Lecture 24 Taste

Question 1

What are the two chemical senses?

Answer 1

Taste and smell

Question 2

What is the stimulus for taste?

Answer 2

chemicals

Question 3

The sensations of taste and smell arise in response to what?

Answer 3

contact with chemicals in the environment, either what we put in our mouths (tastes), or that we inhale (odours)

Question 4

What are the cells that detect the chemical stimuli of tastes and smells?

Answer 4

chemoreceptors

Question 5

What do the chemical senses do?

Answer 5

allow us to detect chemicals in the environment that might help us survive and fulfil our biological destiny

Question 6

What is our biological destiny?

Answer 6

find food, avoid poisons, find a compatible mate to pass on our genes

Question 7

Which tastes is often deemed to be poinsonous?

Answer 7

bitter

Question 8

Describe the taste buds on the tongue

Answer 8

the bumps on the tongue are called papillae and taste pores are holes that surround the papillae. Around the pores, there are hairs called microvilli

Question 9

What is the purpose of the microvilli around the pores?

Answer 9

to assess the environment of the mouth at that time

Question 10

Where are the taste buds located?

Answer 10

in the taste pores, where the chemoreceptors are

Question 11

What is the epithelium that lines the side of the tongue?

Answer 11

foliate papillae

Question 12

There are 8 or 9 large papillae at the back of the tongue. What are these called?

Answer 12

vallate papillae

Question 13

As well as on the tongue, where else do we have taste buds?

Answer 13

on the roof of the mouth (the palate), the pharynx, and epiglottis

Question 14

What are the 5 different tastes?

Answer 14

Sweet, sour, salty, bitter, umami

Question 15

What is the umami taste stimulated by?

Answer 15

amino acids, especially glutamate

Question 16

What is the bitter taste stimulated by?

Answer 16

alkaloids like in spinach and lettuce

Question 17

What’s the sweet taste stimulated by?

Answer 17

sugars and artificial sweeteners

Question 18

What is the sour taste stimulated by?

Answer 18

acids, mostly organic ones

Question 19

What is the salty taste stimulated by?

Answer 19

by Na+ containing compounds

Question 20

What is each taste bud a cluster of?

Answer 20

50/100 columnar epithelium cells

Question 21

What are the three types of columnar epithelium cells that make up a taste bud?

Answer 21

Type |
Type ||
Type |||

Question 22

What is the role of Type | epithelium cells?

Answer 22

these are not involved in taste, these act more as glial cells for the homeostasis of the taste bud

Question 23

How do we distinguish between different tastes?

Answer 23

there are different transduction pathways for different tastes (but there is a general mechanism)

Question 24

Describe the general cell transduction mechanism

Answer 24

First, there is an interaction of a tastant (eg. sweet, salty etc.) with its receptor which causes an increase in the intracellular Ca2+. This Ca2+ influx causes the release of a neurotransmitter or signally molecule which interacts with different afferent nerve fibres

Question 25

What are some examples or neurotransmitter/signalling molecules involved in taste signalling in taste buds?

Answer 25

ATP, GANA, serotonin and ACh are transmitter/signalling molecules involved in taste signalling in the taste buds

Question 26

Humans can detect 5 different tastes BECAUSE humans have 5 different types of taste cell

Answer 26

the first statement is true and the second statement is false

Question 27

Type || cells are involved in the detection of which tastants?

Answer 27

bitter, sweet, umami

Question 28

What type of signalling pathway does the Type || taste cells do?

Answer 28

G-protein coupled

Question 29

Describe the G-protein mediated signalling in type || taste cells

Answer 29

The tastant (sweet, bitter and umami) interact with the receptor (T2R or T1R) which activates the G-protein coupled receptor. This activates phospholipase C. This causes an increase in IP3 which binds to receptors IP3Rs in the membrane of the endoplasmic reticulum. This causes this channel to open and Ca2+ is released from the ER into the cytosol. This increase in Ca2+ concentration stimulates the opening of TRPM5, a channel in the membrane. This opening allows Na+ to enter the cell which is depolarising. This depolarisation opens CALHM1 which allows ATP to be released from the cell. ATP binds to receptors on afferent nerve fibres which causes an action potential

Question 30

How can we distinguish between sweet, bitter and umami if they are all activating type || taste cells?

Answer 30

Each type || taste cell can only detect one of these three tastants and is distinguished by the makeup of the T2R or T1R receptor

Question 31

How does the makeup of the T1R or T2R receptors differ between the type || taste cells that detect umami, sweet and bitter tastants?

Answer 31

- bitter binds to a monomer of the type 2 receptor - sweet binds to a homodimer of the type 1 receptor - umami binds to a heterodimer of the type 1 receptor

Question 32

What two tastants stimulate type ||| taste cells?

Answer 32

sour and salty

Question 33

What type of signalling is used in type ||| taste cells?

Answer 33

non g-protein receptor signalling

Question 34

Describe the non G-protein signalling in type ||| cells used to detect sour tastant

Answer 34

These are stimulated by acids (such as acetic acid or citric acid). Type ||| cells have leaky K+ channels so K+ can leave and maintain RMP. When exposed to acids, H+ enters through a channel (OTOP1) so there is a decrease in the pH in the cell. This decrease in pH blocks the K+ channels and so K+ can't leave. This is depolarising in the cell and it causes Na+ to enter the cell which causes an action potential. This stimulates the influx of Ca2+ ions into the cell and there is neurotransmitter release onto afferent nerve fibres

Question 35

Which of the three taste cell types acts most like a neuron?

Answer 35

Type |||

Question 36

Describe the non G-protein signalling in type ||| cells used to detect a salty tastant

Answer 36

These are stimulated by Na+ containing compounds. Na+ enters the cells through the ENaC (epithelial Na+ channel). This causes a depolarisation which results in the release of neurotransmitter onto afferent nerve fibres.

Question 37

Describe the central signal transduction pathways the taste buds are innervated by a number of nerve fibres such as the l_______, t_____ and g_______ nerves. The afferent fibres from these nerve synapse at the _______ and the information is relayed to the _________, then to the ______. The motor nerve to the tongue muscles is mainly from the ____________ nerve

Answer 37

The Taste buds are innervated by a number of nerve fibres such as the lingual, trigeminal and glossopharyngeal nerves. The afferent fibres from these nerve synapses in the medulla and the information is relayed to the thalamus, then to the cortex. The motor nerve supply to the tongue muscles is mainly from the hypoglossal nerve.

Question 38

List 4 other "tastes"

Answer 38

Spicy, peppery, fatty, astringent

Question 39

Why are these other "tastes" not considered real tastes?

Answer 39

Because they do not interact with specific taste receptors

Question 40

What are hot and spicy "tastes" sensed by?

Answer 40

heat and pain-sensitive nerve fibres stimulated by chemicals such as capsaicin and piperine

Question 41

What are astringent foods and how are they detected?

Answer 41

Astringent foods contain high amounts of tannins (eg. popcorn, unripened bananas and pomegranates). These have lots of phenols which cause the mucus layer in the mouth to contract, leaving your mouth dry.

Question 42

How are fatty foods detected? Fatty foods interact with the _________ which interacts with ___________ but we don't know _______ this is (whether it's a ____________ or not). __________ activates ______ which binds to the ________ receptor on the ________ ____________ which causes the release of _____ into the ______. This causes the opening of ______ which allows _______ into the cell which causes a _________ and this allows a _________ to be released but we don't know ________ ________.

Answer 42

Fatty foods interact with the CD36 which interacts with phospholipase C but we don't know how this is, whether it's a G-protein coupled receptor or not. Phospholipase C activates IP3 which binds to the IP3R3 on the endoplasmic reticulum which causes the release of Ca2+ into the cytosol. This causes the opening of TRPM5 which allows Na+ into the cell which is depolarising. This depolarisation allows a neurotransmitter to be released but we don't know which one.

Question 43

What are three examples of losses of taste?

Answer 43

aguesia, dysguesia and hyperguesia

Question 44

What is aguesia?

Answer 44

the complete loss of taste

Question 45

What is disguesia?

Answer 45

the persistant horrible taste in mouth

Question 46

What is hyperguesia?

Answer 46

the partial loss of one type of taste

Question 47

What causes these losses in taste?

Answer 47

neurological damage (eg. a stroke), smoking (changes in form, quantity and vascularisation of taste buds), infection

Question 48

A reduction in intracellular pH depolarises type || cells BECAUSE the leaky K+ channels are blocked when pH reduces

Answer 48

the first statement is false and the second statement is true