Olfaction (smell) Flashcards
Where are the olfactory neurons located?
In the olfactory epithelium (in the nasal cavity)
Where are the mitral cells located, and how are they connected to the olfactory neurons?
In the olfactory bulb (a bone right above the olfactory epithelium). They are forming synapses with the olfactory neurons in olfactory glomeruli in the olfactory bulb. The OCs are coming through the cribriform plate.
Which areas are the mitral cells projecting to, and how are the signals percieved?
1) the olfactory cortex: conscious perception of smell
2) the hippocampus: olfactory memory
3) the amygdala: emotional response
4) the reticular formation: visceral response
5) the hypothalamus: homeostasis
How many different odorant receptors is there, and which type of receptor are they?
App. 300 GPCRs. And each olfactory cell only express one type of odorant receptor.
Explain the smell transduction.
Odorant binds to OR, and the G-olf-alfa (G_s) activates an adenylyl cyclase, that converts ATP to cAMP. cAMP gates a CNG channel, inducing a Ca^2+ influx. Ca^+ gates a Cl^- channel, inducing Cl^- efflux (high Cl^- conc. in olfactory cells). Ca^2+ influx + Cl^- efflux results in an action potential.
How is the signal stopped?
1) G-olf-beta-gamma subunit activates a GRK, which phosphorylates and inhibits the GPCR, 2) cAMP activates a PKA, which phosphorylates and inhibits the GPCR, 3) Ca^+ inhibits the adenylyl cyclase, 4) Ca^2 binds to calmodulin, and CaM inhibits the CNG channel
Why is it important to stop the signal?
It’s important for animals to be able to smell new smells quite fast, and to be able to differentiate between multiple smells.
