Olfaction and Gustation

Question 1

Olfaction

Answer 1

Detection of airborne inorganic and organic chemicals (odors)

Question 2

Principles of olfactory systems

Answer 2

Large number of odorant receptors
each OSN expresses only a single OR and each OR has distinct ligand profile
OSNs with same receptor have axons that converge at same glomerulus
each odor encoded combinatorially

Question 3

Mammalian and C. elegans ORs

Answer 3

7 transmembrane GPCRs.

Odor binding results in GPCR signalling and neurone depolarisation

Question 4

Insect ORs

Answer 4

odor gated cation channels that may be modulated by G-protein signalling

Question 5

Drosophila odor coding

Answer 5

axons with same OR converge on glomeruli in antennal lobe

excitatory projections send dendrites to single glomerulus

inhibitory neurons project to multiple glomeruli

Question 6

co-convergence

Answer 6

neurons with different ORs project to same glomerulus

Question 7

co-expression

Answer 7

2 ORs expressed in one OSN

Question 8

Drosophila odor discrimination

Answer 8

Encoder stage at antennal lobe, antenna and maxillary palp

Decoder stage at lateral horn and mushroom body

Question 9

Gustation in the fly

Answer 9

proboscis projects to subesophagael zone
Legs and wings project to ventral nerve chord
abdomen

Question 10

Gustation and feeding

Answer 10

Sucrose detected with leg gustatory neurons
Fly stops and extends proboscis
proboscis labellar neurons detect appetitive substance and cause proboscis extension and injection

Bitter compounds cause proboscis retraction

Question 11

Gustation in mammals

Answer 11

Taste receptor cells (TRC) grouped in taste buds in papillae of tongue and oral cavity

Each bud contains 3 types of TRCs and basal cells for generation of new TRCs

Question 12

Odorant binding proteins

Answer 12

Bind, solubilise and transport hydrophobic stimuli to chemoreceptors across aqueous sensilla lymph

Also found in high concentrations in the nasal mucus of vertebrates