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PHYS - NEURO > 8. CHEMICAL SENSES > Flashcards

8. CHEMICAL SENSES Flashcards

1
Q

Define gustation

A
  • Gustation refers to taste
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2
Q

Is taste innate or learned?

A
  • Most of our taste preferences are innate such as a liking of sweet & avoidance of bitterness due to evolutionary reasons
  • However, we can learn to like tastes such as coffee
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3
Q

What organs are involved in taste?

A
  • Taste is a primary function of the tongue but other organs such as the palate, epiglottis, pharynx & nasal cavity are involved
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4
Q

What is the palate?

A
  • The palate refers to the roof of the mouth which separates the oral cavity from the nasal cavity
  • Taste buds can be located in the palate
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5
Q

What is the epiglottis?

A
  • The epiglottis is the leaf shaped structure that covers the laryngeal inlet & prevents food from entering the windpipe when swallowing
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6
Q

What are the three types of papillae found on the tongue?

A
  1. FOLLIATE - Ridge shaped
  2. VALLATE - Pimple shaped
  3. FUNGIFORM - Mushroom shaped
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7
Q

What are the four components of taste buds?

A
  1. TASTE RECEPTOR CELLS
  2. BASAL CELLS
  3. TASTE PORE
  4. GUSTATORY AFFERENTS - transmit information to other areas
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8
Q

What are basal cells of the taste bud?

A
  • Precursor to taste receptor cells
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9
Q

What is the taste pore?

A
  • The taste pore is the chemically sensitive end of the taste receptor cells that interacts with the tastants
  • Microvilli protrude from the taste pore to interact with the tastants
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10
Q

What are taste receptor cells?

A
  • Taste receptor cells express different types of receptor, predominantly one
  • The taste receptor cells can become depolarised & the electrical signal can be passed on to gustatory afferents
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11
Q

What are the 5 types of taste?

A
  1. SALTINESS
  2. SOURNESS
  3. BITTERNESS
  4. UMAMI
  5. SWEETNESS
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12
Q

What are the two types of transduction mechanisms for taste?

A
  1. ION CHANNEL - Saltiness, sourness

2. GPCR MECHANISMS - Bitterness, sweetness, umami

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13
Q

Describe the steps of the transduction mechanism for SALTINESS

A
  • Salt is detected as Na+
    1. Na+ enters the taste cell via Na+ selective channels (Amiloride channels) down the concentration gradient
    2. Na+ influx causes depolarisation of the taste cell
    3. This activates voltage gated Ca2+ & Na+ channels
    4. Na+ & Ca2+ causes vesicular release of neurotransmitter serotonin
    5. Gustatory afferents are activated & pass on signals to other regions
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14
Q

What are amiloride cahnnels?

A
  • Amiloride channels are Na+ selective channels found on taste receptor cells
  • they can detect low levels of Na+ and are insensitive to voltage
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15
Q

Describe the steps for the transduction mechanism of SOURNESS

A
  • Sourness is detected as H+
    1. H+ enters the taste cell via proton channels down the concentration gradient
    2. H+ binds to & blocks K+ channels
    3. The influx of H+ causes membrane depolarisation
    4. Depolarisation activates voltage gated Ca2+ & Na+ channels
    7. Na+ & Ca2+ influx causes vesicular release of neurotransmitter
    8. Gustatory afferent axons are activated
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16
Q

Which three types of taste use GPCR?

A
  1. Bitterness
  2. Sweetness
  3. Umami
17
Q

What are the two classes of GPCR taste receptors?

A
  1. T1R
  2. T2R
    - These receptors also have sub-types but they are G-protein coupled
    - They are coupled to Gq = Phospholipase C
18
Q

What are the GPCR Taste receptors for bitterness?

A
  • T2R

- Multiple sub-types, could be an evolutionary adaptation to avoid bitter tastes that could potentially be poison

19
Q

What are the GPCR Taste receptors for umami?

A
  • T1R1-T1R3

- The receptor is a dimer

20
Q

What are the GPCR taste receptors for sweetness?

A
  • T1R2-T1R3

- The receptor is a dimer

21
Q

Which taste receptor sub-unit differentiates between sweetness & umami?

A
  • Both sweetness & umami have a T1R3 sub-unit but the T1R1 or T1R2 is what distinguishes them
  • T1R = umami
  • T1R2 = sweetness
22
Q

**What is the transduction mechanism for BITTERNESS?

A
  1. Bitter tastant binds to T2R which is a G-protein coupled receptor associated with PLC
  2. Gq activates PLC which converts PIP2 -> IP3 + DAG
  3. IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
  4. Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
  5. Gustatory afferents activated
23
Q

**What is the transduction mechanism for SWEETNESS?

A
  1. Sweet tastant binds to T1R1-T1R3 dimer which is a G-protein coupled receptor associated with PLC
  2. Gq activates PLC which converts PIP2 -> IP3 + DAG
  3. IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
  4. Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
  5. Gustatory afferents activated
24
Q

**What is the transduction mechanism for UMAMI?

A
  1. Umami tastant binds to T1R2-T1R3 dimer which is a G-protein coupled receptor associated with PLC
  2. Gq activates PLC which converts PIP2 -> IP3 + DAG
  3. IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
  4. Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
  5. Gustatory afferents activated
25
Q

Why don’t we confuse bitterness sweetness & umami if they all have the same transduction mechanism?

A
  • Although bitterness, sweetness & umami have the same transduction mechanism they have different receptors
  • The tastants would bind to different receptors depending of whether they’re bitter, sweet or umami
  • The taste receptor cells also express different receptors
  • Different gustatory afferents would also be activated depending on the taste
26
Q

Which three cranial nerves are involved in gustation?

A
  • CRANIAL NERVE 7,9 & 10 synapse with the gustatory nucleus to detect taste
  • Cranial nerve 7 (facial nerve) = detection of taste in the anterior tongue
  • Cranial nerve 9 (glossopharyngeal) = detection of taste in the posterior tongue
  • Cranial nerve 10 (vagus nerve) = from the epiglottis
27
Q

**Describe the pathway of taste information from the cranial nerves to the brain?

A

Cranial nerves -> Gustatory nucleus -> Ventral posterior medial nucleus (thalamus) -> Gustatory cortex

28
Q

Define olfaction

A
  • Olfaction refers to the sensation of smell
29
Q

What are pheromones?

A
  • Pheromones are olfactory stimuli used for connection between individuals
30
Q

What are the three cells of the olfactory epithelium?

A
  • the olfactory epithelium is found within the nasal cavity
  • The olfactory epithelium contains cilia which interact with the odorants
  • It consists of three cell types:
    1. BASAL CELLS
    2. SUPPORTING CELLS
    3. OLFACTORY RECEPTOR CELLS
31
Q

What are olfactory receptor cells?

A
  • Olfactory receptor cells are located in the olfactory epithelium of the nasal cavity
  • It is the site of transduction for olfaction, and has genuine neurones which project into the CNS
32
Q

What are the basal cells of the olfactory epithelium?

A
  • The basal cells are the immature olfactory receptor cells

- They are one of the only type of neural cells that can regenerate

33
Q

What are the supporting cells of the olfactory epithelium?

A
  • The supporting cells of the olfactory epithelium produce mucus containing antibodies & enzymes
  • The odorants dissolve in the mucus before contacting the cilia of olfactory receptor cells
34
Q

Describe the steps for the transduction mechanism for OLFACTION

A
  1. Odorants bind to olfactory receptor proteins on the cilia
  2. This activates the olfactory specific G protein Golf which is coupled to adenylate cyclase
  3. Adenylate cyclase produces cAMP
  4. cAMP activated channels open, leading to a Na+ & Ca2+ influx
  5. The Ca2+ ions open Ca2+ mediated Cl- channels leading to a Cl- efflux
  6. Membrane depolarisation of olfactory receptor cell
35
Q

Describe the action potentials of olfactory receptor cells?

A
  • Odorants generate a slow action potential in the cilia

- In the olfactory receptor cells, there’s propagation of the action potentials

36
Q

Describe the flow of olfactory information to the brain

A

Oflactory receptor cells -> Olfactory nerve (CNI) -> Olfactory bulb

  • The olfactory bulb projects to:
    1. Frontal cortex - conscious perception of smell
    2. Hypothalamus/Amygdala - motivational & emotional aspect of smell
    3. Hippocampus -odour memory
  • Glomeruli within the olfactory bulb are where axons from olfactory receptor cells converge with those of the olfactory bulb, they tend to express the same receptor
37
Q

What is population coding?/

A
  • Population coding is when responses of a large group of broadly tuned neurones are tuned to specify the properties of a a particular stimuli
  • Gustatory & Olfactory axons & the neurones respond broadly

PHYS - NEURO (18 decks)

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