Olfaction Flashcards
What is olfaction?
detection of chemicals in the air
What is gustation?
detection of chemicals that have been placed in the mouth
The olfactory system detects _______________ that bind to _________________ receptors (_____________)
odorants; olfactory; in the nose
The gustatory system detects _______________ that bind to _________________ receptors (_____________)
tastants; gustatory; tongue
TRUE or FALSE: olfactory system detects volatile substances wherease the gustatory system detects water soluble substances
TRUE
TRUE or FALSE: all vertebrates have an accessory olfactory system
FALSE: all vertebrates have a MAIN olfactory system; MOST LAND vertebrates have an accessory olfactory system
another name for an accessoryt olfactory system
vomeronasal system
Where does the main olfactory epithelium (MOE) project to? vomeronasal organ (VNO)?
- MOE to main olfactory bulb (MOB)
- VNO to accessory olfactory bulb (AOB)
TRUE or FALSE: the olfactory epithelium is just a flat surface
FALSE: labyrinth-like
Place the following in order of info transmission:
- olfactory epithelium
- cribiform plate
- olfactory bulb
- nasal cavity
nasal cavity, olfactory epithelium, cribiform plate, olfactory bulb
Describe the cribiform plate
sieve-like structure between the anterior cranial fossa and the nasal cavity; part of ethmoid bone
TRUE or FALSE: the olfactory epithelium has a small surface area
FALSE: large surface area
how much larger is the olfactory epithelium surface area in dogs vs humans
30x larger in dogs
TRUE or FALSE: dogs have more olfactory receptors than humans
TRUE
What is the lifetime of olfactory receptors? is this considred short or long?
60 days; short
How many receptors are made daily?
10,000-30,000
What kind of cells doe new olfactory receptors arise from?
basal cells (stem cells)
Which type of olfactory cells does COVID affect?
basal cells
Describe the path of information transmision from the dendrites of the olfactory recetpors to the brain (OR = olfactory receptor)
OR dendritic knobs –> OR unmyelinated axons –> synapse on mitral cells at the glomerulus in the olfactory bulb –> mitral cell axons go to the brain
how many cilia do the dendritic knobs of the OR have?
20-30
what is the diameter of the OR axons?
0.2 micrometer
describe the afferent and efferent path of information transmission in the olfactory system using the following:
- granule cell
- olfactory tract
- centrifugal afferents
- mitral cell
- periglomerular cell
- tufted cell
- glomerulus
- OR
- efferent: OR –> periglomerular cells in the glomerulus –> tufted and mitral cells –> olfactory tracts
- afferent: centrifugal afferents –> granule cells –> mitral and tufted cells
How do odorant molecules bind to the OR?
odorant molecules dissove in the mucous then interact with ODROANT BINDING PROTEINS in the mucous; then this complex binds with OR receptors on the cilia
What percentage of the genome is dedicated to olfaction?
3%
Describe the structure of all OR proteins.
- 7 transmembrane segments
- GPCR
- cAMP second messenger
At which transmembrane segments of the OR proteins do odorants bind?
3,4,5
TRUE or FALSE: each OR neuron expresses multiple types of OR proteins
FALSE: each OR neuron expresses ONE type of OR protein
What reflects the range of scents that an organism can detect?
number of OR genes
TRUE or FALSE: primates have many OR genes
FALSE: very few OR genes
TRUE or FALSE: rodents have 4x the number of OR genes than primates
TRUE
Arrange the following form most OR genes to least: primates, rats, african elephatns
african elephant > rat > primate
Which ions do odorant binding conduct?
initial inward K+ current and then larger longer inward current due to 2nd messenger system (Na+, Cl-, Ca2+)
TRUE or FALSE: the odorant binding directly opens the ion channel
FALSE: 2nd messenger system is involved
Draw the current resulting from odorants released onto OR neuron cell body. onto the cilia?
slide 13; A then B
Describe the 2nd messenger cascade that results from odorant binding.
- odorant binds to OR protein –> GDP exchanged for GTP causing alpha-subunit to separate from G-protein
- GTP-alpha-subunit activates adenylyl cyclase (AC) –> ATP converted to cAMP
- cAMP opens cyclic-nucleotide gated cation channel
- depolarization results from Na+ (and Ca2+) influx
- Ca2+ influx cause Cl- channels to open; Cl- flows OUT of cell to maintain depolarization
Why does Cl- have to flow out of the OR cell to maintain depolarization?
the outside of the cell is not an extracellular space, but instead it is air or mucous; therefore the Na+ levels are not normal and do not allow Na+ to keep flowing in as in usual depolarizations. Cl- flowing out of the cell gives an extra push for depolarization to occur.
How would the olfactory system be affected if we lacked cAMP-gated channels?
no odour discrimination
What is different about the second messenger system in invertebrates?
- OR proteins may be coupled to G proteins that activate PLC
- IP3 can act on Ca2+ channels directly
Which zones of the olfactory epithelilum and olfactory bulb are different families of the OR proteins localized to?
4 and 5
There is segregation/refinement of information from each OR protein type. How is this demonstrated?
each glomerulus receives input from ORs containing a SINGLE OR PROTEIN
What kind of map is found in the olfactory bulb?
chemotopic (slide 19)
TRUE or FALSE: each OR protein responds to a unique odor
FALSE: each OR protein can recognize more than one odorant (odour generalist receptors)
If each OR protein can recognize more than one odorant, then what determines the smell that we detect?
pattern of activity across all receptors / POPULATION CODING
TRUE or FALSE: one odorant can excite more than one OR neuron
TRUE
How many unique odours are there?
10,000
What is the function of the vomeronasal organ?
detecting pheromones
What are pheromones?
chemical signals that affect behaviour or physiology in conspecifics
How does the olfactory system react to pheromones in mammals? in snakes and lizards?
- mammals: nasopalatine duct is normally closed, but opens when an odour associated with a pheromone is detected
- snakes and lizards: tongue draws in pheromones into the vomeronasal organ (tongue flicking)
What is the name for the response where arnimals curl the tongue and open the mouth to allow scents to enter the VNO?
Flehmen response
What is the only difference between the olfactory epithelium and the vomeronasal epithelium?
- vomeronasal epithelium has microvilli
- olfactory epithelium has cilia
How many vomeronasal receptor (VR) proteins are there in mice? how specific are they?
- 300 different VR proteins in mice
- each responsive to a single (or a few) specific chemical compounds
what is the difference between VR and OR?
- VR = odour specialist receptors
- OR = odour generalist receptors
What are the 2 main families of G proteins that VRs are coupled to? Describe the cascade. which domain is important in this cascade?
- V1R coupled to Gi2
- V2R coupled to Go
- both use IP3 and DAG as 2nd messengers to open TRPC2 cation channels; Na and Ca both flow in; Ca binds to CaM (CIRB domain)
Where do vomeronasal receptor cells project to?
accessory olfactory bulb
TRUE or FALSE: the vomeronasal epithelium projection to the accessory olfactory bulb has a similar type of organization to olfactory epithelium projection to olfactory bulb
TRUE
TRUE or FALSE: the main olfactory bulb projects to the thalamus
FALSE: NO RELAY TO THALAMUS
List the projections of the main olfactory bulb. Which is considered the primary olfactory cortex?
(REMOVE SLIDE)???
- anterior olfactory nucleus (AON)
- tenia tecta (TT)
- olfactory tubercule (OT)
- piriform cortex (PC) –> like primary olfactory cortex
- anterior nuclsie of the cortical amygdala (COA) to entorhinal cortex (EC)
What is the lateral olfactory tract?
main olfactory bulb –> COA –> EC
What are the main projections of the main olfactory bulb? what are their functions?
- piriform cortex: identification of odours
- amygdala: emotion/fear/aggression
- entorhinal cortex and hippocampus: memory
- hypothalamus: appetite control/sexual behaviour
The main olfactory bulb synapses onto the _____________ amygdala. The accessory olfactory bulb synapses onto the ___________ amygdala.
- main = lateral (aLA, pLA)
- accessory = medial (aMA, pMA)
TRUE or FALSE: the lateral amygdala has more extensive connections with the hypothalamus; this means that the main olfactory bulb has more connections with the hypothalamus
FALSE: medial; accessory
Which nucleus has extensive connectsion with the amygdala and hypothalamus? Is it associated with the main or accessory olfactory bulb?
- bed nucleus of the stria terminalis (BST)
- accessory olfactory bulb
