The Chemical Senses Flashcards

1
Q

What tastes are innately enjoyed and why?

A

→ Sweet and fatty

→ They provide energy

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2
Q

Why is bitterness disliked?

A

→ Taste of bitterness is associated with poison

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3
Q

What are the 5 tastes?

A
→ Sweet
→ bitter
→ sour
→ salt
→ umami
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4
Q

Where are taste buds present other than the tongue?

A

→ Palate

→ Epiglottis

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5
Q

What two types of cell are inside a taste bud?

A

→ Basal cells

→ Taste cells

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6
Q

What are basal cells?

A

→ Juvenile taste cells

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7
Q

What are taste cells and what do they look like?

A

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

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8
Q

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

A

→ Different responses

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9
Q

How are saltiness and sourness transduced?

A

→ Ion channels

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10
Q

How are bitterness, sweetness and umami transduced?

A

→ GPCR via T1 and T2

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11
Q

What ion is the major component of salt?

A

→ Na+

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12
Q

Describe how saltiness is transduced

A

→ 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

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13
Q

What is the ion component of sourness?

A

→ H+

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14
Q

Describe how sourness is transduced?

A

→ 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

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15
Q

Describe how bitterness is transduced

A

→ 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

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16
Q

What taste receptors is bitterness detected by?

A

→ T2 receptors

→ 25 types

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17
Q

What are T1/2 receptors coupled with?

A

→ Gq

18
Q

What receptor detects sweetness?

A

→ A dimer receptor formed of T1R2+T1R3

19
Q

How is sweetness transduced?

A

→ Same as bittnerness

20
Q

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

A

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

21
Q

What receptor detects umami?

A

→ Dimer receptor formed of T1R1 + T1R3

22
Q

How is umami transduced?

A

→ Same as bitterness and sweetness

23
Q

What does CN VII transmit information from?

A

→ Anterior tongue

24
Q

What does CN IX transmit information from?

A

→ Posterior tongue

25
Q

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

A

→ Epiglottis

→ Temperature and texture

26
Q

What is the pathway to the gustatory cortex

A

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

27
Q

What are pheromones?

A

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

28
Q

What do we smell with?

A

→ Olfactory epithelium

29
Q

What is the olfactory epithelium?

A

→ 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

30
Q

What are olfactory receptor cells?

A

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

31
Q

What are supporting cells?

A

→ They function like glia and help produce mucus

32
Q

Describe how odorant molecules activate the receptors

A

→ 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

33
Q

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

A

→ 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

34
Q

Describe what central olfactory pathways are

A

→ 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

35
Q

Where does the olfactory bulb project?

A

→ 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

36
Q

What do the other senses project through?

A

→ Thalamus

37
Q

What channels are used to detect low concentrations of salt?

A

→ Amiloride sensitive channels

→ insensitive to voltage and stay open

38
Q

What determines the specificity of sweetness or umami?

A

→ T1R subunit

39
Q

What are basal cells?

A

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

40
Q

Describe an example of population coding for olfaction?

A

→ 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