5. Olfaction Flashcards
the detection of chemicals in the air
olfaction
detects odorants that bind to olfactory receptors
olfactory system
detects tastants that bind to gustatory receptors
gustatory system
both the olfactory system and the gustatory system contribute to our perception of:
taste
do fish have an olfactory system?
yes
all vertebrates have a _____, and most land vertebrates have an _____
main olfactory system, accessory olfactory system (vomeronasal system)
the main olfactory epithelium (MOE) projects to the:
main olfactory bulb (MOB)
the vomeronasal organ (VNO) projects to the:
accessory olfactory bulb (AOB)
a sieve-like structure between the anterior cranial fossa and the nasal cavity (forms part of the ethmoid bone)
cribiform plate
where are the olfactory receptors located?
sensory cilia
how many sensory cilia does each dendritic knob have?
20-30
olfactory receptor cells project to:
mitral cells
site where dendrites of mitral cells interact with the axons of olfactory receptor cells
glomerulus
mitral cell axons project to the:
brain
what is the lifetime of olfactory receptor cells?
~60 cells
olfactory receptor cells arise from:
basal (stem) cells
odorant molecules dissolve in the mucous in the nasal cavity, interact with odorant binding proteins in the mucous, and then:
bind with olfactory receptors on the cilia
the binding of odorants to olfactory receptors leads to:
depolarization (and hopefully an action potential)
all olfactory proteins are composed of:
seven transmembrane segments (GPCRs)
what type of pathway do olfactory receptors activate?
GPCR pathway with cAMP as a second messenger
which segments of the olfactory receptor show considerable sequence variability?
segments 3, 4, and 5
which segments of the olfactory receptor do odorants bind to?
segments 3, 4, and 5
each olfactory receptor neuron expresses:
only one type of olfactory receptor protein
the number of olfactory receptor genes can reflect:
the range of scents detected
when the odorant is in a K+/Cl- solution the initial inward current is due to:
increased extracellular K+
does the odorant itself open the receptor channels?
no (it is a G-protein coupled mechanism)
list the five major steps of odorant opening ion channels via a GPCR mechanism?
1) odorant binds to the olfactory receptor protein (GDP exchanged for GTP causing the alpha-subunit to separate from the G-protein)
2) GTP alpa subunit activates adenylate cyclase and ATP is converted to cAMP
3) cAMP opens the cyclic-nucleotide gated cation channel
4) depolarization results from Na+ and Ca++ influx
5) Ca++ influx cause Cl- channels to open, Cl- flows out of the cell maintaining the depolarization
are transgenic mice lacking cAMP gated channels able to discriminate odours
no
some olfactory receptor proteins many be coupled to G-proteins that activate _____ instead of _____
phospholipase C (PLC), adenylate cyclase (AC)
by activating PLC pathways, IP3 can:
act on Ca++ channels directly
G-protein coupled olfactory receptors that utilize PLC are important in:
invertebrate olfaction (less so in vertebrates)
different families of olfactory receptor proteins are localized to:
4 or 5 zones in the olfactory epithelium and olfactory bulb
each olfactory zone contains ____ olfactory receptor proteins that are closely related
100-200
each glomerulus receives input from olfactory receptors containing:
a single olfactory receptor protein
true or false: there is a segregation of information from each olfactory receptor protein
true
it is suggested that the olfactory bulb is organized into a:
chemotopic map
true or false: olfactory receptor proteins respond to unique odours
false (each odorant protein can recognize more than one odorant)
how is smell determined?
by a pattern of activity across all olfactory receptors (population coding)
true or false: one odorant can excite more than one neuron
true
most land vertebrates have a vomeronasal organ specialized for:
detecting pheromones
chemicals released by an organism that cause a physiological and/or behavioural response in other individuals of the same species
pheromones
what is an example of a pheromone/vomeronasal system?
LH and testosterone are released when male mice/hamsters are exposed to chemosensory stimuli from females
in mammals, the nasopalatine duct is normally closed, but opens when:
an odour associated with a pheromone is detected
in snakes and lizards, the ____ draws pheromones into the vomeronasal organ
tongue
the curling and opening of the mouth that allows scents to enter the vomeronasal organ (VNO)
Flehman response
vomeronasal receptor neurons have _____ rather than _____
microvilli, cilia
is the vomeronasal epithelium organized similarly to the olfactory epithelium?
yes
what type of receptors are vomeronasal receptor proteins?
G-protein coupled receptors
there are as many as 300 different vomeronasal receptor proteins in mice which are each responsive to:
a single (or a few) specific chemical compounds (important for mating responses)
what are the two major families of vomeronasal receptor proteins?
- V1R (coupled to Gi)
- V2R (coupled to G0)
both V1R and V2R use IP3 and DAG as second messengers to open:
TRPC2 cation channels
the organization of the vomeronasal receptor cells projections to the accessory olfactory bulb is similar to:
the organization of olfactory epithelium projections to the olfactory bulb
olfactory bulbs project to the:
brain
where in the brain does the olfactory bulb project to?
the piriform cortex (PC) –> aka the olfactory cortex
where is the olfactory cortex located in humans?
deep in the medial part of the medial temporal lobe (bypasses the thalamus)
responsible for the identification of odours in the olfactory cortex
the piriform cortex (PC)
the lateral amygdala gets information from the:
main olfactory bulb
intimately linked with the hypothalamus (sexual behaviours, aggression, other social behaviours)
the medial amygdala
pheromones lead to:
hormones
the main olfactory bulb is associated with the _____, and the accessory olfactory bulb is associated with the ______
lateral amygdala, medial amygdala
the bed nucleus of the stria terminalis (BST), extensive connections with the:
amygdala and hypothalamus
