Physiology: smell Flashcards
Overview of smell
SIGNAL
What is the name of the signal?
Odorants
SIGNAL
What 2 aspects of the nose help odorants come into contact with olfactory cells?
Turbinates: help create turbulent flow –> odorants more likely to bump into olfactory cells
The nose is highly vascularised - warms incoming air, increasing speed of odorant particles
PERIPHERAL RECEPTORS
What is the name of the receptors?
Olfactory cells
PERIPHERAL RECEPTORS
Olfactory epithelium
- What are the 3 cell types of the olfactory epithelium?
Olfactory cells (neurons)
Supporting cells (pseudostratified columnar epithelium)
Basal cells (stem cells)
PERIPHERAL RECEPTORS
Olfactory epithelium
- Can basal cells renew both olfactory cells and supporting cells?
- What is unique about this?
Yes
Means olfactory cells are one of the few neuronal populations which are capable of regenerating
PERIPHERAL RECEPTORS
Olfactory epithelium
- Where is the olfactory epithelium found?
- Lining the nose
- Lining the mouth (surface of hard palate, pharynx)
PERIPHERAL RECEPTORS
Olfactory cells
- Are they first order neurons?
- Structurally, what class of neurons are they?
Yes
Bipolar neurons
PERIPHERAL RECEPTORS
Olfactory cells: apical pole
- What structures enable them to interact with odorants?
Dendrites reach towards surface of olfactory epithelium
At the surface, has olfactory cilia - which have olfactory receptor proteins on them, which bind to odorants
PERIHPERAL RECEPTORS
Olfactory cells: basal pole
- Describe the unique grouping of axons
- Describe how the axons reach the olfactory bulb
Axons expressing the same odorant receptor protein cluster in bundles
Axon bundles pierce the cribiform plate of the ethmoid bone, to synapse in the glomeruli of the olfactory bulb
PERIPHERAL RECEPTORS
Olfactory receptor proteins
- Where are they found?
- What class of receptors are there?
- Are there more olfactory receptor protein genes than there are proteins expressed? Why?
On olfactory cilia, of olfactory cells
GPCRs
Yes (1000 vs 350) - may indicate that our sense of smell has become less important over evolutionary history
PERIPHERAL RECEPTORS
Olfactory receptor proteins
- What part of olfactory receptor proteins do odorants bind to?
- Do only certain families of odorants bind here?
- What allows us to perceive the unique smell of each odorant?
Odorant binding pockets
Yes
The activation of unique combinations of olfactory receptor proteins
PERIPHERAL RECEPTORS
Signal transduction
- Describe the signal transduction pathway
- If components of this pathwy are not functional, can animals become anosmic?
Yes
AFFERENT PATHWAYS
The olfactory bulb
- Are different classes of odorants coded in the olfactory bulb (atleast, in animal studies)? Why?
Yes
As each neuron expressing a particular receptor will project its axons to a specific glomerulus within the olfactory bulb
AFFERENT PATHWAYS
What are the names of the 2 second order neurons?
Mitral cells
Tufted cells
AFFERENT PATHWAYS
Mitral cells
- Where are their dendrites located?
- What structure do their axons form?
- Where does this structure project to?
In the glomeruli of the olfactory bulb
Olfactory tract (CN I)
The primary olfactory cortex
CENTRAL PROCESSING
What is the primary cortex called?
What is another name for it?
Where is it locatd?
Primary olfactory cortex, aka the piriform cortex
Between the frontal and temporal lobes
CENTRAL PROCESSING
- Describe the pathways olfactory information can go from the primary olfactory cortex
- Why is smell strongly associated with long term memory?
As smell is often processed in the hippocampus
DISRUPTION
Names for
- Lack of odor detection?
- Reduced odor detection?
- Distorded odor detection?
Can it have a strong impact on QoL (eg. anxiety and depression)?
When can it be life threatening?
Anosmia, hyposmia, dysosmia
Yes
When unable to detect harmful smells - smoke, gas, toxic chemicals
DISRUPTION
Describe the effect of smell on taste, with an example
When olfaction is impaired, taste is impacted. (Eg. block nose, can’t tell the difference between milk and dark chocolate)
Thus, most disorders of taste are actually olfactory in origin
DISRUPTION
Describe the effect of smell on taste, with an example
When olfaction is impaired, taste is impacted. (Eg. block nose, can’t tell the difference between milk and dark chocolate)
Thus, most disorders of taste are actually olfactory in origin
