Week 2 Olfaction

Question 1

Olfactory system smelling process

Answer 1

Odorant in air - inhales/sniffs- odorant in nasal cavity.
The odorants make their way up the nose to the olfactory mucosa - this is a mucus membrane, the lining at the back of the nasal cavity that is covered in a layer of mucus. The odorant become temporarily trapped once they reach the epithelium

Question 2

Part 2: of smelling process

Answer 2

Odorant reaches olfactory epithelium - covers in mucus membrane
Signal transduction occurs because olfactory receptor neurons (ORN) tht project cilia (little hairs) into the mucus membrane of the olfactory epithelium
Any odorant particles binds to the protein on the cilia of the ORN

Question 3

Olfactory epithelium contains 3 cells

Answer 3

1. Basil cell

2. Receptor cell 3. Supporting cell

Question 4

Signal transduction in olfaction

Answer 4

Odorant molecule binds to and activates an odorant receptor on the ORN, this initiates an electrical signal in the ORN
- One tye of receptor per ORN but this can bind multiple types of odorant
- 350 types of ORN
Each odorant ahs aunique ORN recognition pattern

Question 5

Loss of smell

Answer 5

Not due to loss of olfactory receptor neurons Instead due to transient depletion of their odorant binding proteins.
The cells stop expressing these odorant binding proteins so they can no detect odorants that are in the mucus membrane which results in partial or full loss of smell

Question 6

olfactory pathway

Answer 6

Axons from ORNs project through bone cavities in skull and synapse with mitral cells in the olfactory bulb
Glomeruli - clusters of the nerve endings mitra cells project axons into the brain that synapse with neurons in olfactory cortex ORN sends axons through little holes in the skull and the axoms project onto the mitrals in the olfactory bulb - 1st synapse in the olfactory pathway: make contact with the dendrites of the mitral cells of the olfactory bulb forming dense clusters of nerve endings. The mitral cells project higher up into the brain to the olfactory cortex

Question 7

synaptic pathway

Answer 7

ORN - mitra cell - olfactory cortical neuron

Question 8

Different populations of cells activate at each

step, pathway

Answer 8

1. Recognition pattern across ORNs
2. Unique pattern across the mitral
   cells all type A ORNs synapse onto type A mitral cells … all type B ORNs onto a type B mitra cell etc
3. Activates a specific pattern of olfactory cortical neurons

Question 9

Amygdala:

Answer 9

emotion

Question 10

Hippocampal formation

Answer 10

memory

Question 11

Thalamus

Answer 11

relay to/from other areas, attention

Question 12

Orbitofrontal cortex (OFC)

Answer 12

emotion recognition, behavioural inhibition, hedonic assessment, decision making, taste

Question 13

Odour memories

Answer 13

= emotional, autobiographical memories evoked by an odour.

An example of the proust effect(the vivid reliving of events from the past through sensory stimuli)

Question 14

Body odour disgust scale

Answer 14

individuals’ differences in disgust reaction to a variety of body odours.

Question 15

olfactory bulb: infants

Answer 15

Nature has a role
Infants respond positively to pleasant smells and negatively to unpleasant smells
In utero exposure alters olfactory bulb development
What the baby is exposed to during pregnancy will affect the development of of the olfactory bulb

Question 16

Function of olfactory

Answer 16

1. Detection
2. Identification
3. communication

Question 17

Detection of environment cues

Answer 17

ambient scenting: marketing tool used by supermarkets, real estate agents and many more - make the house smell like baking and will help the house sell because they enjoy being there and makes it feel homely
Skunk water: malodorant used by military/law enforcement to disperse crowds

Question 18

Identification of environmental cues

Answer 18

Humans can discriminate more than 1 trillion olfactory stimuli

Question 19

Communication of environment cues

Answer 19

Mammals including u send and receive odour messages
-defence mechanisms
Territory marking
Emotional state
Sex-realted
disease /immune status
All highly influenced by choice and thus under heavy control by context, mood,attention, memory etc - top down processing

Question 20

Pheromone signalling

Answer 20

Thought to involve the vomeronasal organ Part of the accessory olfactory system
An anatomic mystery - although first discovered in humans, man believe we don’t even have them - we do but they might shrink or get lost as we get older

Question 21

The vomeronsal organ

Answer 21

Located in the anteroinferior of the nasal - the bridge between the nose and nostril. Enriched in pheromone receptor cells.
Send projections (nerve 0) to the accessory olfactory bulb (aka vomeronasal bulb). - no evidence it is in humans
From there to amygdala and hypothalamus (release of hormones)

Question 22

Pheromone receptor cells

Answer 22

Detect non-volatile chemical cues( i.e chemicals that don’t vaporise easily). Requires direct physical contact with the source of odorant (think animals using scent rubbing)
No evidence of functional pheromone receptor cells in adult humans

Question 23

Are the pheromone companies lying to us

Answer 23

Well maybe…
Pheromones do affect mate selection in humans but candidate human pheromones all seem to have receptors in the olfactory mucosa, not the VNO (vomeronasal organ)

Question 24

Four reasons odour discrimiantion experiments are difficult

Answer 24

1. Chemicals can change odour depending on physical structure isomers ; same chemical constitution but mirror images
   The higher concentration the more unpleasant
2. Concentration dependents changes in odour
   Sor many smells, high concentration = unpleasant
3. Individual differences(physical,cultural, psychological)
   Odour ID = semantic recall(memory, language issues)
   culture/exposure will play a role
   Role of language very important - often difficult to describe sometimes lacking consistent terminology
   mood , attention, wakefulness, motivation Biology
4. Ecological validty
   Experimenter present odours one by one (usually)
   Relfeclt of real life
   Typically we arent exposed to odours in isolation
   Much easier to identify smells when you can also see what your smelling