Chapter 8 Chemical Senses: Taste

Question 1

What are the common steps of all 5 senses?

Answer 1

1. Physical stimulus
2. Set of events by which stimulus is transduced into a set of nerve impulses
3. A response to the message

Question 2

Why do animals need chemical senses?

Answer 2

To identify nourishment, poison, potential mate

Question 3

Which are chemical sense?

Answer 3

Gustation and Olfaction

Question 4

What are appetitive tastes?

Answer 4

Sweet- sugars/carbohydrates provide metabolic energy
Umami- meaty/savory taste
Salty- senses ions critical for cellular function

Question 5

What are aversive tastes?

Answer 5

Bitter- Senses a broad-spectrum of potentially poisonous
Sour- common sense to rotten food
Too salty- excessive salt causes dehydration

Question 6

Where are the taste receptors?

Answer 6

Tongue, pharynx, palate and epiglottis

Question 7

What locations on tongue are there taste buds?

Answer 7

Circumvallate, foliate, fungiform

Question 8

What are the distinct anatomical types?

Answer 8

Type I, Type II, Type III cells

Question 9

What are taste cells?

Answer 9

Taste cells are not neurons but some cells have voltage-gated Na+ channels and can generate APs

Question 10

What is the simple process of a taste bud?

Answer 10

Taste cells in taste buds transduce sensory stimuli into signals that are sent to the brain via the gustatory nerves

Question 11

Where are microvilli?

Answer 11

Microvilli at the apical end poke into taste pore-receptors on microvilli

Question 12

What is a Type I cell?

Answer 12

Glial-like support cells
dark
long apical microvilli

Question 13

What is a Type II cell?

Answer 13

They are receptor cells.
Express metabotropic receptors for sweet, bitter, and umami
Cells tend to be narrowly tuned to a single taste quality
“Light”
Short apical microvilli

Question 14

What is a Type III cell?

Answer 14

They are presynaptic cells.
Express receptors for sour and salty taste
This cell on average responds to about 3 taste qualities
single think apical process

Question 15

What receptors do Type II cells use?

Answer 15

They use G-protein-coupled receptors

Question 16

What is the process of transduction for Type II cells? Steps 1-5

Answer 16

1. Molecules activate taste receptor.
2. The receptor activates G-protein (gustducin)
3. G-protein activates PLC
4. PLC sends second messengers DAG and IP3
5. Second messengers activate Ca2+ to be released.

Question 17

What is the process of transduction for Type II cells? Steps 6-10

Answer 17

6. Ca2+ opens calcium dependent cation channel
7. Na+ flows through channel causing depolarization.
8. Depolarization opens voltage-gates Na+ channels .
9. Na+ flows through, depolarizing causing an action potential.
10. Releases ATP (transmitter) through hemichannel. (non-vesicular release)

Question 18

What are the channels for Type III salty cell?

Answer 18

Epithelial Na+ channel, ENaC and Amiloride-Insensitive Na+ channel (AI)

Question 19

What is an Epithelial Na+ channel?

Answer 19

It is inhibited by amiloride.
Low activation threshold

Question 20

What is an Amiloride-Insensitive Na+ channel?

Answer 20

Higher threshold of activation
Receptor unknown

Question 21

What is the transduction mechanism for salty Type III cell?

Answer 21

1. Amiloride-sensitive sodium channel allows Na+ through.
2. Na+ flows through causing membrane depolarization.
3. Depolarization activates voltage-gated sodium channel and calcium channel.
4. Causing vesicle fusion so serotonin-filled synaptic vesicles are released.
5. They form conventional synapses with gustatory nerves where serotonin is released.

Question 22

What is the transduction mechanism for sour Type III cell?

Answer 22

1. Depolarization of apical membranes by a proton current
2. Intracellular acidification results in membrane depolarization by inhibiting a K+ channel
3. Voltage-gates Na+ and Ca2+ opening causing vesicle fusion.
4. So serotonin filled vesicles released into gustatory afferent axon.

Question 23

What is the labelled-line model?

Answer 23

The model that says that receptor cells for sweet, bitter, and umami express only one type of receptor and the taste bud is a structure of parallel independent processing units.

Question 24

How does Type II cells communicate with gustatory nerve?

Answer 24

Type II cells express hemichannels for non-vesicular release of the neurotransmitter ATP for cell-cell communication and communication with gustatory nerve. Since ATP receptor are found on gustatory afferents innervating taste buds.

Question 25

Why do some Type III cells respond to multiple taste qualities?

Answer 25

Type II cell activation by sweet or bitter or umami causes release of ATP. ATP release is necessary for communication with gustatory nerves and can also activate neighboring Type III cells.

Question 26

What is the across-fibre model?

Answer 26

The taste bud is a collective unit involving extensive cell-to-cell interactions.

Question 27

How do we code for tastants?

Answer 27

Population coding

Question 28

What is population coding?

Answer 28

Different tastes have different spatial and temporal patterns of activation in cortex, and this is presumed to be the neural “fingerprint” of the taste.

Question 29

How does the brain process taste?

Answer 29

The brain sorts through the population activity and allows us to perceive many different tastes-even new ones.

Question 30

What are the cranial nerves involved in gustatory?

Answer 30

Anterior tongue (VII), Posterior tongue (IX), and Epiglottis

Question 31

How does the taste reach the gustatory cortex?

Answer 31

The anterior tongue, posterior tongue, and epiglottis afferents neurons reach the gustatory nucleus. The gustatory nucleus reaches the VPM and then makes to the gustatory cortex.