B&B Smell and taste Flashcards
What do sensory systems do?
Represent vast information from the environment
This is relevant to animal’s survival and reproduction
Different animal species have different sensory worlds
How do tsetse flies taste?
Taste hairs
There are components in sweat that stimulate tarsal taste neurones
Describe an insect’s NS
CNS
Visceral nervous system
Peripheral nervous system
Describe an insect’s brain
Mushroom body Located in the protocerebrum Centre of sensory integration and memory formation Optic lobe in protocerebrum Antennal lobe in deutocerebrum Also, a tritocerebrum
What is a sensillum?
A sensory organelle
A companion sensillum is a mechanical stress detector
A typical insect sensillum is one or several bipolarsensory neurones which are tightly enveloped by the glia-like thecogen cell.
This is partly enclosed by the trichogen and tormogen cells
How does a sensillum develop?
eg epidermal eg trichogen
Cells arise via differential mitoses from an epidermal sensillum mother cell
The trichogen cell secretes the cuticle of the sensory hair
The tormogen cell forms the hair socket
When the cuticle is formed, both cells retract
They form the subcuticular sensillum lymph cavity and excrete the sensillum lymph
The olfactory sensilla that hold the sensory neurones are called?
Olfactory receptor neurones
Found in antennae and in maxillary palps
How can the electrical activity of sensory neurones be measured?
Electrophysiological experiments
APs generated by the sensory neurones in response to an odour stimuli are recordered
Electrode and amplifier
Describe a dose response curve
Physiological responses of sensory organs increase with increasing dose of stimuli
What is the EC50?
The measure of the potency of a stimulus
Or the sensitivity of a receptor to it
The dose at which 50% of the maximal effect is reached
What is the molecular basis of odour specificity in insects?
Thought they would be G proteins like vertebrates
Now know they are a novel type of ligand gated ion channels
7 transmembrane domain receptors (like g protein coupled receptors)
They are flipped in the membrane
True or false
An insect olfactory receptor forms a tetramere
True
True or false
Most odours are encoded as an activation pattern across receptors and some odours are encoded by the activity of a single type of receptor.
True
Describe across fibre pattern coding
The message is coded in the pattern of activity across different sensory neurons
Describe labeled line coding
The message is coded in the activity of a single type of sensory neuron
What is bombykol used for?
Pheromone of the silk moth
Released into the wind
Another silk moth follows the scent
What is male love dust?
Aphrodisiac that makes females receptive
Male flies above female and dusts it
What are intraspecific phermones? (phermones are intraspecific)
What are interspecific allelochemicals? (allelochemicals are interspecific)
Act within species
Act between species
What does semiochemicals mean?
Communication by chemicals
There are 3 main types of allelochemicals Kairomones Allomones Synomones Describe them
k = benefit the receiver, disadvantage the producer (host odours for tseste flies) a = neutral to receiver, benefit producer (plant chemicals, deter feeding by insects) s = benefit receiver and producer (flower odours attracting pollinators)
What did Gottfried 2009 find?
Humans can turn a stimulus to a percept even if there are many volatile components, absence of some components, additional components or weak stimuli
What is the approximate number of OR genes in
Mouse
Human
Drosophilia
1100
350
60
What is pseudogenisation?
Mutations that render a gene non functional
True or false
2-8% of Ors are psuedogenes with 50% of human V2Rs being psuedogenes
False
15-78%
All V2Rs
Vertebrate ORs fall into 2 categories
What are these
Class 1 olfactory receptors (tuned to water soluble odorants) Class II (tuned to hydrophobic odours) Amphibians have both class 1 and class II In dolphins, Class II receptors have been psuedogenised - do not have class 1
Are vertebrate olfactory receptors G protein coupled receptors or novel type of ligand gated ion channels?
G protein coupled receptors
Describe Linda Buck and Richard Axel’s discovery of odour receptors
Dissected out olfactory epithelium
Extracted RNA
Reverse transcription to generate cDNA
Used pairs of degenerate primers for GPCRs to amplify further candidate members of the GPCR superfamily olfactory epithelium
Gel electrophoresis, look for banding pattern. Looked for multiple bands - all bands together added up to more of the expected length
That indicated they amplified a family of different DNA strands - encode a family of different receptors - represents family of olfactory receptors
Describe ORNs
Olfactory receptor neurones
Each ORN has 8-20 non motile cilia
The other end of the ORN has an unmyelinated axon
10-100 axons form into a bundle
Each bundle becomes a primary olfactory nerve fibre
The fibre passes through the cribriform plate
The first synapse is in the olfactory bulb
What is an odorant?
May be hydrophilic or hydrophobic Most are volatile (stimulus?) Dissolves in nasal mucous Diffuses to receptors on cilia Aided by odorant binding proteins (OBP) Clearance also aided by OBP
Describe olfactory transduction
OBP and odorant bind
Activate the receptor - 7TM-GPC
It receives an appropriate ligand
Undergoes a confirmational change
Thereby activated g protein
This activates adenyl cyclase
Generates cAMP
This cAMP acts on CNG-cation channels to open the channel
Allows sodium and calcium to come into the cilia of the neuron
Causes depolarisation
The calcium causes further depolarisation by acting on calcium activated chloride channels
Cl- leaves neurone and causes further depolarisation
Why do we perceive taste?
Drives appetite
Protects us from poison
Taste for sugar - absolute requirement for carbohydrates
Cravings for salt because we need sodium chloride in our diet
Why do bitter and sour taste cause aversive, avoidance reactions?
Most poisons are bitter and as food decays, it goes acidic
Why does umami drive our appetite for amino acids?
Meaty, savoury taste and we need proteins
Amino acids are the building block for proteins
What are the 5 basic tastes?
Sweet Sour Bitter Salt Umami
In mammals, taste buds are groups of 30-100 individual elongated cells - what are these cells called?
Neuroepithelial cells
Often embedded in papillae
At the apex of the taste bud, microvillar processes protrude through a small opening called?
The taste pore
Below the taste bud apex, taste cells are joined by tight junctional complexes that prevent gaps between cells
What 3 forms do the papillae come in?
Circumvallate
Foliate
Fungiform
True or false
Different tastes are detected by different parts of the tongue
False
Spread out
What are the two models that describe how taste buds are arranged?
Labeled line model
Access fibre model
Describe the labeled line model
Sweet taste cell, bitter taste cell etc
Describe the access fibre model
Each taste cell has a mixture of receptors eg sweet,bitter,salty
Which model is most likely to describe how taste buds are arranged?
Labeled line model
Limited number of receptor kinds
Describe the bitter receptor family - T2Rs
50-80 members
Expressed in cells that also express alpha-gustducin (that is probably the g protein that is involved in the cascade of detecting bitterness)
70% of gustducin cells in circumvallate and foliate papillae express T2Rs
Describe sweet and umami receptors
Heteromeric receptors made up of a combination of different subunits
Coded for by a small gene family T1Rs
All 3 T1R genes are expressed selectively in human taste receptor cells in the fungiform papillae
This is consistent with their role in taste perception
Sweet and umami receptors T1R1 + 3 = T1R2 + 3 = T1R3 on its own = Umami is possibly mediated by both what and what receptors?
amino acid receptor = umami
sweet receptor
may be the sweetener receptor
mGluR4 and T1R1+3 receptors
Fat CD36 is an integral membrane protein on cell surface. What does it do?
Binds fats
Has a role in fatty acid metabolism, taste and dietary fat processing in the intestine
Lingual lipase reduces triglycerides to what?
mono and di-glycerides and free fatty acids (FFA)
What do FFAs do?
Free fatty acids
Inhibit delayed-rectifier channels in taste cells
What is astringency taste?
Unripe fruit tastes, tannins and oxalic acid
Tannic acid produced as a defense against insects - activates specific neurones in the brain
This suggests it could be considered a separate flavour/taste
What is metallic taste?
eg Cu2+, FeSO4 or blood in mouth
Some drugs can cause this taste
eg metronizadole, acetazolmadide
