Topic 12: The Chemical Senses Flashcards
The partial or complete loss of the sense of smell
Anosmia
Loss of sense of taste
Ageusia
What are the there components of the chemical senses?
Taste
Olfaction
Flavour
When molecules enter the mouth and stimulate receptors on the tongue
Taste
When airborne molecules enter the nose and stimulate receptors in the nasal cavity
Olfaction
Which three properties distinguish the chemical senses from others?
Directly in contact with the external environment
Constantly exposed to the outside world
Regenerate ~ 5-7 weeks for olfaction, and ~ 1-2 weeks for gustation
Describe a positive and negative aspect of the chemical sensory receptors constantly being exposed to the outside world
Pro - easily interact with the chemicals they are supposed to respond to
Con - exposed to harmful materials such as bacteria and dirt
Why are the chemical senses described as “gate-keeper” senses?
Identify things that the body needs for survival, and what can safely be consumed
Detects things that would be bad for the body and that should be rejected
List the five taste qualities
Salty
Sour
Sweet
Bitter
Umami
Why is it adaptive to be able to taste sweetness?
Often associated with compounds that have
nutritive or caloric value, typically carbohydrates
Quickly available energy source
Needed for survival (e.g. glucose and the brain)
Why is it adaptive to taste sourness?
Causes an automatic bodily response that prepares the GI system to get ready to process food (e.g. salivation, stomach acid)
Can indicate fermentation or when something is not ready to be consumed
Why is it adaptive to tase bitterness?
Can trigger automatic rejection responses that help
an organism avoid harmful substances
Why is it adaptive to taste salitiness?
Indicates the presence of sodium - When our bodies are deprived, or we lose a lot sweating, we seek out foods that taste salty to replenish
A homeostatic mechanism in our brains for “thirst” vs.
salt - we need sodium for neurotransmission but don’t want to lose water
Why is it adaptive to taste savoury foods?
Usually indicate protein content - a more long-lasting source of energy for our body
Indicates the presence of glutamate - Main inhibitory neurotransmitter
What are the four categories of papillae on the tongue?
Filiform
Fungiform
Foliate
Circumvallate
Papillae found over the entire surface of the tongue; only ones present in the center
Filiform
Papillae found at the tips and sides of the tongue
Fungiform
Papillae in the form of mounds found at the back of the tongue
Circumvallate
Papillae in the form of folds along the sides and back of the tongue
Foliate
Which type of papillae do not contain taste buds?
Filiform
True or False: Taste qualities are separated into different areas of the tongue
False: all taste qualities come from all parts of the tongue
Why does stimulating the centre of the tongue not produce the perception of taste?
Only filiform papillae are in the center, no taste buds
Where transduction for gustation occurs; converts chemicals from the environment into
electrical activity
Taste cells
Describe the gustatory pathway
Once chemicals contact the
taste cells, electrical activity is produced that is transmitted from the tongue, through the cranial nerves, to the
thalamus, then to the insula/frontal operculum (these two combined make up the primary gustatory cortex - GC)
What seems to explain individual differences in taste?
Genetic differences that affect people’s ability to perceive taste of certain substances
Describe humans’ olfactory detection thresholds
Extremely large range in this
threshold depending on the substance
The source of an odorant/smell
Odour objects
What are the two stages of olfactory processing for perceiving odour objects?
Takes place at the beginning of the olfactory system in the olfactory mucosa and olfactory bulb
Takes place in the olfactory cortex
Explain the role of the olfactory mucosa
Odorant molecules are carried by air into the nose, which brings these
molecules into contact with the mucosa
Once inside they directly contact the olfactory receptor neurons, where olfactory transduction occurs
We have millions of these neurons, but there are only ~400 different types of
olfactory receptors, each being sensitive to only a narrow range of odorants
Pattern of olfactory activation for an odorant that indicates which olfactory receptors will fire
Recognition profile
What occurs when olfactory sensory receptors fire?
The signals are passed to the glomeruli in the olfactory bulb
What are the two main olfactory areas of the brain?
Piriform cortex – the primary
olfactory cortex
Orbitofrontal cortex – the secondary
olfactory cortex
True or false: the olfactory system pathway does not pass through the thalamus
True
The olfactory bulb sends
signals directly to the — and the —
Amygdala and hippocampus (emotion and memory)
Memories about a person’s life that are brought on by smells
Odour-evoked autobiographical memories
A combination of stimulation of the receptors on the tongue and stimulation of receptors on the olfactory mucosa
Flavour
Describe the process of flavour perception
Chemicals in food cause taste when they activate receptors on the tongue
Food releases chemicals
while being broken down in the mouth that reach the olfactory mucosa through the retronasal route
Mapping the two pathways for olfaction and taste, there is overlap in the brain regions
The — cortex seems to be important for our ability to perceive flavour
Orbitofrontal
Connects the oral and nasal cavities
Retronasal route
Give examples of how visual, auditory, and tactile information can influence our perception of flavour
The more coloured a food is, the higher we rate the flavour
If music is playing, we tend to rate foods as being more flavourful
Mouthfeel
