Midterm 2 - 2E03 Handmade

What are the 4 basic tastes?

sweet, salty, sour and bitter

Papillae

mound of tissue on the tongue, roof and back of mouth, within which taste buds are embedded

Taste bud

Clusters of taste receptor cells found in the walls and grooves of papillae

How many taste receptor cell per taste bud?

There are 50-150 specialized receptor cells within each taste bud

Why do taste buds have microvilli

To increase the surface area for interaction with tastants

Taste receptor cells

specialized epithelial cells (not neurons) with polarized endings. The apical end binds tastants, and the basal end sends signals

Type I taste receptor cells (function and how many)

glial-like function (housekeeping), and maybe salty taste

50% of the cells in a taste bud

Type II taste receptor cells (function and how many)

Involved in the detection of sweet, umami, and bitter tastes through GPCR

Approximately 30% of the cells in a taste bud.

Do type II taste receptors synapse on afferent fibres?

No, they don’t make synapses with afferent fibres. Instead, type 2 cells release ATP, which acts on adjacent cells or nerve fibres to produce neural signals

Type III taste receptor cells (function and how many)

Responsible for detecting sour taste.

2-20% of the cells in a tastebud

Do type III taste receptors synapse on afferent fibres?

Yes, they form synapses with afferent nerve fibers thorugh chemical synapses with synaptic vessles

Which tastes are mediate through ion channels?

salty and sour

Which tastes are mediated through GPCR?

bitter and sweet

How does sour ion channel receptor work?

either, H+ enters through an ion channel or undissociated organic acids permeate the membrane, dissociate into acid +base, increases acidity of intracellular fluid and closes a K+ channel (depolarization)

Are T2R-bitter receptors monomers, dimers or heterodimers?

May function as monomers or dimers

What are the ligands for bitter receptors?

chemicals, especially those in the nitrogen containing alkaloids (e.g. quinine)

4 examples of bitter ligands?

PROP, quinine, thiamine, PTC

What are the receptor names for GPCR for tastants?

T2Rs (type 2 receptors) for bitter taste and T1Rs for sweet

Are T1R-sweet receptors monomers, dimers or heterodimers?

They function as heterodimers - both T1R2 and T1R3 are required

What are some examples of sweet ligands?

Ligands include sugars (e.g. glucose, fructose, sucrose, aspartame)

Describe the signal cascade of taste transduction, from binding to synaptic cleft

When tastants bind to GPCRs, they activate a G-protein, which then triggers a cascade of intracellular events (Na, K+ and Ca2+ channels). This results in the release of serotonin at the synaptic cleft, transmitting taste information to the brain.

Why type of neuron are afferent taste neurons?

pseudo-unipolar

What 3 cranial nerves carry taste info to the brain?

VII (facial), IX (glossopharyngeal) and X (vagus)

regional coding / chemotopic organization

All tastes can be detected over the entire surface of the tongue but different regions have slightly different thresholds for various tastes

Is taste encoded by labeled-line coding or cross-fibre coding?

Taste coding shows features of roughly labeled lines and cross fibre (combinatorial) coding = responses of a large number of broadly tuned neurons specify properties of a stimulus

Which type of taste receptor cells are generalists?

Type III

Which type of taste receptor cells are specialists?

type II

Is taste ipsilateral or contralateral

taste projects ipsilaterally – doesn’t cross over

Where is the primary gustatory cortex?

in the frontal lobe, within the sylvian fissure = insula and surrounding areas

Is there a gustotopic map?

kind of a taste map but pretty complex, not exactly four distinct quadrants

Where is the secondary gustatory cortex?

Orbitofrontal cortex

What does the secondary gustatory cortex do?

Processes higher aspects of taste functions, such as motivational effects of hunger and satiety (hippocampus) and how good you think food looks (amygdala)

How does the sweet receptor work?

Ligand binding activates the receptor, which activates a G-protein signaling pathway, which ultimately increases CA2+ in the intracellular fluid

Difference between T1R2 and T1R3

small molecules bind to T1R2, large bind to T1R3

What is the difference between taste and flavour?

Taste refers to the five basic sensations detected by our taste buds (sweet, sour, salty, bitter), while flavor is the overall sensory experience, encompassing taste, retronasal olfaction, and other factors like texture and temperatur

Why is it important to taste salt?

Na+ is important to maintain nerve and muscle function (consider the action potential)

Why is it important to taste bitter?

We avoid bitter compounds because they often signal poison/toxicity

How many bitter receptors vs compounds?

thousands of bitter molecules detected by 25 bitter receptors = combinatorial coding

Why is it important to taste sour?

At high concentrations, acids will damage external and internal body tissues

Why is it important to taste sweet?

sugar is the principal energy source for humans, but we don’t need to distinguish many types - only T1R2 and T1R3

Why is taste important?

Each of the 4 basic tastes is responsible for a certain nutrient (sodium, sugar) or antinutrient (acid, poison)

How do we know that taste affective experince and reflexive response are innate

Infants show stereotyped facial expression

Even infants with ancephaly, who lack the prefrontal (primary taste) cortex, still exhibit typical facial expression

How do we decide what is a basic taste? 3

1. Are receptors for the chemicals found in the mouth

2. Does activating those receptors lead to distinct sensations?

3. Is affect hardwired?

Why should/shouldn’t umami and fat be a basic taste

Support:

there are receptors in the mouth that appear to regulate the palatability of protein and fat (e.g. the umami receptor is a heterodimer made up of TAS1R and TAS1R3)

Against:

Proteins and fats are big molecules = they are mostly broken down by the process of digestion

There are receptors for amino acids and fats throughout the gut that don’t contribute to taste

Umami and fat are not universally liked/disliked (i.e. no hardwired affect)

Conscious sensations about fats are evoked by the somatosensory system (e.g. oily, creamy)

How does miraculin work?

Once pH becomes acidic, change in conformation of protein that allows carb part of miraculin to bind to taste receptor and activate it

Can also bind to sweet receptors at neutral pH, blocking natural sweeteners, but doesn’t activate until pH is acidic

supertaster

an individual whose perception of taste sensations is the most intense, due to intensity of fungiform papillae and genetics

How many fungiform papillae per 6mm diameter?

between 5-60, above 30 is considered a supertaster

Specific hungers theory

Missing nutrients are craved

debunked

How do taste preferences develop?

innate preferences (salt, sugar) + learned olfactory effect (from past consequences) = conditioned preferences and aversions

What are the two perceptual aspects of taste?

Taste quality (how sweet, salty, bitter, sour) and taste intensity

Electrogustometry

Deliver small electric current through an electrode or metal disk to a specific point on the tongue or oral cavity

Chemogustometry

Determine threshold bythe concentration at which you can correctly identify/distinguish the sugar water from plain water

Benefits and disadvantages of electrogustometry

More naturalistic

BUT may encounter problems with lingering taste / adaptation

Unable to look at discrete locations

Benefits and disadvantages of electrogustometry

Stimulus application is highly discrete in space and time

BUT

May not accurately represent tastants; thought to be more effective for ion tastants salty and sour

Cannot identify problems that alter taste perception like tasting sweet things as sour, good as bad etc

Ageusia

Total loss of taste, by injury to gustatory nerves or medications (e.g. cancer, depression)

Hypogeusia

A reduction in taste sensitivity, caused by dry mouth, smoking, or illness (e.g. flu, diabetes)

Dysgeusia

taste perceptions are distorted (e.g. sweet becomes salty, metallic taste for cancer patients)

Order taste detection thresholds from lowest to highest. Why are they in this order

Bitter < sour < salty < sweet

We don’t want to accidentally eat poison, or harm tissue with excessive acid so those are lowest

sweet is highest because we don’t really care if we accidentaly eat sweet

Taste is the (most/least) sensitive sensory function

LEAST sensitive, as it as the largest Weber fraction

How are taste detection thresholds affected by age?

Receptor turnover slows with aging, detection thresholds increase

Mixture suppression / masking

When one taste quality suppresses another

E.g. the sugar in tonic water makes it taste less bitter

Adding salt to food reduces perception of bitterness

Why don’t we adapt to food taste?

Usually eating the food doesn’t stay in mouth so stimulus is not entirely constant so you still taste successive bites

Difference between PTC/PROP tasters and non-taster

Tasters have 1-2 versions of the dominant TAS2R38 gene

Nontasters have 2 versions of the recessive TAS2R38 gene

What gene encodes the bitter receptors that PTC and PROP bind to?

TAS2R38 gene

Sound (physics)

Vibrational disturbance of a medium

Sound (psychology)

a physical event that must be converted into a biological signal to produces the perceptual experience of hearing

Vibrational properties of objects

Objects must have inertia and elasticity to vibrate

Fourier analysis

Decomposition of a complex waveform into a series of sine-wave patterns (without prior knowledge of constituent patterns)

What does a fourier spectrum show

How much energy, or amplitude, is present at multiple frequencies

What do complex aperiodic sounds sound like?

Noise - random vibrations

White noise

noise containing all of the frequencies within a particular range

Complex periodic sounds

occurs when the pattern of pressure change repeats itself over regular intervals over time

dB SPL

SPL = sound pressure level

dB SPL indicates that the lowest audible sound was used as a reference

What does a negative dB value mean?

sound quieter than minimum audible level

Equation for decibels

dB = 20 log (p/p0)

decibel (definition)

ratio between sound pressures on a log scale, typically wrt SPL

What is the range of frequencies that (young, healthy) humans can hear

between 20 to 20,000 Hz

Perceptual quality of frequency

pitch

Perceptual quality of amplitude

loudness

Amplitude

The pressure change form peak to peak

Pure tone

Characterized by single sinusoidal function (simplest sound wave)

Sound

A travelling wave of pressure disturbance within a medium

Impact of sound source on a medium

Initial tuning fork displacement crowds neighbouring air molecules = compression

Movement of fork in opposite direction causes air molecules to relax = rarefaction

Nearby air particles acts as vibrators that collide with neighbouring particles and cause them to vibrate

Harmonic series

The fundamental frequency is the lowest frequency component of the sound; all other harmonics are integer multiples of the fundamental

first harmonic = fundamental frequency = 100 Hz

second harmonic = f0 × 2 = 100×2 = 200Hz

third harmonic = f0 × 3 =100× 3 = 300 Hz

What is the value of p0 in Pascals

0.00002 Pa or 20uPa

Purpose of auditory system

o Finding mates – e.g. songbirds

o Avoiding predators, danger

o Communication

o Finding food

o For pleasure

o Distant and fastest sense

Umami

protein, specifically the amino acid L-glutamate, savouriness

Fat

fatty acids

Umami receptor

heterodimer of TAS1R and TAS1R3

Surface area of a sphere equation

surface area 4 pi r²

Inverse square law equation

Intensity = 1/r²

Significance of inverse square law

intensity decreases exponentially vs distnace

External auditory canal

Channels sound to the eardrum

Pinna

Funnels sound with bumps and grooves

Tympanic membrane

eardrum; sound waves cause it to vibrate, elastic membrane that seals off the EAC

Auditory ossicles

tiny bones that conduct vibration of the eardrum to the inner ear

Malleus

first, largest ossicle

Incus

Second/middle ossicle

Stapes

Third, smallest ossicle

Footplate connects with oval window