olfaction

Question 1

odourant binding

Answer 1

odourant into nose → caught in mucus → binds to olfactory receptor on cilia of odourant receptor neuron (ORN)

Question 2

odourant signal transduction

Answer 2

binding to olfactory receptor on odourant receptor neuron → triggers depolarisation → olfactory bulb → AP in olfactory nerve (cranial nerve I) neuron

Question 3

odourant signal to brain

Answer 3

olfactory nerve (cranial nerve I) neuron → to primary olfactory cortex → then projects to OFC, thalamus, amygdala and hippocampus

Question 4

odourant cortical processing/projections

Answer 4

• primary olfactory cortex = piriform cortex
• PC projects to lots of other brain regions
  
  • amygdala ⇒ emotion
  • hippocampus ⇒ memory
  • thalamus ⇒ relay to/from other areas, attention
  • orbitofrontal cortex (OFC) ⇒ emotion recognition, behavioural inhibition, hedonic assessment, decision making, taste

Question 5

specificity in odourant detection

Answer 5

• there is 1 type of receptor per ORN but this can bind to multiple types of odourant
• ~350 different types of ORNs
• Each odourant has a unique ‘ORN recognition pattern’
• A population code emerges at every level!

Question 6

Hyposmia

Answer 6

reduced ability to detect smells (e.g. when sick)

Question 7

Anosmia

Answer 7

complete inability to detect smell. In rare cases a person might be born with a condition called congenital anosmia

Question 8

Parosmia

Answer 8

a change in the normal perception of smell (something that once smelled good now smells unpleasant (due to an infection or trauma)

Question 9

Phantosmia

Answer 9

• Sensation of an odour that isn’t there! (hallucinating a smell, not usually pleasant)
  
  • could be problems in nose, passage, or brain (e.g. tumor)

Question 10

retronasal olfaction

Answer 10

food particles from mouth enter nose → bind & produce smell sensations that are associated with the taste or flavour

Question 11

2 pathways of odourants to brain

Answer 11

• nostrils to POC → smell
• top of throat to gustatory cortex → taste

Question 12

interaction between smell and taste

Answer 12

• retronasal
• info both gustatory and olfactory cortices
• OFC receives info from gustatory and olfactory cortexes ⇒ integration of informatio

Question 13

how many different olfactory stimuli can we discriminate?

Answer 13

can detect and discriminate > 1 trillion olfactory stimuli

Question 14

factors that may influence an individual’s ability to detect or identify a certain odour

Answer 14

• genetic: number of receptors, sensitivity
• past experience/memory
• age, sex
• health
• nose anatomy

Question 15

function of yummy baby smell

Answer 15

• activates reward circuitry in adult brain
• reminds us to look after our baby

Question 16

armpit smell

Answer 16

• not volatile compounds (like in off food)
• 3 key components: thiols, steroids and diverse set of acids
• converted to smell compounds by microbes on our body
• people with lots of Corynebacterium, common in men = more smelly
• men also make more of the precursors = stinkier

Question 17

chemically-mediated emotional reactivity and contagion

Answer 17

• reactivity: smelling someone’s anxiety can promote empathy
• contagion: smelling happiness can produce feel good chemicals in others

Question 18

olfactory signals re immune system

Answer 18

• we can detect via sweat when someone’s immune system is ramped up, and our own leaps into action
• can learn to identify particular diseases by smell from specific smells given off in urine, sweat, breath, faeces

Question 19

approach and avoidance behaviour

Answer 19

• approach: bonding
• incest avoidance: parents dislike the smell of their opposite sex kids once they hit puberty

Question 20

lexicon for smell

Answer 20

• we lack the words to describe many specific scents, compared to Umpilla (aboriginal Australian hunter gatherer language)
• less words = less appreciation and awareness for smell
• but also language reflects lower reliance on scent for communication

Question 21

pheromones

Answer 21

odourants that are detected unconsciously and can convey communication/affect behaviour
- distinction is functional, based on the response they promote in the person smelling them

Question 22

kin recognition

Answer 22

• mothers recognise or at least prefer the smell of their kids
• HLA (set of genes involved in immunity) play a role, prefer smell of people with diverse HLA, may drive sexual attraction

Question 23

odourants across the placenta

Answer 23

odour chemicals cross the placenta, baby attracted to smell of human milk, flavoured by mother’s diet