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Intro to Neuroscience > L21 The Chemical Senses > Flashcards

L21 The Chemical Senses Flashcards

1
Q

What is the most common and oldest form of sense?

A

Chemical sense

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2
Q

Why is the difference between the gustatory system and the olfactory system?

A

Gustatory system - taste
Olfactory system - smell

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3
Q

What are the functions of the chemical sense?

A

Functions:
* Identify food sources
* Avoid noxious substances
* Find a mate or mark territories

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4
Q

What are the five basic tastes of the gustatory system?

A
  1. Salty
  2. Sour
  3. Sweet
  4. bitter
  5. Unami(Savoury).
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5
Q

What is the relation and relevance of the salty taste?

A

Relates to vital electrolytes. Required for many physiological processes

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6
Q

What is the relation and relevance of the sour taste?

A

Relates to acidity - H+ content
Relevance - avoid rotting food, injury to GI tract

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7
Q

What is the relation and relevance of the sweet taste?

A

Sweet relates to sugars
Relevant for required for energy and growth

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8
Q

What is the relation and relevance of a bitter taste?

A

Relates to diverse chemical structures
Relevance - avoid toxic substances, poisonous

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9
Q

What is the relation and relevance to the unami (savoury) taste?

A

Umami relates to amino acids e.g. glutamate which is relevant for protein synthesis, neurotransmission etc

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10
Q

What does the Lingual papillae contain?

A

They contain taste buds which are a group of taste cells.

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11
Q

Which taste organs can contains taste buds?

A

Taste organs = primarily tongue, also cheeks, soft palate, pharynx, epiglottis

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12
Q

How many chemo receptive taste cells are there per taste bud?

A

Approx. 100

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13
Q

How does taste pore allows sensory transduction?

A

Taste pore allows sensory transduction by microvilli

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14
Q

How many taste buds do we have ?

A

2000-5000 taste buds

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15
Q

What is the transduction of different stimuli dependent on?

A

Each different taste stimuli are dependent on which membranous receptors are expressed

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16
Q

Which 5 taste of the gustatory system uses an ionic receptor or a g coupled protein receptor?

A

Ionic receptors - Salty and sour
G - protein coupled receptors - Bitter sweet and unami.

17
Q

Describe the specificity of taste cells and taste buds

A

Taste buds contain various taste cells which respond to various stimuli’s

Taste cells appear to only to respond to one type of stimuli

18
Q

What are gustatory afferent cells?

A

Gustatory afferents are sensory nerve fibers that transmit information from the taste buds in the mouth to the brain

19
Q

How are the Gustatory afferent cell’s mechanism different to taste cells?

A

Taste cells require neurotransmitter release across the synaptic cleft whereas Gustatory cells trigger an action potential

20
Q

What are the 3 main parts of the olfactory system?

A
  • Olfactory epithelium
  • Olfactory
  • bulb
  • Olfactory cortex
21
Q

How many odorants can be detected and what is the size of the human olfactory epithelium?

A
  • Odorants as low as a few parts per trillion can be detected
  • Human olfactory epithelium = 10 cm^2
22
Q

How are olfactory receptor cells classed as bipolar chemoreceptive neurons?

A
  • Bipolar structure: Single dendrite extending towards the olfactory cilia and axon extending towards olfactory bulb
  • Chemorecptive neurons: Role is to detect chemicals (odorants) in the air
23
Q

What does a transduction machinery do?

A

This machinery is responsible for converting the chemical signal of an odorant molecule into an electrical signal that the brain can interpret as smell

24
Q

Where is the transudction machinery found?

A

Transduction machinery is found within the cilia at the end of the dendrite

25
What must the Odorants do to reach the olfactory receptor cells?
Odorants must dissolve in the mucus layer to reach olfactory receptor cells
26
What is the primary afferent neuron of the olfactory receptor cell?
Primary afferent neuron is the axon. The axon is thin and unmyelinated
27
Do olfactory receptor cells remain for the whole adult lifetime?
Olfactory receptor cells are one of the few types of neurons that are regularly replaced in adults
28
How many odorant receptor proteins do humans have?
Humans have ~350 odorant receptor proteins
29
What does ORs stand for?
Odorant receptor proteins (ORs)
30
Can one type of odorant receptor recognise multiple odorants?
Yes. Receptors have flexibility in their bindings site. Think of induced fit
31
Can olfactory receptor cells only express one type of odorant receptor?
Yes. Cells can only go to its complementary receptor
32
How do we recognises an odorant?
It is the unique combination of odorant receptors that recognise an odorant that allows us to distinguish a specific odor
33
Are odorant receptor proteins (ORs) G-protein coupled or ion channel receptors?
They are G protein coupled receptors
34
Briefly explain the process of G protein coupled receptor activation
1) Ligand binding: A signalling molecule binds to GPCR 2) Conformational change 3) G protein activation: GPCR interacts with G protein which causes it to exchange GDP for GTP 4) Activated G protein detaches from GPCR and splits into alpha and beta subunits 5) Activated alpha or beta subunit activates effector proteins like adenyly cyclase 6) Adenylyl cyclase triggers production of second messengers like cAMP
35
Explain the downstream pathway for Olfactory receptors (OR)
1) Odorant molecule binds to specific OR located on the cilia of olfactory cell 2) ORs are GPCRs so conformational change, activating G protein, which triggers adenylyl cyclase, which triggers cAMP 3) cAMP binds to cyclic ncueltodie-gates (CNG) channels on the plasma membrane which allows selective cation (K+/ Ca2+) to flow into the cell 4) This cause depolarisation as inside becomes less negative 5) Opening of Calcium-activated chloride channels (CaCCs) due to influx of Ca2+ so Cl- ions flow out of the cell, further contributing to depolarisation
36
What happens if there’s an intense stimulus?
Intense stimulus detected by large receptor potential which than expresses increased frequencies of action potential firing rate

Intro to Neuroscience (28 decks)

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