Unit 7 - Taste and Smell Flashcards
system that detects tastants (water and fat soluble molecules)
gustatory
info on quality, quantity and safety of ingested food
where are taste buds found
type of cells
life span
no of taste buds
taste map hypothesis
on tongue, palate, pharynx, epiglottis, upper oesophagus
taste cells are epithelial, but are electrically excitable and synapse with neurons
life span of 20 days
3-10,000
older thinking of “taste map” incorrect - each taste bud can sense a no of substances but have a preferred stimulus
taste pore
area where volatile substances can be taken up by microvilli on the receptor cells
structure of taste bud
fibres respond best to 1 type of taste but still sense others
innervated by various taste buds
5 taste stimuli
what do tastants interact with
bitter, sweet, sour, salty, umami (MSG)
tastants interact with receptors on microvilli
salty messenger system
Na+
sweet messenger system
cAMP
sour messenger system
H+
bitter messenger system
IP3
overview of taste messenger systems
directly mediated taste stimulants
sour and salt
2nd messenger mediated taste stimulants
bitter and sweet
taste pathway
nerves involved
taste buds synapse with primary gustatory fibres
signal convergence
signal carried by:
- CN VII (facial nerve - anterior tongue and palate)
- CN IX (glossopharyngeal nerve - posterior tongue)
- CN X (vagal nerve - epiglottis and oesophagus)
overview of taste pathway
From thalamus -> gustatory cortex (insula) - maps out different tastants - intensity, have we had it before
volatile molecules reach what system
olfactory system to expand taste perception
ageusia
complete loss of taste
hypogeusia
diminished sense of taste
hypergeusia
enhanced gustatory sensitivity
dysgeusia
distorted taste perception or to a persistent taste sensation in the absence of stimulation
phantogeusia
taste phantoms
stimuli different to what they used to be e.g. sweet not perceived as metallic
reported in patients with epilepsy and schizophrenia
olfaction
odorants provide info about
self, other people, animals and environment
identify food, noxious and hazardous substances
role in social interactions, reproduction and defense
path of volatile odorants
dissolve in nasal mucus (produced in Bowman’s glands in cilia of olfactory epithelium) - mucus protects and supplies odorants to the ORN
olfactory epithelium contains olfactory receptor neurons (ORN)
dendrites of which expand to olfactory cilia
ORN
bipolar
short lived - replaced 30-60 days
G-protein linked receptors ⇒ stimulate cAMP and phospholipase C
structure of olfactory epithelium/ORN
ORNs are sensitive to
single or number of odorants
polymodal
olfactory bulbs
higher levels of an odorant stimulates more neurons - can lead to variations of smell
ORN - bundles to form the olfactory nerves
travel to olfactory bulb and synapse (glutamate) with glomeruli
convergence - each glomeruli, 25 mitral/tufted cells which each receive info from 25,000 ORN
glomeruli respond to particular odorants
2 types of olfactory neurons in glomerulus that project to olfactory cortex
2 types of olfactory neurons in glomerulus that project to olfactory cortex
MITRAL
perception/distinction of smells - limbic effects
TUFTED
sharpen sensitivity of glomeruli to specific odors
olfactory pathways
frontal cortex
conscious perception of olfaction
hippocampus
memory aspects
amygdala
emotional aspects
hypothalamus
hunger and thirst responses to smell, and emotional responses
piriform cortex
→ olfactory cortex - different olfactory stimuli can be placed and identified
quantitative abnormalities - olfactory lesions
loss or reduction of sense of smell (anosmia, hyposmia)
rare, increased olfactory acuity (hyperosmia)
qualitative abnormalities - olfactory lesions
distortions or illusions of smell (dysosmia or parosmia)
e.g. smelling something burning when it’s not there
what can olfactory hallucination and delusions be caused by
temporal lobe disorders or psychiatric disorders
olfactory agnosia
higher order loss of olfactory discrimination
