Chapter 15: Taste Flashcards
__________ sensation is the sensation of an odor that is perceived when chewing and swallowing force an odorant emitted by the mouth up behind the palate into the nose.
Retronasal olfactory
_________ are structures that give the tongue its bumpy appearance.
Papillae
_______ are slender projections on the tips of some taste bud cells that extend into the taste pore.
Microvilli
Taste vs. Flavor
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.
Flavor: The combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction.
Considered a metasensation
Retronasal Olfactory Sensation:
The sensation of an odor that is perceived when the act of chewing & 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.
Retronasal Olfactory Sensation:
The sensation of an odor that is perceived when the act of chewing & 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.
Flavor
The combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction.
Considered a metasensation
Molecules released into the air inside our mouths as we chew and swallow travel up through the retronasal passage into the nose, then move up and contact the ________ .
olfactory epithelium
Connection between taste & smell:
Brain imaging studies:
Brain processes odors differently, depending on whether they come from nose or mouth.
The food industry adds sugar to intensify the sensation of fruit juice.
Increase in sweetness (a pure taste sensation) increases perceived olfactory sensation of fruit.
Connection between taste & smell:
Brain imaging studies:
Brain processes odors differently, depending on whether they come from nose or mouth.
The food industry adds sugar to intensify the sensation of fruit juice.
Increase in sweetness (a pure taste sensation) increases perceived olfactory sensation of fruit.
Connection between taste & smell:
Brain imaging studies:
Brain processes odors differently, depending on whether they come from nose or mouth.
The food industry adds sugar to intensify the sensation of fruit juice.
Increase in sweetness (a pure taste sensation) increases perceived olfactory sensation of fruit.
Taste buds
Create neural signals conveyed to brain by taste nerves.
Embedded in structures: Papillae (bumps on tongue)
Each taste bud contains taste receptor cells.
Information sent to brain via cranial nerves.
Papillae
bumps on tongue
4 kinds of papillae:
- Filiform papillae:
Small structures on the tongue that provide most of the bumpy appearance.
Have no taste function. - Fungiform papillae:
Mushroom-shaped structures (maximum diameter 1 mm) distributed most densely on the edges of the tongue.
An average of 6 taste buds per papilla buried in the surface. - Foliate papillae:
Folds of tissue containing taste buds.
On rear of the tongue lateral to circumvallate papillae, where the tongue attaches to the mouth. - Circumvallate papillae: Circular structures that form an inverted V on the rear of the tongue.
Mound-like structures surrounded by a trench.
Much larger than fungiform papillae.
Filiform Papillae
Small structures on the tongue that provide most of the bumpy appearance.
Have no taste function.
Fungiform Papillae
Mushroom-shaped structures (maximum diameter 1 mm) distributed most densely on the edges of the tongue.
An average of 6 taste buds per papilla buried in the surface.
Foliate Papillae
Folds of tissue containing taste buds.
On rear of the tongue lateral to circumvallate papillae, where the tongue attaches to the mouth.
Circumvallate Papillae
Circular structures that form an inverted V on the rear of the tongue.
Mound-like structures surrounded by a trench.
Much larger than fungiform papillae.
Neural signals from the taste buds in those papillae are transmitted via cranial nerves _____ to the brain
VII, IX, and X
Neural signals from the taste buds in those papillae are transmitted via cranial nerves _____ to the brain.
VII, IX, and X
Typical variability in the density of fungiform papillae from one individual to the next.
This difference determines the difference between a Supertaster and a Non-Supertaster.
Typical variability in the density of fungiform papillae from one individual to the next.
This difference in density is the difference between a Supertaster and a Non-Supertaster.
What happens when we cannot perceive taste but can still perceive smell?
Patient case: Damaged taste, but normal olfaction—could smell lasagna, but had no flavor
Similar effect created in lab: Chorda tympani anesthetized with lidocaine
Chorda tympani: The branch of cranial nerve VII (the facial nerve) that carries taste information from the anterior, mobile tongue (the part you can stick out)
Chorda tympani
The branch of cranial nerve VII (the facial nerve) that carries taste information from the anterior, mobile tongue (the part you can stick out)
Microvilli
Slender projections on the tips of some taste bud cells that extend into the taste pore.
Contain the sites that bind to taste substances.
Not tiny hairs (as the name implies).
They are extensions of the cell membrane.
Tastant
Any stimulus that can be tasted
Tastants can be divided into 2 large categories:
Some made up of small, charged particles that taste salty or sour.
Small ion channels in microvilli membranes allow some types of charged particles to enter but not others.
Other tastants are perceived via G-protein-coupled receptors (GPCRs) similar to that in the olfactory system.
These molecules taste sweet or bitter.
Tastants made up of small, charged particles taste ….
salty or sour
Small ion channels in microvilli membranes allow some types of charged particles to enter but not others.
Tastants perceived via G-protein-coupled receptors (GPCRs) are….
molecules that taste sweet or bitter
Tastants made up of small, charged particles taste ….
salty or sour
Small ion channels in microvilli membranes allow some types of charged particles to enter but not others.
Tastants perceived via G-protein-coupled receptors (GPCRs) are….
molecules that taste sweet or bitter
Tastants that taste sweet or bitter are detected via _____ .
G-protein-coupled receptors (GPCRs) similar to that in the olfactory system.
Tastants that taste salty or sour are detected via _____ .
Small ion channels in microvilli membranes that allow some types of charged particles to enter but not others.
Taste processing in the CNS:
Pathway
Taste buds to cranial nerves to medulla and thalamus and then to cortex
- Taste buds
- Cranial nerves
- Medulla
- Thalamus
- Cortex
Taste processing in the CNS:
Pathway
Taste buds to cranial nerves to medulla and thalamus and then to cortex
- Taste buds
- Cranial nerves
- Medulla
- Thalamus
- Cortex
Taste processing in the CNS:
Insular Cortex
Primary cortical processing area for taste.
The part of the cortex that first receives taste information.
Taste processing in the CNS:
Pathway
Taste buds to cranial nerves to medulla and thalamus and then to cortex
- Taste buds
- Cranial nerves
- Medulla
- Thalamus
- Cortex
Taste processing in the CNS:
Orbitofrontal Cortex
The part of the frontal lobe of the cortex that lies above the bone (orbit) containing the eyes.
Receives projections from insular cortex.
Involved in processing of temperature, touch, smell, and taste, suggesting it may be an integration area.
Taste information projects from the ____ to the _____, then to the thalamus, then to the _____, and finally to the _____ cortex.
Taste information projects from the tongue to the medulla, then to the thalamus, then to the insula, and finally to the orbitofrontal cortex
Salty Taste
Salt is made up of 2 charged particles:
Cation and anion (e.g. Na+ & Cl-)
Salty tastes are produced by the cation.
The ability to perceive salt is not static.
Low-sodium diets will increase in intensity of salty foods over time.
Liking for saltiness is not static.
Early experiences can modify salt preference.
Chloride-deficiency in childhood leads to increased preference for salty foods later.
Salty tastes are produced by the ____
CATION!!
Sour Taste
Comes from acidic substances.
Relative proportion of H+ ions.
Only liked at low concentrations.
At high concentrations, acids will damage both external & internal body tissues.
Bitter Taste
25 different bitter receptors
Quinine is a prototypically bitter-tasting substance.
Found in tonic water.
Cannot distinguish between tastes of different bitter compounds.
Many bitter substances are poisonous.
Ability to “turn off” bitter sensations—beneficial to liking certain vegetables.
Bitter sensitivity is affected by hormone levels in women, intensifies during pregnancy
Quinine
a prototypically bitter-tasting substance.
Found in tonic water
Sweet Taste
Evoked by sugars
Many different sugars that taste sweet:
Glucose: Principle source of energy for most animals.
Fructose: Sweeter than glucose.
Sucrose: Common table sugar. Combination of glucose & fructose.
Single receptor responsible for all sweet perception.
Different sweeteners stimulate different parts of receptor.
Artificial sweeteners stimulate this receptor as well.
Structure of the T1R2-T1R3 heterodimer sweet receptor, showing binding sites for both large and small sweet molecules.
….
Survival value of taste
Taste is a system for detecting nutrients and antinutrients.
Bitter: Might signal poisons
Sour: Configured to detect acidic solutions that might harm the body
Sweet & Salty: Our bodies need sodium and sugar to survive
Survival value of taste
Taste is a system for detecting nutrients and antinutrients.
Bitter: Might signal poisons
Sour: Configured to detect acidic solutions that might harm the body
Sweet & Salty: Our bodies need sodium and sugar to survive
The tastes that human subjects perceive for each of four stimuli
sweet & bitter are most easily picked out.
In our evolutionary past, specific hungers for sugar and salt were adaptive
The tastes that human subjects perceive for each of four stimuli
sweet & bitter are most consistently correctly, easily picked out.
In our evolutionary past, specific hungers for sugar and salt were adaptive
The Pleasures of Taste
Babies
Infants’ behavior and facial expressions reveal innate preferences for certain foods.
Different flavored foods placed on tips of infants’ tongues:
Sweet food evokes a “smilelike” expression followed by sucking
Sour produced pursing and protrusion of lips
Bitter produced gaping, movements of spitting, and sometimes vomiting movements
The Pleasures of Taste
Babies
Infants’ behavior and facial expressions reveal innate preferences for certain foods.
Different flavored foods placed on tips of infants’ tongues:
Sweet food evokes a “smilelike” expression followed by sucking.
Sour produced pursing and protrusion of lips.
Bitter produced gaping, movements of spitting, and sometimes vomiting movements.
The Pleasures of Taste:
Babies
Infants’ behavior and facial expressions reveal innate preferences for certain foods.
Different flavored foods placed on tips of infants’ tongues:
Sweet food evokes a “smilelike” expression followed by sucking.
Sour produced pursing and protrusion of lips.
Bitter produced gaping, movements of spitting, and sometimes vomiting movements.
Specific hungers theory
The idea that deficiency of a given nutrient produces craving for that nutrient
Cravings for salty or for sweet are associated with deficiencies in those substances.
However, the theory has not been supported for other nutrients, such as vitamins.
Theory only holds for sweet and salty foods.
The special case of umami:
Candidate for 5th basic taste
Comes from monosodium glutamate (MSG)
Glutamate: Important neurotransmitter
Safety issues in human consumption:
Can lead to numbness, headache, flushing, tingling, seating, and tightness in the chest if sensitive individuals consume a large amount
For most people, MSG does not pose a problem in small doses
The special case of fat
Like protein, fat is an important nutrient
Fat molecules evoke tactile sensations like oily, viscous, creamy, etc.
Rats have fatty acid receptors on their tongues, and humans may too.
Digesting fat in the gut produces conditioned preferences for the sensory properties of the food containing fat.
The special case of umami:
Candidate for 5th basic taste
Comes from monosodium glutamate (MSG)
Glutamate: Important neurotransmitter
Safety issues in human consumption:
Can lead to numbness, headache, flushing, tingling, seating, and tightness in the chest if sensitive individuals consume a large amount
For most people, MSG does not pose a problem in small doses
The special case of fat
Like protein, fat is an important nutrient
Fat molecules evoke tactile sensations like oily, viscous, creamy, etc.
Rats have fatty acid receptors on their tongues, and humans may too.
Digesting fat in the gut produces conditioned preferences for the sensory properties of the food containing fat.
Taste adaptation and cross-adaptation:
All sensory systems show adaptation effects.
Constant application of certain stimulus temporarily weakens subsequent perception
Example:
Adaptation to salt in saliva affects our ability to taste salt.
Cross-adaptation:
When the taste of one food affects the taste of another.
Example: A sour beverage tastes too sour after eating a sweet substance.
Taste adaptation and cross-adaptation:
All sensory systems show adaptation effects.
Constant application of certain stimulus temporarily weakens subsequent perception.
Example:
Adaptation to salt in saliva affects our ability to taste salt.
Cross-adaptation:
When the taste of one food affects the taste of another.
Example: A sour beverage tastes too sour after eating a sweet substance.
Cross-adaptation
When the taste of one food affects the taste of another.
Example: A sour beverage tastes too sour after eating a sweet substance
Taste adaptation and cross-adaptation:
All sensory systems show adaptation effects.
Constant application of certain stimulus temporarily weakens subsequent perception.
Example:
Adaptation to salt in saliva affects our ability to taste salt.
Cross-adaptation:
When the taste of one food affects the taste of another.
Example: A sour beverage tastes too sour after eating a sweet substance.
Genetic Variation in Taste Experience
Arthur Fox (1931) discovered that phenylthiocarbamide (PTC) tastes dramatically different to different people Bitter taste to some but not to others.
1960s: Started using propylthioracil (PROP) instead of PTC because it’s safer.
Gene for PTC/PROP receptors discovered in 2003.
Individuals with 2 recessive genes are nontasters of PTC/PROP.
Individuals with one or more of the genes are tasters of PTC/PROP.
Supertaster
Individual who is a taster of PTC/PROP and has a high density of fungiform papillae.
Perceives the most intense taste sensations.
Genetic Variation in Taste Experience:
PTC/PROP
Arthur Fox (1931) discovered that phenylthiocarbamide (PTC) tastes dramatically different to different people Bitter taste to some but not to others.
1960s: Started using propylthioracil (PROP) instead of PTC because it’s safer.
Gene for PTC/PROP receptors discovered in 2003.
Individuals with 2 recessive genes are nontasters of PTC/PROP.
Individuals with one or more of the genes are tasters of PTC/PROP.
Cross-modality matching
Ability to match the intensities of sensations that come from different sensory modalities.
Used to assess intensity of taste sensations for nontasters, medium tasters, and supertasters.
Nontasters match the bitterness of PROP to the same intensity as the sound of a watch or a whisper.
Medium tasters match the bitterness of PROP to the same intensity as the smell of frying bacon or the pain of a mild headache.
Supertasters match the bitterness of PROP to the same intensity as the brightness of the sun or most intense pain ever experienced
Cross-modality matching
Ability to match the intensities of sensations that come from different sensory modalities.
Used to assess intensity of taste sensations for nontasters, medium tasters, and supertasters.
Nontasters match the bitterness of PROP to the same intensity as the sound of a watch or a whisper.
Medium tasters match the bitterness of PROP to the same intensity as the smell of frying bacon or the pain of a mild headache.
Supertasters match the bitterness of PROP to the same intensity as the brightness of the sun or most intense pain ever experienced.
Health consequences of taste sensation
Variations in sensory properties of foods & beverages affects food preferences and therefore diet.
For instance, some vegetables have a bitter taste and thus might be avoided by supertasters.
Valerie Duffy and colleagues showed that among men getting routine colonoscopies, those tasting PROP as the most bitter had the most colon polyps.
Note that fats also taste bitter to supertasters, so this may cause them to eat fewer high-fat foods, which could lower their risk for heart disease.
Pleasure and retronasal versus orthonasal olfaction
Orthonasal olfaction: Olfaction through the nostrils.
Do we learn to like or dislike smells separately for retronasal versus orthonasal olfaction? Possibly.
Example: Many people like the smell of freshly cut grass, but wouldn’t want to eat it.
However, if an aversion is acquired retronasally, it usually shows up orthonasally as well.
Example: Becoming sick from eating fish and then disliking even the smell of fish.
Orthonasal olfaction
Olfaction through the nostrils
Chili Peppers
Acquisition of chili pepper preference depends on social influences
Restriction of liking to humans
Variability across individuals, depending on number of papillae
Capsaicin: The chemical that produces the burn in chilis. Desensitizes pain receptors
Desensitization:
If a food is too hot for your palate, wait for burn to subside after the first mouthful. Your palate will desensitize (from the capsaicin) and you should be able to eat again
Capsaicin
The chemical that produces the burn in chilis.
Desensitizes pain receptors.
Chili Peppers
Acquisition of chili pepper preference depends on social influences.
Restriction of liking to humans.
Variability across individuals, depending on number of papillae.
Capsaicin: The chemical that produces the burn in chilis.
Desensitizes pain receptors
Desensitization:
If a food is too hot for your palate, wait for burn to subside after the first mouthful. Your palate will desensitize (from the capsaicin), and you should be able to eat again
Capsaicin
The chemical that produces the burn in chili peppers.
Desensitizes pain receptors.
Capsaicin Desensitization
If a food is too hot for your palate, wait for burn to subside after the first mouthful. Your palate will desensitize (from the capsaicin) and you should be able to eat again.
Adenosine Monophosphate (AMP)
Natural bitter inhibiter
Found in breast milk
