Lecture 16: Smell lecture 2 Flashcards

1
Q

Describe the olfactory bulb projections;

A
ORNS
(Olfactory nerve 1)
Olfactory bulb
(Lateral Olfactory tract)
Olfactory bulb targets;
- Pyriform cortex
- Olfactory tubercle
- Amygdala
- Entorhinal cortex
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2
Q

Describe the projections from the olfactory primary targets

A
  • Pyriform cortex
  • Olfactory tubercle
  • Amygdala
  • Entorhinal cortex

All innervate the

  • Hypothalamus
  • Thalamus
  • Orbitofrontal cortex

The entorhinal cortex especially innervates the Hippocampus

The Pyriform cortex especially innervates the
orbitofrontal cortex.

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3
Q

Whats the importance of the entorhinal cortex?

A

Provides major sensory input into the hippocampus, also receives direct sensory input from olfactory regions

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4
Q

Whats the importance of the limbic system?

A

A group of neural structures which includes;

  • Pyriform cortex
  • Olfactory tubercle
  • Amygdala
  • Entorhinal cortex

Involved in many aspects of memory and emotions

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5
Q

How is the olfactory sense unique among the system?

A

B/c of its direct and intimate contact with the limbic system

explains why smell has strong emotional associations

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6
Q

What does a functional MRI shown in terms of brain activity to smell?

A

Different parts of the brain detect pleasant (orbitofrontal cortex) and unpleasant odours (Cingulate cortex)

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7
Q

What are the theories of olfactory perception?

A

Vibrational Theory

Shape-pattern theory

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8
Q

What is the vibrational theory;

A

Every perceived molecule has a vibrational frequency, molecules that have the same vibrational Hz will smell the same.

old theory

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9
Q

What is the shape pattern theory;

A

(dominant biochem theory)

Different scents activate different arrays of ORNs in the olfactory epithelium

A combination of receptor activation is responsible for a given smell

Various arrays produce specific firing patterns of neurons in olfactory bulb which determine the scent we perceive.

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10
Q

Describe the shape pattern theory in terms of receptors;

A

A odorant can bind the receptor binding site and produce a response, but the intensity of the response will depends on the ‘pattern” matching of receptor-odorant

i.e needs same shape and colour (receptor and odourant), not just shape.

correct shape-pattern = best response

Give rise to odotopic mapping

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11
Q

Describe odotopic mapping using shape-pattern theory

A

In the olfactory bulb there is shape mapping (same) in the longitudinal plane and pattern mapping (same) in the transverse.

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12
Q

Why is the shape pattern theory good?

A

Explains why we can detect many odours with only 400 genes.

We can detect a pattern of activity across receptors.

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13
Q

How does intensity influence receptor activation?

A

Intensity of odorant changes which receptors will be activated

Weak concentrations of odourants will not smell the same as strong concentrations

Therefore specific time order of ORN activation is important

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14
Q

Whats a complication of odour detection?

A

We rarely smell pure odours, usually mixtures

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15
Q

How do process the components in odorants mixture?

A

Olfaction is primarily a synthetic sense; but some analytic properties can develop

synthesis; i.e red + green makes yellow light, but in yellow light we cannot detect red or green

Analysis: High and low notes can be played together but we can detect individual notes

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16
Q

How does the visual system influence olfaction?

A

The visual system can change the perception of a smell

17
Q

Describe olfactory psychophysics;

A

There must be substantial cognitive function for detection, recognition and discrimination of smell

18
Q

How much stimulation is required before we can perceive a smell to be there?

A

Olfactory detection thresholds depend on several factors including age, gender and training.

Women generally lower thresholds than men
by 65 generally 60% population are anosmic
Professional wine tasters can distinguish up to 100,000 odours.

19
Q

How can we measure sense of smell?

A

Most common method is a 40 item scratch and sniff

Use a cards and assess how many are correctly identified (options given)

However does not indicate perception threshold

20
Q

How do we measure detection threshold for a specific odour?

A

Staircase method

Method for determining the concentration of a stimulus for detection at a threshold level

21
Q

Describe the staircase method;

A
  • Stimulus is presented at increaseing concentrations until detection is indicate, concentrations are then decreased until detection ceases.

This is repeated several times an the average reversal point is threshold

22
Q

What is another method for determining threshold concentration?

A

Triangle test; Participant is given three odours, two of which are the same.

Must identify the odd one

The order of the three is varied to increase accuracy

23
Q

What is adaptation in relation to smell?

A

After continuous exposure to the odourant the receptors adapt and detection ceases.

This process is called desensitization (reversible)

I.e cant smell your own perfume

Sense of smell is typically a change detector.

24
Q

What is receptor cross adaptation?

A

The reduction in detection of an odourant following exposure to another odourant

assumed to occur because odourants share one or more ORN in their transduction

25
Q

How does attention influence conscious perception of odours?

A
  • Attention increases your ability to detect odours

- Attention is cut off during sleep, so is our ability to respond to odours

26
Q

What is olfactory hedonics?

A

Liking a smell or not

27
Q

How is olfactory hedonics created?

A

Typically measured with scales pertaining; pleasantness, familiarity, intensity

Therefore we tend to like odours we have smelled many times before

28
Q

Describe relationship between intensity and pleasantness of smell;

A

Complex relationship.

Hardly ever a linear relationship

Very hard to predict pleasantness based on structure or intensity

29
Q

What are odour induce recollections associated with?

A

odour induced recollections are strongly emotional

30
Q

What causes the strong association with olfaction, memory and emotion?

A
  • Neuroanatomical and evolutionary connections between odours and emotion
  • Olfaction is processed in the orbitofrontal cortex, hedonic judgement also occurs here thus explaining the increased emotionality of smells.
31
Q

Describe aromatherapy;

A

The use of smells to alter mood, performance, well being

Physiological alters HR, BP and sleep

32
Q

What are some olfactory disorders?

A
Anosmia
Partial anosmia (loss of certain smells)
hyposmia 
parosmia
phantosmia
33
Q

What is parosmia?

A

All smells are perceived as unpleasant

34
Q

What is phantosmia?

A

unlpeasant smell helucinations

35
Q

What are the causes of smell disorders?

A
Genetic ; Kallmans syndrome
Toxins ; petrol
Post Viral ; URT infection
Drugs; Chemotherapy
Neurodegenerative disease; Parkinsons
Head Trauma
Autoimmune disease
Inflammation; Chronic rhinosinuitis
36
Q

What is a commercial application of olfactory research?

A

Electronic nose technology

37
Q

What is electronic nose technology?

A

Devices that can detect simple or complex smells through sensors

38
Q

What is the application of electronic nose technology?

A

Medicine - detection of acetone on diabetic breath, also smells related to RTI, UTI, GI infections i.e TB, H. pylori, renal failure, cancer

non-medical
- food spoilage, food classification (beer, wine, coffee)