Olfaction Flashcards
What detects airborne odorants?
The olfactory epithelium in the nasal cavity
How do some species enlarge the olfactory epithelium
Turbinates
They also improve airflow contact
What happens to odorants that reach the olfactory epithelium
Dissolve in the mucus film (possibly in association with an odorant binding protein) and then interact with receptors on the olfactory cilia
How often are olfactory receptors renewed?
Every 60 days by basal cell division
Whete does olfactory transduction take place
How does it work (give the cascade)
In the olfactory cilia
- The odorant interacts with the receptor molecule (a GPCR) which activates Golf (a G protein)
- Golf stimulates AC to produce cAMP
- cAMP opens cyclic nucleotide gated cation channels in the ciliary membrane, allowing Ca2+ and Na+ to enter and depolarise the cell, firing APs
- Ca2+ open Ca2+ gated Cl- channels and Cl- ions exit the cell, augmenting the depolarisation
does the receptor current change with [odorant]?
Current increases as [odorant] increases
Which ion is principally involved in olfactory adaptation
What is the mechanism
Ca2+
Calcium acts via calmodulin to reduce the sensitivity of the cation channels to cAMP thus contributing to olfactory adaptation
How is Ca2+ extruded from olfactory receptor cells
Na+/Ca2+ exchanger
Ca2+ ATPase May contribute in some species
True or false
Each olfactory receptors cell expresses only one receptor molecule and therefore only responds to one odorant
False
Each olfactory receptors cell expresses only a single receptor molecule type, but responds to a range of odorants
Where do olfactory receptor axons pass
Through the cribriform plate to the olfactory bulb
What do olfactory receptor axons excite at the olfactory bulb
Mortal cells and tufted cells in the olfactory glomeruli
Afferents from olfactory receptors cells, expressing a particular receptor molecule, selectively converge on just to glomeruli in each bulb
Which are bigger in size:
Mortal cells or tufted cells in the olfactory glomeruli
Mitral > tufted cells
Does lateral inhibition exist in the olfactory bulb
Yes- Peri glomerular cells and granule cells make reciprocal dendro-dendritic synapses with mitral cells
What is the point of lateral inhibition in the olfactory bulb
Sharpens mitral cell odour tuning
What patterns do different odours make in the olfactory bulb
Different odorant invoke distinct but overlapping activity patterns in the bulb
How do mitral cell axons leave the bulb
In the lateral olfactory tract
What does the anterior olfactory nucleus mediate
Mediates Inhibition between 2 bulbs via the anterior commissure
Where does the lateral olfactory tract synapse
On neurons in 5 regions of olfactory cortex:
Anterior olfactory nucleus Olfactory tubercle Pyriform cortex Amygdala Entorhinal cortex
Where does the olfactory tubercle projects to?
Where does this in turn project to?
The medial dorsal nucleus of the thalamus
The orbitofrontal cortex
What does the orbitofrontal cortex do
Mediates the conscious perception of odour
What does the pyriform cortex project to
The other olfactory cortical regions
Which of the regions that the lateral olfactory tract synapses with form part of the limbic system
What are they involved in
The amygdala and entorhinal cortex
The affective component of odour perception, mediating emotional and autonomic responses
How does odour specificity change throughout the olfactory pathway
At higher levels, cells become progressively more odour specific
Eg The majority of cells in the bulb respond to many odorants while those in the orbitofrontal cortex respond to just 1 or 2
What mediates response to pheromones
Where does it project to
The vomeronasal organ
Projects via the accessory olfactory bulb to the amygdala
