Chemical Senses

Question 1

What are the chemical senses?

Answer 1

taste

smell

Question 2

What are the 5 basic tastes?

Answer 2

salt, sweet, sour, bitter, umami

Question 3

What is the distribution of taste cells?

Answer 3

bits of tongue are more sensitive to some tastes but no real distribution

Question 4

what are taste buds?

Answer 4

groups of taste cells

Question 5

Where are taste buds found?

Answer 5

tongue, palate, pharynx

Question 6

what are taste cells not?

Answer 6

sensory neurones (they look like a synpase but they aren’t a synapse because they have no neurone)

Question 7

What happens when a chemical binds to a taste cell?

Answer 7

1. chemical binds
2. transduction occurs causing a receptor potential
3. depolarisation
4. voltage gated calcium channels open
5. calcium entry
6. neurotransmitter released
7. excites sensory neurone
8. action potential

Question 8

How is salt detected?

Answer 8

1. sodium entry causes depolarisation through leak channels

2. if there is a high conc of Na+ it causes an action potential

Question 9

How is sour detected?

Answer 9

• H+ ions can either enter through TRP

- or H+ block K+ channels causing depolarisation

Question 10

How are sweet, umami and bitter detected?

Answer 10

• G protein coupled receptors
• subunits are T1R and T2R family
• unique combination of each subunit for each taste

Question 11

What is the sweet combination?

Answer 11

T1R2 T1R3

Question 12

Umami combination?

Answer 12

T1R1 and T1R3

Question 13

Bitter combination?

Answer 13

T2R T2R

Question 14

What is the central taste pathway?

Answer 14

gustatory sensory axons

cranial nerves

brainstem

thalamus

primary gustatoty cortex

Question 15

What are the secondary pathways for taste and what are they used for?

Answer 15

-medulla
responsible for salivation and swallowing

-hypothalamus

for satiety (fullness)
palatability (how nice it is)

Question 16

Where are the smells receptors?

Answer 16

small receptors in the olfactory epithelium

Question 17

Are olfactory cells neurones?

Answer 17

yes

Question 18

How many types of receptor does each olfactory cell have?

Answer 18

one

Question 19

Can receptor molecules bind to more than one odourant?

Answer 19

yes

Question 20

What is population coding?

Answer 20

any one neurone will detect its own unique bunch of smells

Question 21

Why do you get used to cells?

Answer 21

because the olfactory neurone can adapt quickly to the presence of a smell

Question 22

How is it transduced?

Answer 22

single mechanism for all receptors:

odourant binds to receptor

G protein mediated events

Intracellular cascade

Na+/Ca+ channels open

depolarisation

receptor potential

Question 23

Where is the olfactory bulb?

Answer 23

glomerulus

Question 24

What is the central olfactory pathway?

Answer 24

olfactory neurones

olfactory bulb

olfactory cortex

can go to either:

limbic areas (associates information e.g smell of place)

MD thalamus to orbitofrontal cortex (recognition and combining smell and taste)