The Chemical Senses

Question 1

What tastes are innately enjoyed and why?

Answer 1

→ Sweet and fatty

→ They provide energy

Question 2

Why is bitterness disliked?

Answer 2

→ Taste of bitterness is associated with poison

Question 3

What are the 5 tastes?

Answer 3

→ Sweet
→ bitter

→ sour
→ salt
→ umami

Question 4

Where are taste buds present other than the tongue?

Answer 4

→ Palate

→ Epiglottis

Question 5

What two types of cell are inside a taste bud?

Answer 5

→ Basal cells

→ Taste cells

Question 6

What are basal cells?

Answer 6

→ Juvenile taste cells

Question 7

What are taste cells and what do they look like?

Answer 7

→ Mature taste cells which have microvilli that project towards the taste pore

Question 8

What would be seen if you took a voltage recording of taste cells?

Answer 8

→ Different responses

Question 9

How are saltiness and sourness transduced?

Answer 9

→ Ion channels

Question 10

How are bitterness, sweetness and umami transduced?

Answer 10

→ GPCR via T1 and T2

Question 11

Describe how saltiness is transduced

Answer 11

→ High Na+ concentration when eating salt
→ Na+ passes through Na+ selective channels down its concentration gradient

→ This depolarises the taste cell and activates voltage gated Ca2+ channels
→ Vesicular release of NT (5-HT) is elicited and gustatory afferents are activated

Question 12

What is the ion component of sourness?

Answer 12

→ H+

Question 13

Describe how sourness is transduced

Answer 13

→ H+ can pass through the same Na+ channels that mediate saltiness
→ H+ blocks K+ sensitive channels

→ Increased H+ and blocking K+ depolarise the cell and activate voltage gated Ca2+ channels
→ Vescicular release of neurotransmitters(5HT) is elicited and gustatory afferents are activated

Question 14

Describe how bitterness is transduced

Answer 14

→ T2 receptors are Gq coupled
→ PLC converts PIP2 → DAG + IP3

→ IP3 activates a type of Na+ channel and releases Ca2+ from the endoplasmic reticulum
→ Depolarises the taste cell and activates voltage gated Ca2+ channels
→ Release of ATP is elicited and gustatory afferents are activated

Question 15

What taste receptors is bitterness detected by?

Answer 15

→ T2 receptors

→ 25 types

Question 16

What are T1/2 receptors coupled with?

Answer 16

→ Gq

Question 17

What receptor detects sweetness?

Answer 17

→ A dimer receptor formed of T1R2+T1R3

Question 18

How is sweetness transduced?

Answer 18

→ Same as bitterness

Question 19

Why do we not confuse bitter, sweet and umami tastes?

Answer 19

→ Taste cells either express bitter or sweet receptors not both
→ Bitter and sweet taste cells connect to different gustatory axons

Question 20

What receptor detects umami?

Answer 20

→ Dimer receptor formed of T1R1 + T1R3

Question 21

How is umami transduced?

Answer 21

→ Same as bitterness and sweetness

Question 22

What does CN VII transmit information from?

Answer 22

→ Anterior tongue

Question 23

What does CN IX transmit information from?

Answer 23

→ Posterior tongue

Question 24

What does CN X transmit information from and what kind of information?

Answer 24

→ Epiglottis

→ Temperature and texture

Question 25

What is the pathway to the gustatory cortex

Answer 25

→ Gustatory nucleus within the medulla → Transmitted to ventral posterior nucleus of the thalamus → projects to the gustatory cortex

Question 26

What are pheromones?

Answer 26

→ Signals for reproductive behaviours, marking territories, indicating aggression or submission

Question 27

What do we smell with?

Answer 27

→ Olfactory epithelium

Question 28

What is the olfactory epithelium?

Answer 28

→ Dendrites of olfactory cells that protrude from the olfactory bulbs through holes called the cribiform plate → they have cilia and are covered in a mucus layer

Question 29

What are olfactory receptor cells?

Answer 29

→ Site of transduction and are genuine neurons unlike taste receptor cells

Question 30

What are supporting cells?

Answer 30

→ They function like glia and help produce mucus

Question 31

Describe how odorant molecules activate the receptors

Answer 31

→ Odorant molecules bind to odorant receptor proteins on the cilia → Olfactory specific Golf G proteins are activated → Adenylyl cyclase activation increases cAMP formation → cAMP activated channels open allowing Na+ and Ca2+ influx → Ca2+ activated chloride channels open enabling Cl- efflux → Olfactory cells have a high concentration of Cl- ions so they diffuse out

Question 32

Describe the changes in action potential frequency from the nerve to the cilia

Answer 32

→ AP propagate continously along the olfactory axon → receptor potential propagates along dendrite and triggers AP within the soma → Odorants generate a slow receptor potential in the cilia

Question 33

Describe what central olfactory pathways are

Answer 33

→ Odor molecules bind to olfactory receptor proteins → These transmit to different cells in the olfactory bulbs → Olfactory cells expressing the same receptor proteins project to the same glomeruli → the glomeruli converge onto common pathways → transmitted to higher regions of the brain

Question 34

Where does the olfactory bulb project?

Answer 34

→ Frontal cortex - perception of what smell is → hypothalamus and amygdala give you emotional aspect of the smell such as a memory which is coupled to the hippocampus → hippocampus gives odour memory

Question 35

What do the other senses project through?

Answer 35

→ Thalamus

Question 36

What channels are used to detect low concentrations of salt?

Answer 36

→ Amiloride sensitive channels | → insensitive to voltage and stay open

Question 37

What determines the specificity of sweetness or umami?

Answer 37

→ T1R subunit

Question 38

What are basal cells?

Answer 38

→ Immature olfactory receptor cells - source of new olfactory receptor cells

Question 39

Describe an example of population coding for olfaction

Answer 39

→ When presented with a citrus smell none of the receptor cells can individually distinguish it from other odours → the brain can distinguish the citrus smell through combination of responses from all 3 cells

Question 40

What is population coding?

Answer 40

the responses of a large number of broadly tuned neurons are used to specify the properties of a particular stimulus

Question 41

What are the different papillae on the tounge?

Answer 41

→Ridge-shaped (foliate) →Pimple-shaped (vallate) →Mushroom-shaped (fungiform)