Lecture 2: taste and smell Flashcards
What are taste and smell?
Chemical compounds
Outline Wedekind 1995
*dirty t shirts
Outline McCulloch et al 2006
*dogs can pick up diseases in people through their sense of smell
How do we recognise smell?
- combination receptor code
- each odour has a different spatial pattern
How does adaptation to recognising smells work?
Receptors stop firing as much if repeatedly exposed
How does adaptation to recognising smells work?
Receptors stop firing as much if repeatedly exposed
Taste
Taste sensitivity
**
some people increased liking with increased sweetness, others prefer intermediate levels (Callaghan and Weingarten, 1992).
Taste buds
- how long do they last?
- what happens to food molecules
- how many tastes per cell?
- Only last about 10 days
- Food molecules dissolve in the mouth and bind to receptors.
- One cell – one taste.
- Tastes buds all capable of receiving different tastes (several cells).
Taste: what is involved in neural relay
• Cranial nerve fibres relay this information to the brain.
– Preference for one taste by may respond to others.
• To thalamus – gustatory cortex (anterior insula and frontal operculum).
• Or straight to amygdala- emotion!
How does cortical processing work?
• Cortical cells can respond to all flavours.
• Scott and Plata-Salaman (1999)
– Cortical responses to taste.
– Single cell recordings – tuning preference.
– 1= responds to all tastes, 0=only responds to one taste.
– Average = 0.7
Most cortical cells respond to a variety of tastes but have a preference for one.
Taste adaptation
- what happens
- what happens to water taste after having salt solution on tongue
- *
- can adapt to specific tastes, eg rate tastes as less sour over time
-salt solution on tongue for a while makes pure water taste sweet
What is flavour?
What percentage of taste comes from how we think it smells?
Between 75-95%
What is retronasal olfaction
=smells coming from the mouth
What is orthonasal olfaction
=via the nose
Murphy et al (1977)
**
Stevenson et al (2004)
Caramel odorants can enhance sweetness but also diminish sour tastes.
Oral referral
Olfactory and gustatory stimuli are congruent – get flavour experience
Smell may be “referred” to the mouth.
Taste and Fizz
**
Taste and music
- music influencing choice of wine purchase
- enjoyment of sugar can be enhanced by loud music
- oysters eaten while listening to the ‘sound of the sea’ taste significantly more pleasant than oysters eaten while listening to farm yard nosied
Understanding multi sensory integration
**
Taste primaries
= a theory of taste coding based on the idea that perceived taste can be broken down into basic qualities, each uniquely associated with activity in a specific neural pathway
Umami
A Japanese word meaning ‘good taste’, recent evidence indicates that it is a fifth basic taste quality
Olfactory receptor neuron
A specialised neutron that produces electrical responses to door molecules
Olfactory epithelium
A patch of muscoous membrane in the roof of the nasal cavity containing olfactory receptor neurons, in humans contains 6 million receptor neurons
Free nerve ending
A brand of a sensory nerve cell that has no specialised receptor process, but is embedded directly in tissue
Mitral cell
A neuron in the olfactory bulb that receives signals from olfactory receptor neurons and relays them to the brain, 50,000 mitral cells in the human olfactory bulb
Olfactory bulb
A mass of neural tissue protruding from the brain behind the nose, which conveys neural signals from the olfactory epithelium to the brain
Olfactory glomerulus
A dense, spherical accumulation of dendrites and synapses, where approx 200 olfactory receptors make contact with a single mitral cell
Primary olfactory cortex
The cortical destination of mitral cell fibres, thought to mediate perception of smell
Amygdala
A necleus lying deep in the brain, forming part of the limbic system, involved in emotional, sexual and automatic responses
Anosmia
Lack of sensitivity to door
Taste receptor
A chemoreceptor cell found on taste buds in the mouth, tongue and throat, there are 50-150 recpetors on each bud
Taste bud
A cluster of cells embedded in the skin of the tongue and mouth, housing taste receptors. The human tongue contains approx 5000 taste buds
