The Chemical Senses Flashcards
gustatory system
taste
olfactory system
smell
functions
identify food sources
avoid noxious substances
find a mate/mark territory
chemical senses processing
parallel processing - work together
merge in CNS
5 basic tastes
salty sweet sour bitter umami
salty
vital electrolytes
high salt content
required for many physiological processes
sour
acidity - H content
aoid high content
avoid rotting food and injury to GI tract
sweet
sugars - glucose
high sugar content
required for energy, growth
bitter
diverse chemical structures e.g. plants
avoid bitter content
avoid toxic substances, poisonous
umami
amino acids e.g. glutamate
high amino preference
protein synthesis and neurotransmission
differentiate tastes:
texture
smell
temperature etc
taste organs
tongue
cheeks
soft palate
types of lingual papillae
contain taste buds —–> contain different taste cells
1 - filiform - spiked, no taste buds, sense texture, most abundant
2 - foliate - ridges
3 - funiform - mushroom shaped, maily at sides and front
4 - circumvallate - pimples, large, contains about half of all taste buds
taste pore
contains microvilli where transduction happens
pass through taste cell and meet gustatory afferent nerve
synapse
send info to CNS
types of receptor
ion channels - salty = ENaC and unkown mechanism (when ENaC was knocked out, could still taste salty) - sour = OTOP1 GPCR - bitter = T2Rs - sweet = T1R2 + T1R3 - umami = T1R1 + T1R3
specificity of taste cells
taste cells only respond to one type of stimuli
experiment:
new bitter receptor created and put in either bitter or sweet cells, bitter tastant given
- in bitter cell, taste was not liked
- in sweet cell, taste was preferred
taste buds contain multiple different taste cells
gustatory affeerent are different to taste cells
require neurotranmitter to release across cleft
olfactory system components
olfactory epithelium
olfactory bulb
olfactory cortex
humans vs dogs
olfactory epithelium:
humans = 10cm2
dogs = 170cm2
dogs have 100x more receptors/cm2
odorant pathway
diffuses into mucus
olfactory receptor cells detect it (in olfactory epithelium)
move fro periphery to CNS - brain through crib form plate into glomeruli
olfactory receptor cells
bipolar chemoreceptive neurons
- odorants must dissolve into mucus layer to reach receptor cells
- transduction machinery is found within cilia at end of dendrite
- primary afferent neuron is the axon of olfactory receptor cell
- axons are thin and unmyelinated
- olfactory receptor cells are regularly replaced - explains why covid can lose smell and regain it
odarant receptor proteins
humans - 350
olfactory receptor cells only express one odorant receptor
one odorant receptor can recognise multiple odorants
the unique combination of odorant receptors allows us to distinguish a specific scent
transduction
occurs by Golfs
odorant receptor proteins are GPCRs
every receptors uses same downstream pathway
Golf —–> adenylyl cyclase —–> ATP - cAMP —–> binds to cyclic nucleotide gated ion channels and opens —–> depolarisation ——> Ca gated ion Cl channels ——> further depolarisation
what is different about [ion] in olfactory cells than other cells?
high intracell Cl
usually low as Cl moves in but in olfactory Cl moves out
receptor potentials
trigger action potentials
large enough receptor potential = threshold for ap firing reached
intense stimulus = large receptor pot = ap fired
glomerulus
each one of olfactory bulb receives input from only one type of olfactory receptor
olfactory projections
second order neurons carry info from glomeruli to various regions of the brain: olfactory cortex = concious smell hypothalamus = sex and neuroendocrine hippocampus = olfactory memory amygdala = emotional response reticular formation = visceral responses
