Chapter 15: Taste

cross-adaptation

when the taste of one food affects the taste of another

Explain retronasal olfaction, what is it good for?

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

If the hydrogen content of a tastant increases, what taste will we perceive?

-Bitter?

What do we know about the genetics of taste ability? What are pseudogenes?

- Cross Modality Matching: Ability to match intensities of sensations that come from different sensory modalities (used to assess intensity of taste sensations for nontasters, medium tasters, and supertasters) -variations in sensory properties of foods and beverages affects food preferences and therefore diet -men that taste 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 higher-fat foods, which lowers their risk for heart disease (why supertasters tend to be leaner) - Pseudogens: non- functional genes

How are a nontaster and a supertaster's tongue different? And, how does this affect their experience of taste?

-Nontasters: individuals with two recessive genes -Supertaster: individual who is a taster of PTC/PROP and has a high density of fungiform papillae. -Supertasters perceives the most intense sensations.

taste adaptation

-all sensory systems show adaptation effects -constant application of certain stimulus temporarily weakens subsequent perception

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 ( so the " bud" is not the receptor cell, it's just the structure containing the cell). - information is sent brain via cranial nerves

facial expressions and taste

-infants behavior and facial expressions reveal innate preferences for certain foods -different flavored foods placed on tips of infants tongues: 1. sweet evokes a "smilelike" expression followed by sucking 2. sour produced pursing and protrusion of lips 3. bitter produced gaping, movements of spitting and sometimes vomiting movements

too little salt causes

-muscles won't contract -blood won't circulate -neurons won't fire -food won't digest -wounds won't heal -fluids won't be regulated -the liver won't clear waste products

do we learn to like or dislike smells separately for retronasal vs orthonasal olfaction (olfaction through the nostrils)

-possibly Ex: 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 shouws up orthonasally as well Ex: becoming sick from eating gish and then disliking the smell of fish as well

bitter

-quinine: prototypically bitter-tasting substance, used to be used to treat malaria -can't distinguish between tastes of different bitter compounds (we react the same to all of them) -many bitter substances are poisonous -ability to "turn off" bitter sensations: beneficial to liking certain veggies -bitter sensitivity is affected by hormone levels in women, intensifies during pregnancy

artificial sweeteners

-stimulates the same receptor which in turn produces the same signal to the brain -artificial sweeteners like saccharin and aspartame don't taste like sugar -some claim produce additional tastes such as bitterness as well as sweet (prob due to genetic differences) -people use these to lose weight but there is evidence that actually leads to an increase in weight -the uncoupling of sensory properties of these diet food form their metabolic consequences disrupts regulation leading to weight gain

survival value of taste

-taste is a system for detecting nutrients and anti-nutrients bitter: might signal poisons sour: configured to detect acidic solutions that might harm body sweet and salty: our bodies need sodium and sugar to survive. we are mostly seawater inside

too much salt causes

-tissues will swell (feet) -enlarged heart, increased blood pressure -effects listed for too little salt will shut down -14 teaspoons will make you real sick, 40 teaspoons will kill you

connection between taste and smell

Brain imaging studies: brain processes odors differently, depending on whether they come from nose or mouth Food industry: adds sugar to intensify sensation of fruit juice -increase in sweetness (pure taste sensation) increased perceived olfactory sensation of fruit

What gives the tongue its bumpy appearance?

Filiform Papillae: -small structures on the tongue and have no taste function

If you damaged or anesthetized the chorda tympani, how would taste be effected?

If damaged you would lose your sense of taste but could smell still -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)

How do neurotransmitters affect our perception of certain foods?

Learned Aversion: avoidance of a novel flavor after it has been paired with gastric illness. the smell, not the taste of the substance is key

What is the role of the insular cortex and taste?

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

What are the four basic tastes?

Sweet, Sour, Salty, Bitter

Filiform papillae, on humans are pretty worthless, why? But on cats, they are quite important and shaped differently. Explain.

The Filaform papillae on a cat has hooks this is to help the cat self groom as well as hold food or struggle with prey as well as licking meat off the bone.

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 and you should be able to eat the rest of your meal

How could you easily identify circumvallate papillae?

The circumvallate papillae are circular structures that form an inverted V on the rear of the tongue. -3-5 on each side -moundlike structures surrounded by a trench -Much larger than fungiform papillae.

What's the role of the orbitofrontal cortex and taste?

The part of the frontal lobe of the cortex that lies above the bone (orbit) containing the eyes. - receives projections from the insular cortex -involved in processing of temperature, touch, smell and taste, suggesting it maybe be a key integration area for all the senses.

Explain the theory of "labeled lines".

Theory of taste coding in which each taste fiber carries a particular taste quality. -major source of controversy in lit other possibility: patterns of activity across many different taste neurons Examples of both types of coding in other senses: -color vision and olfaction use pattern coding -hearing uses labeled-line approach (think place theory)

what is the role of inhibition

an important role in processing taste information in the brain. the brain is sending inhibitory messages to the mouth as it's receiving taste and body sensation from the mouth function: to protect our whole mouth perception of taste when we have injuries to taste system. Descending inhibition from taste cortex blocks pain perception survival value b/c we need to eat even if our mouth has been injured

tastant

any stimulus that can be tasted -can be divided into 2 large categories: 1. some are 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 2. other tastants are perceived via G protein-coupled receptors (GPCRs) similar to that in the olfactory system. these molecules taste sweet or bitter

Scientists use the chemical PROP for what?

arthur Fox discovered that phenylthiocarbamide (PTC) tastes dramatically different to different people -bitter taste to some but not to others -Scientist starting using propylthioracil (PROP) instead of PTC because it is safer. -gene for PTC/PROP receptors discovered in 2003: individuals with 2 recessive genes are nontasters of PTC/PROP and individuals with one or more of the genes are tasters of PTC/PROP

sour

comes from acidic substances -at high concentrations, acids will damage both external and internal body tissues

sweet

evoked by sugars -many different sugars that taste sweet: 1. glucose: principle source of energy for most animals 2. fructose: even sweeter than glucose (corn syrup below) 3. sucrose: common table sugar and combination of glucose and fructose -single receptor responsible for all sweet perception: 1. different sweeteners stimulate different parts of receptor 2. artificial sweeteners stimulates this receptor as well

What is the foliate papillae

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

taste buds and taste receptor cells

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: we now know they are extensions of the cell membrane

what is the fungiform papillae

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

What is umami and why is science reluctant to state it as a fifth taste? What is its connection to MSG?

savory "meaty" taste. -candidate for fifth basic taste -contains glutamate which is an important neurotransmitter. -Umami activated MSG which is a flavor enhancer used to be used in chinese food -safety issues in human consumption: can lead to "chinese restaurant syndrome- numbness, headache, flushing, tingling, seating, tightness in the chest if sensitive individuals consume a large amount -for most people, msg doesn't pose a problem in small doses -controversial b/c many people don't have detectors for this taste

why can't we drink sea water

sea water= 3.5% salt; human blood= 0.9% the concentration of salt outside the cells is higher than that inside so water comes out of your cells to dilute the salt. however, your cells need this water and become dehydrated. on a larger scale, your kidneys pull in water from the rest of your body to dilute the salt and you pee it out but also lose a lot of fresh water in the process so you get dehydrated and begin dying even as you become thirstier.

What is the basic evolutionary or survival purpose of our gustatory sense?

specific hungers theory: the idea that deficiency of a given nutrient produces craving ( a specific hunger for 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

If we can't taste fat (with our taste buds) how can we perceive it

supertasters perceive it as bitter

where is the pathway when it comes to taste processing

taste buds to cranial nerves to medulla and thalamus and then on to the cortex

salt is extremely important because

the body needs it but cannot make manufacture it on its own. salt is made up of 2 charged particles: a cation Sodium which is a metal with a + charge and the anion Chloride which is a poisonous gas with a - charge 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 and gestational experiences may affect liking for saltiness

What accounts for flavor?

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

we know that taste goes to an area of the brain called...

the insular cortex (sort of tucked underneath the frontal cortex) but much of it's neural working remains a mystery -also mixed in with taste pathways are other somatosensory nerves which deliver mouth sensations such as pain, burning and texture