8. CHEMICAL SENSES Flashcards
(37 cards)
1
Q
Define gustation
A
- Gustation refers to taste
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
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
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
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
6
Q
What are the three types of papillae found on the tongue?
A
- FOLLIATE - Ridge shaped
- VALLATE - Pimple shaped
- FUNGIFORM - Mushroom shaped
7
Q
What are the four components of taste buds?
A
- TASTE RECEPTOR CELLS
- BASAL CELLS
- TASTE PORE
- GUSTATORY AFFERENTS - transmit information to other areas
8
Q
What are basal cells of the taste bud?
A
- Precursor to taste receptor cells
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
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
11
Q
What are the 5 types of taste?
A
- SALTINESS
- SOURNESS
- BITTERNESS
- UMAMI
- SWEETNESS
12
Q
What are the two types of transduction mechanisms for taste?
A
- ION CHANNEL - Saltiness, sourness
2. GPCR MECHANISMS - Bitterness, sweetness, umami
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
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
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
16
Q
Which three types of taste use GPCR?
A
- Bitterness
- Sweetness
- Umami
17
Q
What are the two classes of GPCR taste receptors?
A
- T1R
- 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
- Bitter tastant binds to T2R which is a G-protein coupled receptor associated with PLC
- Gq activates PLC which converts PIP2 -> IP3 + DAG
- IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
- Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
- Gustatory afferents activated
23
Q
**What is the transduction mechanism for SWEETNESS?
A
- Sweet tastant binds to T1R1-T1R3 dimer which is a G-protein coupled receptor associated with PLC
- Gq activates PLC which converts PIP2 -> IP3 + DAG
- IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
- Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
- Gustatory afferents activated
24
Q
**What is the transduction mechanism for UMAMI?
A
- Umami tastant binds to T1R2-T1R3 dimer which is a G-protein coupled receptor associated with PLC
- Gq activates PLC which converts PIP2 -> IP3 + DAG
- IP3 causes an intracellular increase in Ca2+ AND acts on Na+ channels specific to taste cells
- Influx of Ca2+ & Na+ causes membrane depolarisation which releases ATP. ATP passes through ATP permeable channel
- Gustatory afferents activated
25
Why don't we confuse bitterness sweetness & umami if they all have the same transduction mechanism?
- 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
Which three cranial nerves are involved in gustation?
- 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
**Describe the pathway of taste information from the cranial nerves to the brain?
Cranial nerves -> Gustatory nucleus -> Ventral posterior medial nucleus (thalamus) -> Gustatory cortex
28
Define olfaction
- Olfaction refers to the sensation of smell
29
What are pheromones?
- Pheromones are olfactory stimuli used for connection between individuals
30
What are the three cells of the olfactory epithelium?
- 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
What are olfactory receptor cells?
- 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
What are the basal cells of the olfactory epithelium?
- The basal cells are the immature olfactory receptor cells
| - They are one of the only type of neural cells that can regenerate
33
What are the supporting cells of the olfactory epithelium?
- 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
Describe the steps for the transduction mechanism for OLFACTION
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
Describe the action potentials of olfactory receptor cells?
- Odorants generate a slow action potential in the cilia
| - In the olfactory receptor cells, there's propagation of the action potentials
36
Describe the flow of olfactory information to the brain
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
What is population coding?/
- 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
