Olfaction

Question 1

Did olfaction evolve separately in vertebrates and invertebrates?

Answer 1

Yes!

Question 2

Gustatory is the sense of _____.

Answer 2

Taste

Question 3

In insects, where are the olfactory organs?

Answer 3

On antenna or antennules

Question 4

What are the antenna and antennules of insects covered with?

Answer 4

Sensilla, hairlike projections of the cuticle

Question 5

What are the two proposed mechanisms for olfaction reception in flies?

Answer 5

• ionotropic
• metabotropic

Question 6

How do worms “smell”?

Answer 6

Using their amphid sensory organ

Question 7

Where is the olfactory organ located in vertebrates?

Answer 7

The roof of the nasal cavity

Question 8

Are olfactory receptor cells in vertebrates multipolar neurons?

Answer 8

​No they are bipolar neurons. One end in the olfactory epithelia layer and the other passes through the bony cribiorm plate to synapse with neurons in olfactory bulb in the brain.

Question 9

How is the outer surface of olfactory receptor neurons in vertebrates is highly modified?

Answer 9

• covered in cilie that project into the mucus layer (increase surface area)
• cilia are non-motile
• cilia contain odorant receptor proteins

Question 10

Describe how we smell?

Answer 10

1. ​Odourants bing to receptors
2. Olfactory receptor cells are activated and send electric signals
3. The signals are relayed in glomeruli
4. The signals are transmitted to higher regions of the brain

Question 11

Describe signal transduction in vertebrate olfaction.

Answer 11

• GPCR
• cAMP pathway
  
  • opens cyclic nucleotide-gated calcium channels (CNGC)
  • influx of Ca²⁺
  • opens calcium activates chloride channels (CaCC)
  • efflux of Cl^-
  • depolarization

Question 12

What are the mechanisms of inactivation of olfaction pathways?

Answer 12

• receptor phosphorylatoin by protein kinase A
• inhibition of AC by Ca-calmodulin-dependent kinase
• hydrolysis of cAMP by PDE
• removal of Ca by Ca-Na exchanger

Question 13

Can one odorant can excite more than one neuron?

Answer 13

Yes!

Question 14

What is the unique plasticity of vertebtrate olfactory sensory neurons?

Answer 14

• most sensory systems are limited and fixed number of receptors
• odor receptors undergo constant renewal, being replaced every 6-10 weeks
• population of olfactory stem cells
  
  • 10,000-30,000 new olfactory neurons per day

Question 15

What are pheromones?

Answer 15

Chemical signals released by one animal that affet the behaviour of another animal of the same species

• maintenance of social heirarchies
• stimulation of reproduction

Question 16

What is the pheromone sense organ?

Answer 16

The vomeronasal organ - structurally and molecularly distinct from primary olfactory epithelium.

Question 17

Where is the VNO located in mammals?

Answer 17

Near the base of the nasal cavity near the septum.

Question 18

Where is the VNO located in reptiles?

Answer 18

On the palate with a narrow tube connecting to either the nasal or oral cavity.

Question 19

Pheromones activate which second messenger cascade?

Answer 19

Phospholipase C