Principles of Neuroscience Lecture 10, Gustation & Olfaction Flashcards by Eleanor Nicklason

What is flavour?

Flavour is the sensory experience of food and drink

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What is the different between olfaction and taste?

How do they inter-relate?

Olfaction: volatile chemicals entering nose and landing on olfactory receptor cells
Gustation: chemicals taken into mouth and eliciting response in taste cells

There are separate centres in the brain that deal with each.

Flavour sensation is a combination of both taste and smell.

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What factors influence flavour perception?

Taste
Smell
Appearance
Temperature
Texture
Chilli
Fat

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What is the epiglottis?

Flap of cartilage over the trachea, preventing food entering during swallowing

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Outline the different taste regions of the tongue.

Sweet
Salty
Sour
Bitter

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Why are humans adapted to taste these 5 flavour groups and not others?

These flavours are important because the compound are energy rich (sugar), required for bodily functions (salt), indicate food going bad (sour, acid) or toxicity (bitterness)

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Describe the sensory structures in the tongue

The tongue has papillae which are visible to the naked eye, and contain many taste cells.

Taste cells are the sensory cells of the gustatory system.

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How many taste cells does a normal tongue have?

2000-5000

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Can taste cells be replaced?

Yes, they are turned over every two weeks

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Do individual taste cells is a papillae detect the same chemicals, or different ones?

Taste cells within a single taste bud have different sensitivities.

However, the final output from a taste cell is integrated centrally so as to create the regional sensitivities of the tongue.

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Describe the generalised process of gustatory transduction

Chemicals from food enter the taste pore and interact with receptors on the taste cell.

Depolarisation of the taste cell due to transduction

Fusion of vesicles containing neurotransmitters onto the gustatory afferents

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Describe the path from the taste cell to the brain

Taste cell - Gustatory afferent - medulla, Gustatory nucleus in the solitary nucleus tract - Ventral Posterior Medial Nucleus in the thalamus - Primary gustatory cortex - Hypothalamus - Amygdala

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Which region of the thalamus does gustatory information pass through?

The Ventral Posterior Medial Nucleus

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Which area of the medulla do gustatory neurons pass through?

The Gustatory nucleus of the solitary tract

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Describe Salty transduction in taste cells

Na+ is detected by the amiloride- sensitive Na+ channels.

These sodium channels open, and the cell is depolarised.

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Describe sour sensitivity in taste cells

Protons are detected by a H+ channel

The channel opens and protons rush in, depolarising the cell

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By which receptor is sugar is recognised in taste cells

Sugar acts a ligand on the T1R2/T1R3 heterodimer.

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By which receptor is umami recognised in taste cells?

T1R1/T1R3 heterodimer

Describe transduction after the heterodimer receptor of sugar and bitter tastes in the taste cells

Heterodimer activated
Alpha-gustducin activated (G-protein)
Phospholipase C activated, which makes IP3
TRPM3 channel opened by IP3
Cell depolarised by membrane channel as well as Ca2+ from ER
Vesicles release neurotransmitters onto gustatory afferents

By which receptor is bitter recognised in taste cells?

How does the transduction pathway proceed?

T2R receptor.

This is similar to T1R3 and the pathway is the same after the receptor.

What is the generalised transduction pathway in taste cells?

Ligand binds to receptor, causing opening of Na, K and Ca ion channels
The cell is depolarised by sodium, potassium and calcium
Calcium dependent release of neurotransmitters from vesicles.

Which molecule is umami?

Glutamate

What is special about transduction of glutamate signals?

There are metabotropic receptors on the membranes of vesicles that are activated by glutamate

Which neurotransmitter is released by taste cells?

This is controversial. There are five. It could be any one or a combination of them

Acetylcholine
Serotonin
Glutamate
Noradrenaline
GABA

Where do the gustatory afferents synapse?

In the gustatory nucleus of the solitary tract of the Medulla

Are the projections from the medulla bilateral or contralateral?

Neither, Ipsilateral

Where is the primary gustatory cortex?

Frontal and temporal lobes

What are the two regions of the primary gustatory cortex?

Insula | Operculum

Where are the olfactory receptor cells?

Roof of the nasal cavity

What type of cells are the O.R.C.s?

The olfactory receptor cells are neurons However, they are embedded in the nasal epithelial cells

Describe the process of transduction in O.R.C.s

1. A receptor of the basal end of the O.R.C. detects a odourant molecule 2. G-olf (olfactory G-protein) is activated by the coupled receptor 3. Adenyl cyclase is activated by the G-olf 4. Adenyl cyclase converts ATP - cAMP 5. cAMP interacts with ion channels, causing them to open 6. Ca2+ rushes in, depolarising the olfactory receptor cell. 7. Calcium dependent neurotransmitter release from vesicles

How many types of scents can the human nose detect?

2000

What is the pathway from the O.R.C.s to the brain?

``` O.R.C (axon moves through Cribiform plate) Glomerulus in Olfactory bulb, Second order neurons / mitral cells & granule cells Primary Olfactory cortex Thalamus Amygdala ```

Which neurons form the olfactory nerve?

The second order neurons

What is special about the central pathway for olfaction?

Information from the olfactory bulb goes first to the: - Pyriform cortex - Amygdala etc. Then continues on to: - Thalamus - Hypothalamus - Hippocampus - Orbitofrontal PFC

Describe the structure of the glomeruli. Where are they?

The glomeruli are behind the cribiform plate. The are the axon terminals of the O.R.C.s and the dendrite trees of the second order neurons

What is important about the sensitivity in the glomeruli?

Each glomerulus has information about only one type of smell. If a O.R.C.s has receptors for multiple molecules, the axon will branch into two glomeruli.

What are the "tuning interneurons"?

These are the granule cells. These cells interact with mitral cells, ensuring only one odour per 2nd order neuron

Describe the very specific mapping of odours onto the olfactory bulb

O.R.C.s synapsing with a particular glomerulus have the same receptive field. This information is taken by one second order neuron to that specific olfactory bulb region

How do we perceive flavour?

Information from the gustatory and olfactory sensory cells get integrated in the brain

What is the role of Granule cells?

They are tuning interneurons. They ensure that each mitral cells or other second order neuron is sending information about one odourant

What is a mitral cell?

They are the second order neurons | They connect to the olfactory receptor neurons in the glomeruli

What determines the receptive field of olfactory receptor cells?

The odorant receptors that they to have sets up their 'sensitivity profile' --> they are sensitive to different arrays of molecules

Describe how the glomeruli relate to the receptive field

Each glomerulus receives information about only one odourant, they they have the same receptive field