Taste and Smell Flashcards
(33 cards)
what type of sense are taste and smell?
- chemical senses
how do we taste?
chemicals dissolve in mouth and stimulate taste buds in the oral cavity
how do we smell?
volatile (gaseous) chemicals are inhaled into the nasal passages where olfactory receptors line the membranes
4 basic taste qualities or sensations
salty, sour, sweet and bitter
substances general taste and chemical compisotion
- salty = produced by organic salts (e.g. NaCL)
- sour = taste from acidic substances (e.g. vinegar)
- sweet = produced by carbohydrates and amino acids (e.g. glucose)
- bitter = produced by alkaloids (often poisonous) (e.g. cocaine)
how many taste buds does the average human have?
10,000
how many types of papillae are on the tongue
3 types
what is the lifespan of each taste bud?
10 days
what are the 3 types of afferent nerve fibres?
- Chorda tympani: Front part of the tongue
- Glossopharyngeal: back region of the tongue
- Vagus: Throat, pharynx and larynx
what are the Neural Pathways for taste perception?
- afferent fibres travel to nucleii in the brainstem and then via the thalamus to the primary taste
- some fibres also project to the orbito-frontal cortex. involved in the behavioural significance significance/reward value of food and perhaps the degree of ‘‘pleasantness’ of sensory stimuli in general (e.g. Francis et al., 1999)
how is taste quality encoded?
- most receptor cells respond to some extent to all 4 basic kinds of taste stimuli, although with different sensitivity
- many taste responsive cells in the thalamus also respond to all tastes
so how does the brain differentiate between substances?
cross-fibre theory
- although most neurones in the taste system respond to several taste stimuli, each responds best (is ‘tuned’) to a particular substance (e.g. salt)
- consequently information about taste quality/identity can be coded in the pattern of activity within an ensemble or group of neurones
what do detection thresholds for taste depend on?
substance tested, temperature, mouth region tested, viscosity and presence other substances
when is taste sensitivity greatest (detection thresholds lowest)?
between 22 to 32 degree C regardless if taste quality
are all papillae equally responsive?
no
why does sensitivity to specific substances vary over the tongue surface
- front = ‘sweet’ & ‘bitter’ tasting substances
- back sides = ‘sour’
- front sides = ‘salt’
- soft palate maximally sensitive to bitter tasting substances
what are two substances are intensely bitter tasting synthesised coumpounds?
phenylthiocarbamide (PTC)
6-n-propylthiouracil (PROP)
what are ‘tasters’?
taste bitter to 50% of population
what are ‘nontasters’?
tasteless or undetectable to 25% of population
what are ‘supertasters’?
extremely bitter, causing choking or gagging to 25% of population
Henning (1916) - 6 primary odour sensations
‘fragrant’, ‘putrid’, ‘ethereal’ (fruity), ‘burned’, ‘resinous’ and ‘spicy’
- in reality its difficult to classify odours reliably using 6 categories
general relationship between a substance’s smell and its chemical properties
- chemical stimuli for olfaction are organic, rather than inorganic, volatile substances
- usually composed of complex mixtures of chemical compounds emitted by vegetation, decaying matter and scent-producing glands of animals
- ability to sense these natural odours have survival value
what are the receptors that mediate smell perception?
- molecules enter nasal cavity → air warmed and humidified by baffles
- olfactory receptors (10million humans) located on olfactory epithelium
- Oderants are picked up by specialised odorant binding proteins in mucus and transported to receptor sites on cilia (finger-like projections) at the end of each olfactory cell
how often are olfactory receptors replaced?
every 4 to 8 weeks
