Lecture 5: Peripheral Olfaction

Question 1

What is taste/gustation?

Answer 1

strictly what happens through your taste buds

Question 2

What is smell/olfaction?

Answer 2

what happens through your nose

Question 3

What is flavour?

Answer 3

combination of taste, smell, somatosensation/mouth feel, and more that leads to the overall Gestalt of a particular food

Question 4

What are the contributions of the taste system to flavour?

Answer 4

can distinguish if something is sweet and/or sour

(but can’t determine what the food is specifically)

Question 5

What are the contributions of the smell system to flavour?

Answer 5

can distinguish what the food is

• evokes memories
• smell is critical to our perception of food, some things are much more identifiable with than without smell

Question 6

What is a percept?

Answer 6

impression of an object obtained by use of the senses

Question 7

What is the discriminative capacity?

Answer 7

breadth of different stimuli that system can tell apart

Question 8

Describe the anatomy of the olfactory system.

Answer 8

• olfactory epithelium lined with olfactory sensory neurons
• olfactory sensory neurons project to olfactory bulb

Question 9

How do odours enter the nose?

Answer 9

nose knows that odours are sensed in the nasal cavity

smells enter through nostril, then gets absorbed into mucus on membrane (epithelium) and makes contact with receptors to activate neurons

Question 10

What happens when vertebrate odour receptors (GPCRs) are activated?

Answer 10

GPCRs are activated by binding of odour ligand
- activates Golf
- production of cAMP
- active Na+/Ca2+ cAMP-gated ion channel (cation channel) depolarizes the cell
- Ca2+-gated Cl- channel normally hyperpolarizes the membrane because negative ions are entering cells, however because of equilibrium potential of Cl- in cells, Cl- actually exits, causing depolarization

Question 11

How have odorant receptors evolved?

Answer 11

quick evolution of multi-gene families – different species have dramatically different numbers of functional odorant receptors

Question 12

Why might insect odorant receptors be ion channels instead of GPCRs like humans?

Answer 12

they use olfaction for more important things than humans do

Question 13

What is the vertebrate odorant receptor expression pattern?

Answer 13

strictly one per cell

Question 14

What is a glomerulus?

Answer 14

represents a functional unit for olfactory perception

Question 15

What is the receptive field of olfactory receptor neurons?

Answer 15

the specific odour molecules that activate a neuron

Question 16

What is NOT part of the receptive field?

Answer 16

portion of space that the neuron can detect odours from (how much a neuron gets activated depending on where the odour is)

Question 17

What does it mean to be narrowly tuned?

Answer 17

relatively specific for a small number of stimuli

Question 18

What does it mean to be broadly tuned?

Answer 18

respond to wide range of stimuli

Question 19

Is there an odour map (chemotopy) in the mammalian brain (olfactory bulb)?

Answer 19

NO

PROBLEM: odour molecules are notoriously difficult to parameterize
- if we group chemicals based on functional groups, we can see a little bit of rough chemotopy – ie. anterior glomeruli appear more sensitive to aldehydes, while posterior glomeruli appear more sensitive to thiazoles

HOWEVER: plotting response similarity between pairs of glomeruli vs. distance between them (to see if glomeruli with similar activities tend to be close together), there is no significant correlation
- if some property of odour space is mapped, glomeruli that respond to similar odours should be closer together than glomeruli that respond to different odours