Olfaction in Insects and Animals/ Smell n Taste 3

Question 1

What does ORN stand for?

Answer 1

Olfactory receptor neuron

Question 2

What kind of cilia does each ORN contain and what are they bathed in?

Answer 2

Non-motile cilia bathed in mucus that covers the olfactory epithelium. They also contain receptors

Question 3

What do the unmyelinated axons of the ORN become?

Answer 3

Primary olfactory nerve fibre that passes through the cribriform plate and first synapses in the olfactory bulb

Question 4

What is an odorant?

Answer 4

Chemicals that can dissolve in the nasal mucus - gives an odour to something. May be water soluble or hydrophobic

Question 5

How are odorants bound and how is stimulation stopped?

Answer 5

By odorant binding proteins and once neuron stimulated you have to remove the odorant to stop stimulation

Question 6

Give an example of the metabolic proteins that odorant binding proteins help with the secretion of.

Answer 6

Cytochrome P450, dehydrogenases, oxidases, esterase’s

Question 7

Explain the process of olfactory transduction.

6 marks

Answer 7

• Odorant binds to OBP which activates a receptor
• Receptor receives appropriate ligand and undergoes conformational change activating a G-protein
• Activated G-protein activates adenyl cyclase which makes cAMP, and cell depolarises
• cAMP acts on Ca2+ gated ion channels
• Channel opens allowing Ca2+ and Na+ to come into the cilia of a neurons causing depolarisation
• Ca2+ causes further depolarisation by acting on Ca2+ gated Cl- channels, Cl- leaves neuron causing further depolarisation

Question 8

What happens when adenyl cyclase doesn’t function properly?

Answer 8

Have reduced cAMP an maybe develop complete anosmia

Question 9

What can you use to possibly reduce the affects of anosmia/ restore some scent function?

Answer 9

Using phosphodiesterase inhibitors

Question 10

What can be observed in fMRI when presented with different odours?

Answer 10

Different patterns of brain activity within the olfactory bulb

Question 11

What are the five basic tastes?

Answer 11

Salt, Sour, Sweet, Bitter and, Umami

Question 12

What particular amino acid is the umami taste associated with?

Answer 12

Glutamate and aspartate

Question 13

How are taste buds arranged on the tongue?

Answer 13

In groups of 30-100 elongated neuroepithelial cells (not neurons). Embedded in papillae (not always)

Question 14

What is at the apex of the taste bud and below its apex?

Answer 14

At apex is microvillar processes that protrude through small opening - taste pore
Below apex is taste cell joined by tight junctional complexes which prevent gaps between cells

Question 15

What are the 2 theories to the specificity of taste?

Answer 15

Either have a specific taste bud detects one specific taste. Or have multiple taste receptors that line one taste bud

Question 16

What do the taste cells do after a chemical comes through the pore?

Answer 16

Communicate/ innervate with neurons

Question 17

How many members are there to the bitter receptor family and what cells are they expressed in?

Answer 17

50-80 members, expressed in cells that also express the G-protein involved in the cascade (alpha-gustducin)

Question 18

What are the characteristics of sweet and umami receptors?

Answer 18

Made up of a combination of different subunits, coded for by gene family T1Rs

Question 19

What receptors are ‘for’ umami taste?

Answer 19

T1R1+3 Amino acid receptor

Question 20

What receptors are ‘for’ a sweet taste?

Answer 20

T1R2+3 - sweet receptor. T1R3 may be a sweetener receptor on its own

Question 21

What other ‘tastes’ are there where their detection hasn’t fully been established as of yet?

Answer 21

Fat-CD36 this is an integral membrane protein on cell surface that binds fat.
Astringency - feelings of unripe fruit (bitterness, sour taste sort of)