Lecture 12: Olfactory system Flashcards
M.v.W
How does the olfactory system detect stimuli?
Gas molecules that hit the mucus layer of the nose
What kind of model of receptors are used and why?
Key lock model –> many molecules are hydrophobic so they interact with odoran-binding proteins
Can a receptor detect the whole gas molecule?
No, it can recognize epitopes
What kind of receptors are olfactory receptors?
GPCR (with 7 trans-membrane domains)
Where are ORC located?
Nose roof
How is is that each of us perceives odor slightly different?
There is big variation in olfactory receptor expression due to low selection pressure of OR genes
With what does OCR activation correspond?
Chemical quantity (firing corresponds with quantity)
What is anosmia?
Complete or partial loss of the sense of smell
How does odor specific anosmia happen?
Dysfunction of commonly expressed olfactory receptors
Why do olfactory receptor cells need to be replaced?
Due to direct exposion to noxious environmental stimuli
How does signal transduction work in cilia of olfactory receptor cells?
Oderant molecule —> GPCR activation –> activation of adenylate cyclase –> ATP activates cAMP –> cAMP activates Na+/Ca2+ channel –> Ca2+-CAM + Ca2+ gated Cl- channel can open
- Cl- efflux in the cell must be very high for the cell to depolarize
How does adaptation in ORC work?
- Ca2+-CAM binds to CNG channel and reduces its sensitivity to cAMP.
- Ca2+-CAM activates PDE that destroys cAMP
What is the function of ORC adaptation?
Helps in detection of new odors in environment.
- Olfaction is a difference detector and not a constant chemical sensor
How is the S/N ratio in second neurons improved (neuronal quality)?
Many ORCs expres the same receptor
How can we smell different odors even though a lot of OCRs express the same receptors?
ORCs respond to related molecules with different affinities –> olfactory coding space is high-dimensional - different odors activate different combinations of ORCs
The zonal expression of OR genes in the epithelium is also present in the olfactory bulb. In the bulb are glomuli present. Which cells play an excitatory role and thereby convey information to the olfactory cortex?
Mitral and Tuffled cells (M/T cells)
Which cells are mainly and which fully GABAergic?
Peri-glomerular cells - Granule cells
Which cells make distant lateral connections?
Mitral and granule cells
Which interneurons are also mainly replaced?
PG and Granule cells
(is to some extend activity dependend)
What are possible functions of interneuron replacement (rewiring)?
- Adjust to high ORC turnover
- Adjust sensitivity to changes in stimulus environment
- Support short-term and long-term odor memory
Odors induce synchronized oscillations. Which 3 rhythms do we have?
Fast: Beta and Gamma
Slow: Theta
Why are PNs (second order neurons) important?
They make spatio-temporal encoding of olfactory information possible.
- Odor-evoked activity is distributed in time and space —> activity pattern
Functions of Theta, Beta, Gamma oscillations:
- Theta: Phase is locked to breathing, present in bulb and cortical areas.
- Beta: increases with repeated presentation of odors, associated with learning, also present in bulb and cortical areas
- Gamma: increase in power correlated with olfactory acuity (detection, distinguishing,identification of different odors)
What does the primary olfactory cortex, specifically piriform cortex encode?
Molecular features of odors, associates odors with behavioral features
What is the role of the amygdala in the olfactory system?
- Emotional response to odors
- Innate behavioral reponse (pheromones)
NOTE: input from MOB and accessory OB
What happens in the orbitofrontal cortex?
- Consciousness of smell!
- Associative area of olfaction and taste
- Modulation by physiological state
- Subjective classes pleasent and unpleasent encoded in space
Which brain structure is largely bypassed?
Thalamus
