Lecture 24 Taste Flashcards
What are the two chemical senses?
Taste and smell
What is the stimulus for taste?
chemicals
The sensations of taste and smell arise in response to what?
contact with chemicals in the environment, either what we put in our mouths (tastes), or that we inhale (odours)
What are the cells that detect the chemical stimuli of tastes and smells?
chemoreceptors
What do the chemical senses do?
allow us to detect chemicals in the environment that might help us survive and fulfil our biological destiny
What is our biological destiny?
find food, avoid poisons, find a compatible mate to pass on our genes
Which tastes is often deemed to be poinsonous?
bitter
Describe the taste buds on the tongue
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
What is the purpose of the microvilli around the pores?
to assess the environment of the mouth at that time
Where are the taste buds located?
in the taste pores, where the chemoreceptors are
What is the epithelium that lines the side of the tongue?
foliate papillae
There are 8 or 9 large papillae at the back of the tongue. What are these called?
vallate papillae
As well as on the tongue, where else do we have taste buds?
on the roof of the mouth (the palate), the pharynx, and epiglottis
What are the 5 different tastes?
Sweet, sour, salty, bitter, umami
What is the umami taste stimulated by?
amino acids, especially glutamate
What is the bitter taste stimulated by?
alkaloids like in spinach and lettuce
What’s the sweet taste stimulated by?
sugars and artificial sweeteners
What is the sour taste stimulated by?
acids, mostly organic ones
What is the salty taste stimulated by?
by Na+ containing compounds
What is each taste bud a cluster of?
50/100 columnar epithelium cells
What are the three types of columnar epithelium cells that make up a taste bud?
Type |
Type ||
Type |||
What is the role of Type | epithelium cells?
these are not involved in taste, these act more as glial cells for the homeostasis of the taste bud
How do we distinguish between different tastes?
there are different transduction pathways for different tastes (but there is a general mechanism)
Describe the general cell transduction mechanism
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
What are some examples or neurotransmitter/signalling molecules involved in taste signalling in taste buds?
ATP, GANA, serotonin and ACh are transmitter/signalling molecules involved in taste signalling in the taste buds
Humans can detect 5 different tastes BECAUSE humans have 5 different types of taste cell
the first statement is true and the second statement is false
Type || cells are involved in the detection of which tastants?
bitter, sweet, umami
What type of signalling pathway does the Type || taste cells do?
G-protein coupled
Describe the G-protein mediated signalling in type || taste cells
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
How can we distinguish between sweet, bitter and umami if they are all activating type || taste cells?
Each type || taste cell can only detect one of these three tastants and is distinguished by the makeup of the T2R or T1R receptor
How does the makeup of the T1R or T2R receptors differ between the type || taste cells that detect umami, sweet and bitter tastants?
- 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
What two tastants stimulate type ||| taste cells?
sour and salty
What type of signalling is used in type ||| taste cells?
non g-protein receptor signalling
Describe the non G-protein signalling in type ||| cells used to detect sour tastant
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
Which of the three taste cell types acts most like a neuron?
Type |||
Describe the non G-protein signalling in type ||| cells used to detect a salty tastant
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.
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
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.
List 4 other “tastes”
Spicy, peppery, fatty, astringent
Why are these other “tastes” not considered real tastes?
Because they do not interact with specific taste receptors
What are hot and spicy “tastes” sensed by?
heat and pain-sensitive nerve fibres stimulated by chemicals such as capsaicin and piperine
What are astringent foods and how are they detected?
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.
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 ________ ________.
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.
What are three examples of losses of taste?
aguesia, dysguesia and hyperguesia
What is aguesia?
the complete loss of taste
What is disguesia?
the persistant horrible taste in mouth
What is hyperguesia?
the partial loss of one type of taste
What causes these losses in taste?
neurological damage (eg. a stroke), smoking (changes in form, quantity and vascularisation of taste buds), infection
A reduction in intracellular pH depolarises type || cells BECAUSE the leaky K+ channels are blocked when pH reduces
the first statement is false and the second statement is true
