Chapter 6.2: ODOUR Remote Sensing

Question 1

the ___ ___ contains odour receptors

Answer 1

the olfactory epithelium

Question 2

olfactory sensory neurons stick to the ___ layer of the epithelium

Answer 2

MUCUS

Question 3

odourants are ferried through the mucus to olfactory sensory neurons by ___ ___ ___

Answer 3

odourant binding proteins

Question 4

olfactory receptors on olfactory sensory neurons are ____

Answer 4

GPCRs

Question 5

each olfactory receptor responds to a specific ____ on an odourant

Answer 5

epitope

Question 6

why does a specific smell trigger multiple odourant receptor types?

Answer 6

although olfactory GPCR receptors are epitope specific, odourants typically have multiple epitope types, activating multiple receptors

Question 7

Outline the olfactory transduction cascade

Answer 7

1) binding of odourant onto GPCR olfactory receptor activates GOLF G protein.
2) GOLF activates adenylyl cyclase which produces cAMP
3) caMP opens Na+ and Ca2+ channels, allowing cation influx. Cl- efflux also occurs
4) depolarization of olfactory sensory neuron occurs, and the AP is sent to the olfactory bulb.

Question 8

When an olfactory sensory neuron depolarizes, the signal is propagated to the ___ ___

Answer 8

olfactory bulb

Question 9

Main difference in G protein pathways between light and olfaction systems

Answer 9

light transduction uses transducin G protein
oldfactory transduction uses golf G protein

activating olfactory receptor opens Na+ and Ca2+ channels and causes depolarization

light activation of rod cells closes channels and triggers membrane hyperpolarization of bipolar cells.

Question 10

discrimination of odour occurs based on :

This is called a ___ ___

Answer 10

which olfactory neurons are activated. based on a combination scheme since different odourants has dif properties that activate dif types of neurons at once.

Question 11

sensory neurons expressing the __ ___ of receptor are ____ across the olfactory epithelium, but the axons converge onto a few ____ in the ___ ___ .

Answer 11

sensory neurons expressing the SAME TYPE of receptor are SPREAD across the olfactory epithelium, but the axons converge onto a few GLOMERULI in the OLFACTORY BULB

Question 12

sensory olfactory neurons “sort out” their axons in the ___ by:

Answer 12

sort their axons in the olfactory bulb by organizing their inputs onto a few glomeruli based on similarity.

Question 13

Chemotopy

Answer 13

mapping between odourant structure and spatial location of activated glomerli in the olfactory bulb. Dif odours activate distinct, although overlapping subsets of the olfactory glomeruli.

Odourants of similar chemical structure activate similar regions of bulb.

Question 14

Chemically, how are odourants discriminated?

Answer 14

odourants are discriminated based on number of carbon molecules in the carbon backbone, which discerns which area of the bulb they will put their inputs.

Question 15

sensory neurons project onto olfactory bulb’s ____, which have synapses with ___ cells; the large neurons in the olfactory bulb that project into the ___ ___

Answer 15

sensory neurons project onto olfactory bulb’s GLOMERULI, which have synapses with MITRAL cells; the large neurons in the olfactory bulb that project to the OLFACTORY CORTEX

Question 16

granule cells use ___ ___ synapses to make connections with mitral cells. How does this work?

Answer 16

reciprocal dendritic synapses between granule cells and mitral cells.

they have one excitatory and one inhibitory synapselocated right next to each other.

mitral cell releases glutamate onto granule cell, exciting the granule cell, and the granule cell then releases GABA ontot he mitral cell. This allows the mitral cell to be shut off shortly after its turned on.

Question 17

How do reciprocal synapses between mitral and granule cells in the olfactory bulb provide feedback inhibition?

Answer 17

mitral excited granule cells secrete GABA and inhibit surrounding mitral cells. the Stronger-firing mitral cell inhibit the weaker mitral cells aroun it. Narrows the range of odourants to which a mitral cell responds and keeps the average firing rate of mitral cells at a low even if the air is filled with odourants, you’re only going to be smelling the STRONGEST one that is eliciting the most firing mitral cells. prevents you from getting overwhelmed.