Taste and smell Flashcards
What were the evolutionary reasons for developing taste and smell?
Finding food, finding a mate, avoiding dangerous substances and homeostasis.
What kind of receptors do taste and smell require?
Chemoreceptors
In what 5 places are chemical senses needed?
- Gustation/taste
- Olfaction/Smell
- Within the skin
- Within the GIT to monitor activity e.g.enzymes
- Internal environment e.g. pH, O2
What can affect present food experiences?
Lifetime experience psychologically affects it
Which two main types of substances does taste allow the detection of?
Poisons e.g. bitterness - Avoided for protection but can acquire a taste for bitter products when known that they’re not poisonous.
Food - Flavour is detected through combined taste and smell.
What is neurogastronomy?
The combing of texture, vision and sound with flavour in the brain to create a perception of the flavour. It combines taste and smell.
What 5 submodalities make up taste?
Salt Sour Sweet Bitter Unami/Savoury Balanced together to create an overall taste
Where are taste cells present?
Tongue, palate and pharynx
What is the distribution of taste cells?
Relative but not absolute. There are certain densities of a submodality that will accumulate in specific areas but they are not restricted to these areas.
Where are the taste buds located?
Contained within the raised protrusions known as papillae.
What is a taste bud?
A groups of cells with the same taste receptor. These receptors are highly sensitive.
In what area is sweet mainly detected?
Tip of tongue
In what are is Bitter mainly detected?
Posterior of tongue
In what are is unami mainly detected?
Centre of tongue
Where are salty and sour mainly detected?
Along the lateral sides of the tongue, with salty most posterior.
What 4 structures are formed by papillae and describe their location?
Vollate - Seperates anterior tongue from lingual tonsil
Fungiform - Lateral sides of anterior
Filiform - Centre of anterior tongue
Foliate - Lateral posterior
Why are taste cells not sensory neurons?
Have no axons so cannot fire an AP
How do taste cells signal?
Synapse with a sensory neuron through the release of NT. They convert a stimulus to a signal for the release of NT to the sensory afferent.
How often are the taste cells replaced?
Every 2 weeks by basal cells
What is the overall sequence of events that leads to an AP?
Chemical binds to taste cell —> Transduction —> Receptor potential —>Depolarisation —> VGCC open —> Ca entry —> NT release —> Excites sensory neuron —> AP
What is transduction?
The method of stimulation of the receptor of a taste cell that varies with each submodality.
Why does the receptor potential not fire?
It is a graded change in membrane potential bu there is no axon to transmit the AP
What is the transduction process of salt?
Na entry —> Depolarisation —> NT release
Na passes down it conc gradient through non-gated channels
What is the transduction process of sour?
H —> Enters via TRP —> Depolarisation
—> K channel block —> Depolarisation
+ve ion entering through non-gate TRP causes depolarisation. Enhanced by K channels that are H sensitive, so closure keeps the cell from repolarising.
What is the transduction of sweet?
Stimulus binds to GPCR which results in Ca entry and causes depolarisation.
GPCR is composed of T1R2 and T1R3
What is the transduction of unami?
Stimulus binds to GPCR which results in Ca entry and causes depolarisation.
GPCR is composed of T1R1 and T1R3
What is the transduction of bitter?
Stimulus binds to GPCR which results in Ca entry and causes depolaristation.
GPCR is composed of T2R and T2R.
What families make up the GPCR for signalling?
T1R and T2R
What happens in the central taste pathway once an AP has been stimulated in the sensory afferent?
Gustatory sensory axon —> CN VII, XI, X —> Brainstem —>Thalamus —> Primary gustatory cortex
The primary neuron passes to the gustatory nucleus in the medulla. Secondary neuron to VPM nucleus of thalamus. Tertiary neuron to postcentral gyrus containing the primary gustatory cortex.
Where is the Primary gustatory cortex?
located above the lateral fissure of temporal lobe on the postcentral gyrus.
What does neural coding require?
The comparison of all inputs
What will a central lesion result in and what might the cause be?
Ageusia - loss of sense of taste
Caused by stroke
Where do the neurons also travel to apart from the gustatory cortex, to form secondary pathways?
To the medulla for digestive functions e.g. swallowing and salivation
To the hypothalamus for satiety and palatability
Where are receptors for smell located?
Lie in the olfactory epithelium at the top of the nasal cavity.
How do molecules get to the neurons?
The molecules diffuse into the mucosa to the cilia of the cells
What is the olfactory N formed by?
Olfactory cell neurons
How are the olfactory cell neurons replaced?
Every 4-8 weeks cells migrate from the wall of the lateral ventricle. Replacement decreases with age
What does the ability of an olfactory cell neurons to be replaced show?
That the adult brain has capacity to generate new neurons
Why is CN I easily damaged?
Ethmoid bone is thin
How many receptor molecules are present on one olfactory cell and are they specific?
Each cell has only one type of receptor but the receptor can bind a range of odorants = non-specific
What is population coding?
The coordinated firing of multiple neurons leading to odorant detection
What is acclimatisation?
The adaptation of a receptor to a continuous stimulus that occurs quickly.
Which has greater sensitivity taste or smell?
Smell
What happens to taste when a blocked nose occurs and why?
Food tastes bland as smell combines with taste to make a flavour
What is the use of smell on its own?
Location detection and pheromones.
When does CN I terminate?
CN I ends in the olfactory bulb and the olfactory neurons continue into the olfactory tract.
What is the sequence of events that leads to firing for the detection of smell?
Odorant binds to receptor —> G protein mediated events —> Intracellular cascade —> Na and Ca channels open —> Receptor potential —> AP
AP only fires if potential reaches threshold.
All the receptors have the same transduction mechanism.
What is a glomerulus?
A collection of neurons in the olfactory bulb that detect similar odors, for the synapse of the glomerulus with a secondary neurone. There are many GPCRs for each type of odor.
What is the central pathway of the secondary neuron?
Secondary neuron passes straight to the olfactory cortex, bypassing the thalamus initially.
Describe the course of the neurons in smell.
Olfactory neuron —> Olfactory bulb —> Olfactory cortex
—> Limbic area = assoctiation
or
—> Medial dorsal nucleus of thalamus —> orbitofrontal cortex = Recognition of smell
Which sense has the strongest association with events and emotions?
Smell
What types of drugs will alter taste and smell?
Drugs that change ions e.g. diuretics
Drugs that change saliva needed for digestion
Chemotherapy as it stops replacement of cells. This can also cause a loss of appetite or a change in palatability / what is liked
What naturally occuring event changes taste and smell?
Age - also linked to a reduced appetite
What condition may alter taste and smell?
Epilepsy - It affects the primary olfactory cortex. Usually a specific smell can be sensed prior to a seizure, acting as a warning.
What will cause the loss of smell?
Damage to olfactory bulb
Parkinson’s disease
Clinical depression - can reverse with AD treatment
