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

What ion is the major component of salt?

Answer 11

→ Na+

Question 12

Describe how saltiness is transduced

Answer 12

→ 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 13

What is the ion component of sourness?

Answer 13

→ H+

Question 14

Describe how sourness is transduced?

Answer 14

→ 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 is elicited and gustatory afferents are activated

Question 15

Describe how bitterness is transduced

Answer 15

→ 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 16

What taste receptors is bitterness detected by?

Answer 16

→ T2 receptors

→ 25 types

Question 17

What are T1/2 receptors coupled with?

Answer 17

→ Gq

Question 18

What receptor detects sweetness?

Answer 18

→ A dimer receptor formed of T1R2+T1R3

Question 19

How is sweetness transduced?

Answer 19

→ Same as bittnerness

Question 20

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

Answer 20

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

Question 21

What receptor detects umami?

Answer 21

→ Dimer receptor formed of T1R1 + T1R3

Question 22

How is umami transduced?

Answer 22

→ Same as bitterness and sweetness

Question 23

What does CN VII transmit information from?

Answer 23

→ Anterior tongue

Question 24

What does CN IX transmit information from?

Answer 24

→ Posterior tongue

Question 25

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

Answer 25

→ Epiglottis

→ Temperature and texture

Question 26

What is the pathway to the gustatory cortex

Answer 26

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

Question 27

What are pheromones?

Answer 27

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

Question 28

What do we smell with?

Answer 28

→ Olfactory epithelium

Question 29

What is the olfactory epithelium?

Answer 29

→ 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 30

What are olfactory receptor cells?

Answer 30

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

Question 31

What are supporting cells?

Answer 31

→ They function like glia and help produce mucus

Question 32

Describe how odorant molecules activate the receptors

Answer 32

→ 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 33

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

Answer 33

→ 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 34

Describe what central olfactory pathways are

Answer 34

→ 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

Question 35

Where does the olfactory bulb project?

Answer 35

→ 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

Question 36

What do the other senses project through?

Answer 36

→ Thalamus

Question 37

What channels are used to detect low concentrations of salt?

Answer 37

→ Amiloride sensitive channels

→ insensitive to voltage and stay open

Question 38

What determines the specificity of sweetness or umami?

Answer 38

→ T1R subunit

Question 39

What are basal cells?

Answer 39

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

Question 40

Describe an example of population coding for olfaction?

Answer 40

→ 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