Lecture 24 - Taste

Question 1

Gustation

Answer 1

taste

Question 2

Olfaction

Answer 2

smell

Question 3

What is the stimulus?

Answer 3

The sensations of taste and smell arise in response to contact with chemicals in the environment, either that we put in our mouth (tastes), or that we inhale (odours)
The cells that detect these stimuli, therefore, are chemoreceptors (sensors able to detect chemicals)

Question 4

What do the chemical senses do?

Answer 4

Allow us to detect chemicals in the environment that might help us survive and fulfill our biological destiny!
Information of taste and smell goes to very primitive part of the brain which triggers emotional responses and behaviours

Finding food and avoiding poisons
Finding a compatible mate (once sexual maturity has been reached)

Question 5

taste buds in

Answer 5

tongue papillae

Question 6

taste buds in the tongue papillae

Answer 6

Bumps and within these papillae are things called taste pores and taste buds are within the taste pores
Present food to a variety of chemoreceptors in our mouth to determine in the first instance whether it is something we should spit out
Natural instinct is that bitter things could be posionous so usually spit it out
Folds of epithelium that lines the sides of our tongue are called the foliate papillae
Even further back there are larger bumps - vallate papillae

Taste pores
Little holes around the outside of papillae
Coming out of these pores are little hairs called microvilli which assess the environment in your mouths at that time
Also in these pores are taste buds which are where our chemoreceptors are located

Taste bud
Also have taste bids on palate (roof of mouth) , pharynx (back of throat) and epiglottis

Question 7

Taste pores

Answer 7

Little holes around the outside of papillae
Coming out of these pores are little hairs called microvilli which assess the environment in your mouths at that time
Also in these pores are taste buds which are where our chemoreceptors are located

Question 8

Humans can detect how many different tastes

Answer 8

5

Question 9

Different tastes

Answer 9

Sweet 
Sour
Salty 
Umami 
Bitter

Question 10

Sweet

Answer 10

Sweet – stimulated by sugars
e.g. fructose
Also stimulated by artificial sugars

Question 11

Sour

Answer 11

Sour – stimulated by acids

e.g. acetic acids

Question 12

Salty

Answer 12

Salty – stimulated by sodium (NaCl)

Question 13

Bitter

Answer 13

Bitter – complex, but typically stimulated by alkaloids

Learnt to regard them as palatable rather than regard them as dangerous, habituation

Question 14

Umami

Answer 14

Umami – stimulated by amino acids, especially glutamate

E,g, MSG - glutamate stimulates our umami receptors

Question 15

Taste buds

Answer 15

2000-5000 taste buds, on tongue, palate, pharynx and epiglottis
Each taste bud is a compact cluster of 50/100 columnar epithelial cells (type I, type II and type III)
Different signalling transduction pathways for different tastes
Type II and II are involved in the sensation of taste
Type I cells act more like glial cells rather than being involved in the sensation of taste, more involved in maintenance of homeostasis for the whole taste bud

Question 16

Type II and III taste bud cells

Answer 16

Type II and II are involved in the sensation of taste

Question 17

Type I taste bud cells

Answer 17

Type I cells act more like glial cells rather than being involved in the sensation of taste, more involved in maintenance of homeostasis for the whole taste bud

Question 18

General cell signal transduction mechanism

Answer 18

1. Interaction of tastant with receptor causes increase in intracellular Ca2+
2. Ca2+ flux causes release of neurotransmitter or signaling molecule which interacts with afferent nerve fibre
   - ATP, GABA, serotonin and Ach are transmitters/ signaling molecules involved in taste signaling in taste buds (taste sense is different with lots of different taste molecules)

Question 19

G-protein mediated signalling in Type II taste cells =

Answer 19

Sweet
Bitter
Umami

Question 20

G-protein mediated signalling in Type II taste cells - Sweet

Answer 20

Homodimer (2 exact isoforms) of the type I receptor

Question 21

G-protein mediated signalling in Type II taste cells - Bitter

Answer 21

Monomer of the type II receptor

Question 22

G-protein mediated signalling in Type II taste cells - Umami

Answer 22

Heterodimer (2 different isoforms) of the type I receptor

Question 23

Shared steps of G-protein mediated signalling in Type II taste cells for sweet, bitter and umami

Answer 23

Activation of G-protein coupled receptor –> Activation of Phospholipase C
And activity of phospholipase C creates an increase in IP3 and IP3 itself binds to its receptor called IP3R3 which sits in the membrane of the endoplasmic reticulum and when it binds it causes the IP3R3 channel to open and calcium is released from the ER into the cytoplasm

Opening of IP3R3 channel and calcium efflux into cytoplasm
Increase of calcium in the cytoplasm and this causes the opening of the channel TRPM5 which causes a sodium influx which causes a change in membrane potential leading to depolarisation

Opening of TRPM5 channel -> sodium influx -> taste cell depolarisation

Opening of CALHM1 channel -> ATP release -> depolarisation of afferent nerve fibres
Depolarisaiton causes the opening of CALHM1 channel
When this channel is opened the cell releases ATP which then binds to receptor on afferent nerve fibres creating an action potential to be sent off to the brain

Question 24

Non G-protein signalling in Type III taste cells =

Answer 24

Sour and salty

Question 25

Steps of Non G-protein signalling in Type III taste cells for sour taste

Answer 25

Stimulated by acids (such as acetic acid or citric acid) Protons enter the cell via a proton-selective channel (Otop1) blocks leaky K+ channels Cell depolarises resulting in the release of neurotransmitter onto terminal of afferent nerve fibre Under normal conditions, Type III taste cells have a leaky potassium channel which allows potassium out of the cell and maintains membrane potential but when these taste cells are exposed to an acid, protons can enter cell through Otop1 which reduces intracellular pH (makes more acidic) and this reduction in pH blocks the leaky potassium channels so potassium can no longer leave the taste cell which leads to depolarisation of the taste cell which allows sodium to come in and causes an action potential and the action potential causes calcium channels to open and cause calcium influx and get neurotransmitter release onto afferent nerve fibres

Question 26

Non G-protein signaling in Type III taste cells: Salt (pretty debated)

Answer 26

NaCl, and Na+ containing compounds Probably sensed by type III taste cells Na+ likely enters through ENaC (epithelial Na+ channel) Into the type III taste cell and causes a depolarisation of the cell and depolarisation causes opening of voltage gated calcium channels and cause influx and the increase in calcium results in the release of vesicles containing neurotransmitter to be released onto the afferent nerve fibres Depolarisation results in release of neurotransmitter onto afferent nerve fibres

Question 27

Central signal transduction pathway

Answer 27

Taste buds innervated by chorda tympani, lingual, trigeminal and glossopharyngeal nerves Afferent fibres synapse in the medulla and then…info… Info relayed to the thalamus, then to the cortex Motor nerve supply to tongue muscles mainly Hypoglossal (allows tongue movement)

Question 28

Other 'tastes'

Answer 28

``` Spicy foods Peppery (pungent) foods Fatty foods Astringent foods Spiciness and pungency do not interact with specific taste receptors and are therefore not thought of as tastes ```

Question 29

Spicy

Answer 29

Hot and spicy “tastes” are sensed by heat and pain-sensitive nerve fibres stimulated by chemicals such as capsaicin and piperine Capsaicin is an active component of chilli peppers Piperine is the alkaloid that gives pepper its pungency

Question 30

Astringent foods

Answer 30

Astringent foods High amount of tannins Popcorn, unripened bananas, pomegranates Causes mucus layers in mouth to contract, leaving your mouth dry

Question 31

Fatty foods

Answer 31

Fatty foods Fats believed to interact with CD36 which then activates phospholipase C …cause IP3 increase…IP3 binds to IP3R3 and causes calcium influx…then signal sent to afferent nerve fibres (NOT going to be heavily tested, still debate)

Question 32

Perception of taste

Answer 32

Our perception of taste is stimulated by the activation of a combination of these receptors Perception of taste is also heavily linked by smell

Question 33

The loss of taste caused by ...

Answer 33

Neurological damage Stroke Smoking Change in form, quantity and vascularization of taste buds Infection e.g. COVID 19

Question 34

Aguesia

Answer 34

Aguesia (the total loss of taste)

Question 35

Dysguesia

Answer 35

Dysguesia (persistent horrible taste in mouth)

Question 36

Hyperguesia

Answer 36

Hyperguesia heightened taste (ABNORMAL)

Question 37

What depolarises type III taste cells

Answer 37

A reduction in intracellular pH

Question 38

When are leaky K+ channels blocked?

Answer 38

When pH reduces

Question 39

Type I cells and taste

Answer 39

not involved in the sensation of taste

Question 40

Glutamate

Answer 40

Glutamate forms a major part of the umami taste response (also other ones, but this is the major one)

Question 41

CALHM1

Answer 41

ATP

Question 42

Otop1

Answer 42

H+/protons into type III taste cells

Question 43

IP3R3

Answer 43

calcium out of ER cells

Question 44

Taste transduction in type II taste cells vs type III taste cells

Answer 44

taste transduction in type II taste cells is G protein mediated but in type III taste cells it is not

Question 45

Angular acceleration =

Answer 45

canals

Question 46

Linear acceleration

Answer 46

utricle and saccule

Question 47

Ossicles function

Answer 47

Transmitting sound waves from outer to inner ear = ossicles