Lecture 24- Taste Flashcards
What two senses are known as the chemical senses? What are their purpose?
- Taste (gustation)
- Smell (olfaction)
Vital from an evolutionary standpoint so that we avoid eating things that could be poisonous (usually taste bitter/ rancid). Also play a role in finding a compatible mate so can pass on genes.
What cells are responsible for detecting the stimulants (chemicals) in taste and smell?
Chemoreceptors
What are the bumps on the tongue called? What are the two large bumps at the back? And at the sides?
- Papilla
- At back= vallate papilla
- At sides= Foliate papilla
What sits underneath the papilla (folds of epithelium)?
Taste pores, taste hairs then taste buds
What structure is responsible for the sensation of taste?
Taste buds
What are the 5 tastes? What are they stimulated by?
- Sweet: stimulated by sugars
- Sour: stimulated by acids
- Salty: stimulated by sodium (NaCl)
- Bitter: complex, but typically stimulated by alkaloids
- Umami: stimulated by amino acids, especially glutamate
Is it true that different parts of the tongue are sensitive to different tastes?
Yes but it is not as distinct as the taste maps you were shown in primary school
How many taste buds do we have and where?
2000-5000 taste buds, on tongue, palate, pharynx and epiglottis
What do taste buds consist of?
Compact cluster of 50/100 columnar epithelial cells (type I, type II and type III)
Which of the types of cells that make up taste buds are the tasting cells and which are the support/ glial cells?
- Type 1= support/ glial
- Type 2 + 3= taste cells
What is the general cell signal transduction mechanism?
- Interaction of tastant with receptor causes increase in intracellular Ca2+
- Ca2+ flux causes release of neurotransmitter or signaling molecule which interacts with afferent nerve fibre
Is there just one neurotransmitter invovled in the sensation of taste?
No, there are many…
ATP, GABA, serotonin and Ach are transmitters/ signaling molecules involved in taste signaling in taste buds
Humans can detect 5 different tastes BECAUSE Humans have 5 types of taste cell
A – Both answers are correct and causally related
B – Both answers are correct but not causally related
C – First statement is true but second is false
D – First statement is false but second is true
E- Both statements are false
C- first statement is true but second is false
What three tastes are related in that they all involve G-protein mediated signaling in type 2 taste cells?
- Bitter
- Umami
- Sweet
Describe the pathway for sweet….
- Tastant interacts with a homodimer of the type 1 receptor
- Activation of G-protein coupled receptor –> Activation of Phospholipase C
- Opening of IP3R3 channel and calcium efflux into cytoplasm
- Opening of TRPM5 channel leads to sodium influx leads to taste cell depolarization
- Opening of CALHM1 channel leads to ATP release leads to depolarization of afferent nerve fibres
Describe the pathway for bitter…
- Tastant interacts with a monomer of the type 2 receptor
- Activation of G-protein coupled receptor –> Activation of Phospholipase C
- Opening of IP3R3 channel and calcium efflux into cytoplasm
- Opening of TRPM5 channel leads to sodium influx leads to taste cell depolarization
- Opening of CALHM1 channel leads to ATP release leads to depolarization of afferent nerve fibres
Describe the pathway for umami…
- Tastant interacts with a heterodimer of the type 1 receptor
- Activation of G-protein coupled receptor –> Activation of Phospholipase C
- Opening of IP3R3 channel and calcium efflux into cytoplasm
- Opening of TRPM5 channel leads to sodium influx leads to taste cell depolarization
- Opening of CALHM1 channel leads to ATP release leads to depolarization of afferent nerve fibres
How does non G-protein signaling in type 3 cells work for sour tastants?
- Stimulated by acids (such as acetic acid or citric acid)
- Protons enter the cell via a proton-selective channel (Otop1) which decreases pH and blocks leaky K+ channels (positive charge cannot leave)
- Cell depolarizes (Na+ coming in) resulting in the release of neurotransmitter onto terminal of afferent nerve fiber + action potentials
How does non G-protein signaling in type 3 cells work for salty tastants?
- NaCl, and Na+ containing compounds
- Probably sensed by type III taste cells
- Na+ likely enters through ENaC (epithelial Na+ channel)
- Depolarisation results in release of neurotransmitter onto afferent nerve fibres
This one is still controversial (not a lot is known!)
What is the central signal transduction pathway?
- Taste buds innervated by chorda tympani, lingual, trigeminal and glossopharyngeal nerves (lots of different types of nerves!)
- Afferent fibres synapse in the medulla
- Info relayed to the thalamus, then to the cortex
What is the motor supply for the tongue muscles called?
Hypoglossal
Are spicy or peppery (pungent) foods considered tastes?
- No as they do not interact with specific taste receptors
- They are instead sensed by heat and pain-sensitive nerve fibers stimulated by chemical such as capsaicin (chilis) and piperine (peppers).
What are astringent foods? Why do we ‘taste’ them but they are not considered one of the actual tastes?
- High amount of tannins e.g. Popcorn, unripened bananas, pomegranates
- causes mucus layers in mouth to contract, leaving your mouth dry
Why are fatty foods hypothesized as the ‘sixth’ taste?
-They may interact with the specific receptor CD36 and then follow a similar process as sweet, bitter and umami aside from the fact that no-one knows whether it is G proteins coupled to activate phospholipase C or something else occurs
