Taste and Smell Flashcards
1
Q
How many taste buds do humans have?
A
4000
2
Q
Where are taste buds found?
A
- Tongue
- Cheeks
- Soft palate
- Pharynx
- Epiglottis
3
Q
Types of lingual papillae
A
- Filiform
- Foliate
- Fungiform
- Vallate
4
Q
Filiform papillae
A
- Spiked
- No taste buds
- Most abundant
5
Q
Foliate papillae
A
- Least abundant
- Gone by 2-3 years
6
Q
Fungiform papillae
A
- ~3 apical taste buds
- Especially at tip and sides of tongue
7
Q
Vallate papillae
A
- Large
- Back of tongue
- Contain about half of all taste buds (approx 200 buds each)
8
Q
Taste transduction - salty
A
- Salt-sensitive taste cells have selective Na+ channels (not voltage gated) which are open all the time
- When you taste something salty, extracellular Na+ concentration rises and so the gradient across the membrane is made steeper
- Na+ moves into the cell causing membrane depolarisation
9
Q
Anions effect on salt taste
A
The larger the anion the less salty the food will taste as it inhibits the salt taste of the cation
10
Q
Taste transduction - sour
A
- High in acidity
- H+ permeates the Na+ channel, inward H+ flow and depolarisation
- H+ binds to and blocks K+ sensitive channels, depolarises the cell
11
Q
Taste transduction - sweet
A
- Some molecules become sweet when they bind to specific receptor sites and activate cascade of second messengers
- GPCR triggers formation of cAMP within cytoplasm, activates protein kinase A which phosphorylates a K+ selective channel causing a blockade, this depolarises the receptor cell (similar to activation of noradrenaline receptor in some neurons)
- Some sweet stimuli activate pathway which involves IP3
- May also be mechanism which doesn’t involve second messengers, set of cation channels gated by sugars
12
Q
Taste transduction - bitter
A
- Bitter taste receptors are often poison receptors
- Some bitter substances bind directly to K+ channels and block them
- Also specific membrane receptor proteins for bitter substances which activate GPCR IP3 mechanisms
- IP3 mechanism modulates transmitter release without changing the membrane potential
- Another bitterness mechanism reduces cAMP by activating enzymes which break down cAMP
13
Q
Taste transduction - umami
A
- Comes from glutamate or aspartate
- Glutamate directly activates an ion channel that is permeable to the cations Na+ and Ca2+, causing depolarisation, opening voltage-gated Ca2+ channels which triggers transmitter release
- Glutamate binds to GPCRs which decrease cAMP levels which in turn modify some unknown channel
14
Q
Olfactory system
A
- Sensitive
- Detect 2000-4000 odours
- Sensory cells are neurons
- Molecule binds receptor, opens Na+ channels, second receptor cAMP
- Adapt quickly, synaptic inhibition
15
Q
What do we smell with?
A
- Olfactory epithelium
- Small, thin sheet of cells high up in the nasal cavity
