Chemical Senses

Question 1

What are the chemical senses?

Answer 1

taste

smell

Question 2

What is the importance of chemical detection (Chemoreceptors)?

Answer 2

Finding food
Finding mates
Avoiding dangerous substances
Homeostasis

Question 3

What are the submodalities of Taste?

Answer 3

salt, sweet, sour, bitter, umami

Question 4

What is the distribution of taste cells?

Answer 4

distributed all over the tongue (no absolute regions) however some areas have a higher density of taste cells for a specific modality

Question 5

what are taste buds?

Answer 5

groups of taste cells

Question 6

Where are taste buds found?

Answer 6

tongue, palate, pharynx

Question 7

what are taste cells not?

Answer 7

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

Question 8

What are some properties of tase cells?

Answer 8

Taste receptors (not neurones)

Constantly replaced (every 2 weeks)

Have various transduction mechanisms depending on the submodality type

Question 9

What happens when a chemical binds to a taste cell?

Answer 9

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 10

How is salt detected?

Answer 10

1. sodium entry causes depolarisation through leak channels

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

Question 11

How is sour detected?

Answer 11

• H+ ions can either enter through TRP

- or H+ block K+ channels causing depolarisation

Question 12

How are sweet, umami and bitter detected?

Answer 12

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

Question 13

What is the combination of GPCRs for the modality of sweet?

Answer 13

T1R2 and T1R3

Question 14

What is the combination of GPCRs for the modality of Umami?

Answer 14

T1R1 and T1R3

Question 15

What is the combination of GPCRs for the modality of Bitter?

Answer 15

T2R and T2R

Question 16

What is the central gustatory (taste) pathway?

Answer 16

gustatory sensory axons (1’ neurone)

cranial nerves

Synapse in brainstem (gustatory nucleus) (2’neurone)

Synapse in thalamus (3’ neurone)

primary gustatoty cortex

Question 17

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

Answer 17

-medulla
responsible for salivation and swallowing

-hypothalamus

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

Question 18

What does the neural coding of taste do?

Answer 18

Comparison from all taste inputs

Gives a general taste of substances

Question 19

Which is more sensitive, taste or smell?

Answer 19

Smell is much more sensitive than taste

Question 20

Where are the smells receptors?

Answer 20

small receptors in the olfactory epithelium in the nose

Question 21

Are olfactory cells neurones?

Answer 21

yes

Question 22

How many types of receptor does each olfactory cell have?

Answer 22

1

Question 23

Can receptor molecules bind to more than one odourant?

Answer 23

yes

Question 24

What are some properties of olfactory cells?

Answer 24

They are neurones

replaced every 4-8 weeks

1 type of receptor molecule per olfactory cell

Each receptor molecule can bind to a range of odorants

Question 25

How are smells detected?

Answer 25

Signal transduction

- Single mechanism for all receptors

Question 26

What is a key speciality of olfactory neurones?

Answer 26

Rapidly adapting and therefore will lose sensitivity of an environment the longer the cells are exposed to it.

Question 27

how is an action potential generated in an olfactory cell to detect smell?

Answer 27

Odorant binds to receptor

G-protein mediated events

intracellular cascade

Na/Ca channels open

depolarisation (receptor potential)

passes threshold

Action potential

Question 28

What is the olfactory bulb?

Answer 28

Location of the 1st synapse of the primary neurone.

Neurones of a similar range of molecules synpase close together in the glomerulus.

Question 29

What is the central olfactory pathway?

Answer 29

olfactory neurones (1’ neurone)

olfactory bulb (2’ neurone)

olfactory cortex

Question 30

Where can the olfactory pathway lead to after the signal has reached the olfactory cortex?

Answer 30

Limbic areas (associate information with emotion eg. smell of a place)

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