Olfactory System

Question 1

What are the 3 chemical senses?

Answer 1

1. smell
2. taste
3. vomeronasal (not in humans)

Question 2

What is smell?

Answer 2

volatile chemicals (food, danger, other animals at a distance)

Question 3

What is taste?

Answer 3

ingested chemicals (discriminates nutritious form toxic)

Question 4

What is vomeronasal?

Answer 4

detects pheromones

Question 5

There are odor primaries (T/F)

Answer 5

False

Question 6

What is the general pathway for olfaction?

Answer 6

1. Olfactory sensory neurons project axon to olfactory bulb
2. Axons pass through cribiform plat
3. Odorants detected on sensory cilia that project into olfactory mucosa

Question 7

What kind of current is the olfaction sensory response?

Answer 7

• inward current

- action potential depolarizaiton

Question 8

Where is the sensory response initiated?

Answer 8

in the cilia

Question 9

3 reasons why humans have lower ability to smell than other animals

Answer 9

1. humans have fewer receptor neurons than dogs
2. humans have fewer receptor genes than mice
3. humans have ~300 genes each encoding different receptor, mice have ~1000

Question 10

What is the olfactory sensory transduction pathway? (6)

Answer 10

1. Receptor binds ligand
2. G protein exchanges GDP for GTP
3. Adenylate cyclase makes cAMP from ATP
4. cAMP opens a CNG (cyclic-nucleotide gated) ion channel
5. Na+ and Ca2+ comes into cell causing depolarization
6. Ca2+ opens Cl- channel, ensuring response in absence of Na+

Question 11

What provides specificity in the olfactory system?

Answer 11

Each receptor binds a different constellation of odorants

Question 12

What kind of receptors are odorants?

Answer 12

G-protein coupled receptors

Question 13

How was it found that odorants are Gprotein coupled receptors?

Answer 13

• Use PCR amplification from olfactory cDNA and primers that recognize all GPCRs

Question 14

What are 4 characterisits of odorant receptors?

Answer 14

1. They are -7 TM G protein coupled
2. encoded in intronless genes
3. scattered throughout the genome
4. number in the hundreds (we have 388 functional receptors)

Question 15

How many genes for odorant receptors?

Answer 15

hundreds

Question 16

How many receptors per neuron?

Answer 16

1 receptor/neuron

Question 17

What kind of distribution of olfactory sensory neurons?

Answer 17

random distribution in olfactory epithelium

-4 zones of expressions, randomly distributed in zones

Question 18

Each neuron responds to _______ and each odorant activates _______

Answer 18

subset of odorants, several receptors

Question 19

What happens in the olfactory bulb?

Answer 19

convergence of axons from olfactory sensory neurons that express same receptor