Characterized biochemically and genetically
- Linked via behavioral and genetic studies in mice to the transduction of sweet, umami, and bitter tastants
- T1R2-T1R3: sweet tastants
- T1R1-T1R3: umami tastants
- T2Rs bitter tastants - Acids Sour tastant
- ENaC Salty (everyday and other salts categories)
- KO: transduction of Na+ ions in relatively low concentrations
Cell-to-Cell signaling
In taste perception, signals from receptor cells to presynaptic cells cause the presynaptic cells to release neurotransmitters in a way that carries information about sweet, umami, and bitter tastants
- ion channels in presynaptic cells transduce salty and sour tastants
Taste perception models
Labeled-line pattern
Across- fiber pattern
Labeled-Line Pattern
Suggests cranial nerve fibers are responsible for information about only one taste
- cortical neurons on receiving end of these signals also response only to information about signal type of tastants
Across-fiber pattern
Suggests cranial nerve fibers are responsible for information from several tastes; evidence supports the across-fiber pattern model
- cortical neurons receiving these signals are broadly tuned to respond to signals carrying information about multiple types of tastants
Receptor Cells and Presynaptic cells
Receptor cells: cilium of sweet, umami, and bitter receptor cells contain receptors
Presynaptic cell: cilium of cells with salty and sour ion channels
Across- fiber pattern model: […] carry signals to the brain
Across- fiber pattern model: cranial nerves carry signals to the brain
- VII (facial; front two-thirds of tongue and soft palate)
- IX (glossopharyngeal; back third of tongue)
- X (vagus; epiglottis, and upper esophagus)
Cranial nerve send signals to:
Nucleus of solitary tract (gustatory nucleus) —> Ventral posterior medial nucleus of thalamus —> primary taste cortex (representation of taste quality)
Primary taste cortex
First cortical areas to receive taste signals (representation of taste quality)
- anterior insular cortex
- frontal operculum
Goes to amygdala (representation of emotion), orbitofrontal cortex (representation of reward value of food), hypothalamus (representation of hunger)
Taste Quality versus Reward Value
Taste quality- constant firing rate in primary taste cortex
Reward Value- decreasing firing rate in OFC
Adaptation
Tastants from one basic taste doesn’t reduce sensitivity to other basic tastes
Cross- Adaptation
Cross- adaptation between similar tastants can occur
Expectations and Flavor Perception
Increases price= increased pleasure
- difference seen in orbitofrontal cortex
Cognitive Influences in the OFC, and the Flavor of Expensive Wine
Expectations about a food or drink can influence activity in parts of the brain involved in signaling flavor- expectations can truly change the flavor that you perceive
Satiety
Reduction in appetite for food
Sensory- Specific Satiety
Reduction in appetite specifically for foods that have been recently consumed
- aids in avoidance of nutritional deficiencies associated with a limited diet
- may be influence by memory and previously consumed food
Regulated food intake without taste information
KO mice still preferred sucrose water over sucralose water because of the nutritious values of sugar water
Individual Differences in Taste and Flavor Perception
Ability or inability to taste certain bitter substances (most common)
- two gene version: PAV (75%) and AVI (25%)
Ability to taste bitter and other substances more intensely
- Taster - Nontaster - Supertaster
Taster
People with form of gene that allows them to detect certain bitter tastants
Nontasters
People with form of gene that allows them to detect certain bitter tastants only at very high concentrations
Supertasters
Tasters who have about 2x as many fungiform papillae as others and are especially sensitive to certain bitter tastants
- 1/3 of tasters are supertasters
Individual Difference in Taste and Flavor Perception
Many factors may lead to individual difference in taste preferences
- Chocolate
- Capsaicinoids: increased capsaicin conc= increased perceived spiciness
The taste and use of artificial sweeteners
Artificial sweeteners create the perception of sweetness in the absence of sucrose by binding to the T1R3 GPCR, just like sucrose does
Brain responses to artificial sweeteners: Behavioral responses research
- measurable effect on overt behavior associated with difference between natural and artificial sweeteners
- perceptual system assessment takes the body’s current capabilities into account (ex. Assessing features of the spatial environment)
Brain activity in response to sweeteners
Activity in response to sucrose: anterior insular cortex, frontal operculum, and orbitofrontal cortex= increase activation
*same activation doesn’t occur in sucralose
Behavioral Responses to Artificial Sweeteners
Weight Loss
- artificial sweeteners might not effectively facilitate weight loss - artificial sweeteners can have complex behavioral effects - more research is needed
