Olfactory System Flashcards
What are the 3 chemical senses?
- smell
- taste
- vomeronasal (not in humans)
What is smell?
volatile chemicals (food, danger, other animals at a distance)
What is taste?
ingested chemicals (discriminates nutritious form toxic)
What is vomeronasal?
detects pheromones
There are odor primaries (T/F)
False
What is the general pathway for olfaction?
- Olfactory sensory neurons project axon to olfactory bulb
- Axons pass through cribiform plat
- Odorants detected on sensory cilia that project into olfactory mucosa
What kind of current is the olfaction sensory response?
- inward current
- action potential depolarizaiton
Where is the sensory response initiated?
in the cilia
3 reasons why humans have lower ability to smell than other animals
- humans have fewer receptor neurons than dogs
- humans have fewer receptor genes than mice
- humans have ~300 genes each encoding different receptor, mice have ~1000
What is the olfactory sensory transduction pathway? (6)
- Receptor binds ligand
- G protein exchanges GDP for GTP
- Adenylate cyclase makes cAMP from ATP
- cAMP opens a CNG (cyclic-nucleotide gated) ion channel
- Na+ and Ca2+ comes into cell causing depolarization
- Ca2+ opens Cl- channel, ensuring response in absence of Na+
What provides specificity in the olfactory system?
Each receptor binds a different constellation of odorants
What kind of receptors are odorants?
G-protein coupled receptors
How was it found that odorants are Gprotein coupled receptors?
• Use PCR amplification from olfactory cDNA and primers that recognize all GPCRs
What are 4 characterisits of odorant receptors?
- They are -7 TM G protein coupled
- encoded in intronless genes
- scattered throughout the genome
- number in the hundreds (we have 388 functional receptors)
How many genes for odorant receptors?
hundreds
