Physiology of smell - Olfactory System Flashcards
What type of receptors are for taste and smell?
Chemoreceptors
What can taste and to a lesser extent smell regulate?
GI secretions
Olfactory bulb
What is the messenger system used in olfaction?
G-protein second messenger system
What are the 7 primary qualities of smell?
Peppermint
Musk
Floral
Ethereal
Pungent
Putrid
Comphoraceous
What are the second order sensory neurons?
Mitral cells
Olfactory bulb
does not pass through the thalamus
What do bi-directional projections give rise to?
Smell localisation
Where do olfactory pathways from the nose project to?
The cortex
When the receptor on cilia is activated, how is the calcium channel opened?
Via a GPCR, activates adenalate cyclase
activates cAMP, which open the calcium channel
What is the effect of Ca coming into the nerve?
Cause an AP, and depolarisation
activates chloride channels, Cl- moves out of the cell
What is the negative feedback system of Ca2+?
Activates calmldulin,
- inhibition of cAMP on the Ca2+ channel
- caMK, inhibit AC
What glamerulae are most highly activated?
Red and green
lateral inhibition
What are the zones of the olfactory epithelium?
Zone I to IV in the olfactory bulb
What does the vomeronasal organ detect?
Pheromones
How does the vomeronasal organ connect to the olfactory bulb?
Anterior to the posterior olfactory bulb
Does the vomeronasal organ signal to the olfactory in a gradient?
Yes
Do humans have a vomeronasal organ?
Likely no
What is the competition model?
olfactory neurons are the only neurons in the CNS which can regenerate.
a) the inactive neurons were competed out as they could not bind ligand.
b) neurons not competed out, as the neurons were exposed to a ligand they could both not detect
What are olfactory sheathing cells?
Sheathing cells can support regeneration of olfactory bulb neurons
Could regenerate CNS
Where do the olfactory receptor neurons project their axons?
through the cribriform plate and into the olfactory bulb
What do the olfactory neurons/axons synapse onto in the olfactory bulb?
second order neurons, called mitral cells
What is the role of the mitral cells?
send their olfactory neurons down the olfactory tract to the olfactory cortex
What happens when the depolarisation threshold is reached in the cilia?
signal transduced to the olfactory cortex
How many types of receptor do each olfactory neurons express?
only 1 type of receptor
What happens when the axons reach the mitral cells?
they begin to branch = ready for synapse
What is a glomerulus?
where the axonal branches and dendrites are synapsing together
What do they colours represent in this image?
the neurons which are expressing the same type of receptor
Do the grey and pink neurons synapse with the same glomerulus (same mitral cells)?
no, as they express different receptors. the neurons synapse with specific mitral cells for their receptor creating a specific response
there must be axon guidance
When can mitral cells inhibit one another?
if they are strongly activated
What are the inhibitory cells? (of mitral cells)
granular and perigomerular cells
block out other background smells
What do you call the inhibition of background smells to allow us to pick up stronger scents?
sharpening the odour code
How is topography achieved in the olfactory system?
The temporal axons have many receptors for the ligand so are inhibited, don’t stretch far into the tectum and are inhibited
nasal axons, from other side of retina (nose), have less receptor for inhibitory ligands.
they can project their axons much further before hey are inhibited.
How do we flip the image the right way round again?
The concentration of receptor for inhibitory ligand is on a gradient. the neurons gets flipped and is does the image
