Smell and taste Flashcards
chemical senses
are the oldest and most common form of sense
function of chemical sense
identify food sources
avoid noxious substances
find a mate or mark territories
Even bacteria can sense chemical (chemotaxis)
Primitive function
Eg dogs use pheromones to detect a mate
gustatory system and olfactory system differences
have separate transduction mechanisms
information is processed in parallel
information is merged in the CNa
5 basic tastes
salty sour sweer bitter umami
salty
vital electrolytes, ionotropic receptor
sour
acids, H+ inotropic receptors - fatty acids
sweet
innante fondess, high energy foods, metabotropic receptors (g protein coupled)
bitter
instinctively rejected, often poisonous, metabotropic receptor
umami
delicious in japanese
savoury taste of GLUTAMATE (excitatory neurotransmitter, and amino acid for protein, metabotropic receptor (MSG in fast foods)
perception of flavour
mixture of the receptors activates
and receptors for texture and temperature receptor
craving
when deficit in nutrients
where taste smell touch combined
in the cortex
correct concs of sodium and potassium is really important
will crave salty foods if not enough sodium in body
lingual papillae
taste-sensing strutures
lumpy structures of tongue
taste organs
tongue, cheeks, soft palate, pharynx, epiglottis
most sensitive flavours
sour and bitter
4 types of lingual papillae
filliform
foliate
fungiform
circumballate
filliform
spiked, no taste buds, sense texture, most abundant
foliate
ridges, least abundant, gone by 2-3 years
fungiform
mushrooms, mainly at sides and front
circumvallate
pimples, large, contain about half of all taste buds
taste buds contain
taste cells and gustatory afferents
number of taste buds
2000-5000
about 100 taste cells per taste bud
taste pores
allows stimulus detection by micro villi
gustatory afferents carry
information to central nervous system
papillae have
pores where stimulus enters
side of papillae is where taste bud sits
taste cells
become thin at apex, projecting into taste pore, transducer stimuli into electrical signal
basal cells
like stem cells, renew taste cells every 2-3 weeks
bitter, sweet, umami transduction mechanism
similar systems
(just slightly different receptors but all g protein coupled receptors)
metabotropic
no synaptic vesicles
uses ATP
1) Activation of g protein coupled receptor
2) Activate PLCB2
3) And then iP3
4) Ca released from intracellular stores
5) TrpM5 opens and allows sodium and calcium to enter cell\
6) Sodium moving in causes depolarisation in taste cell
7) VGNC (voltage gated sodium channel) opens causing depolarisation further
8) Release of neurotransmitter at base of cell – ATP is acting as the neurotransmitter
9) ATP moves out of channel
sour transduction mechansism
ionotropic
synaptic vesicles
uses 5-HT, GABA, ATP
1) Ion channels at apical tips permeable to hydrogen ions
2) Already depolarising the cell (so the stimuli itself is already starting the process of depolarisation)
3) Opening of VGNC further depolarisation
4) Activating VGCC (calcium channels) allow calcium into cell
5) Activates the release of synaptic vesicles – a variety of neurotransmitters in vesicles : HT, GABA, ATP
taste cells threshold
they have different threshold for different basic tastes- ‘preferences’
e.g. gustatory axons labelled red receive most inputs from taste cells that respond best to sucrose (sweet), but they also receive input from taste cells that respond to other basic tastes
One taste cell can respond to sweet and salty stimuli for example, but will respond best to one of these stimuli, as it will be detected at a lower threshold.
Gustatory afferents from anterior 2/3rds of tongue are carried in
facial nerve, cranial nerve VII.
logistics of specific taste receptors
We cannot have a completely specific labelled line code, otherwise every flavour would need a specific taste receptor – we don’t have enough proteins for that. So we need to combine the responses of many gustatory afferents using population coding.
odorants
detected as low as a few parts per trillion
must dissolve in the music later to reach olfactory cells
can’t detect chemicals in the air
cavity behind the nose that sense smells
the olfactory receptors re
on the cilia that protect mucsus where the adroitness are dissovled
Axons (thin and unmyelinated) will form cranial nerve I (olfactory nerve)
Basal cells help produce new olfactory neurons (newly made in adults in humans)
transduction occurs via specific g-protein coupled receptors
all odorant receptors are g protein coupled
every one uses the same downstream pathway
When G (olf) activated,
Activate somethhing clycalse and then cAMP
Which opens other ion channels (CNG- cyclic neuclotide gated channel)
Sodium and potassium – graded potential in cilia (dendrite part)
ANO2 allows cholride into and out of cell
Further depolarisation of Cl moving out
anosmic
Golf knock out mice are anosmic i.e. they cannot smell.
odorant receprotr protein genes comprise how much of the entire genome
about 3-5 %
Graded receptor potential
Enough of odorant around to enough of a potential
Produces spikes of AP if above threshold
Large enough receptor potential = threshold for action potential firing reached
Intense stimulus = large receptor potential = increased action potential firing rate
glomerulus of olfactorybulb
received input from the olf receptor cells expressing one specific olf receptor
second order neutron carry info from the glomeruli to various regions of the brain
olfactory projections - conscious smell
conscious smell- olfacotry cortex
olfactory memory
hippocampus
emotional responses
amygdala
visceral responses
reticular formation
sex & neuroendocrine
hypothalamus
which sensory cells release ATP via ion channels rather than synaptic vesicles
taste cells responsive to bitter, umami and sweet
ion channel called calcium homeostasis modulator 1 (CALMH1) when they are stimulated.
CALMH1 is a voltage-gated ion channel that opens as the taste cells depolarise in the sequence of downstream events that occur following the activation of G-protein coupled receptors by bitter, sweet or umami stimuli.
which sensory cells use synaptic vesicles
sour and potentially salty stimuli
don’t use g protein coupled receipts
instead depolarise due to activation of ion channels - traditional method of synaptic vesicle fusion to release their neurotransmitter onto the primary afferent heron when they depolarise
