gustatory and olfactory systems (chemical)

Question 1

function of chemical senses

Answer 1

identify food
avoid noxious substances
find a mate and mark territories - with pheromones (debate over whether humans have or use pheromones)

Question 2

gustatory - 5 tastes - salty

Answer 2

relates to vital electrolytes
preference for high levels
needed for physiological processes

Question 3

gustatory - 5 tastes - sour

Answer 3

acidity - high H+ content
preference for avoiding
needed to avoid rotting food

Question 4

gustatory - 5 tastes - sweet

Answer 4

relates to sugars
preference for high levels
needed for energy, growth

Question 5

gustatory - 5 tastes - bitter

Answer 5

relates to diverse chemical structures
preference for avoiding
needed for avoiding toxic or poisonous substances

Question 6

gustatory - 5 tastes - umami

Answer 6

relates to amino acids e.g. glutamate
preference for high levels
needed for protein synthesis

Question 7

evolutionary development with salty and sweet

Answer 7

now have very high access to these - eat too much of it as it used to be more scarce
breast milk is high in sugar as it is what new-borns first crave - makes them want to drink it to get necessary nutrients

Question 8

gustatory system physiology

Answer 8

lingual papillae contain tastebuds
tastebud = group of taste cells

Question 9

gustatory - taste organs

Answer 9

tongue, cheeks, soft palate, pharynx, epiglottis
centre of tongue = texture rather than taste

Question 10

gustatory - the tongue

Answer 10

circumvallate = large evaginations in taste buds
foliate = small version of circumvallate
fungiform = sticks out from tongue with tastebuds on
2-5000 tastebuds on tongue - with ~100 chemoreceptive taste cells per taste bud
taste pore = allows sensory transduction by microvilli

Question 11

gustatory - taste pore receptors (2 types - which tastes are which type)

Answer 11

ion channels:
salty = ENaC channel and another unknown mechanism (removing ENaC channel dampens salty sense but doesn’t remove it fully)
sour = OTOP1 - only discovered in last ~5 years
bitter = T2Rs

G-protein coupled receptor:
sweet = T1R2 and T1R3
umami = T1R1 and T1R3

discovered in knockout mice (removing gene for these specific receptors removes taste sensation)

Question 12

gustatory - specificity of taste cells vs taste buds

Answer 12

taste cell = respond to 1 type of stimuli
taste bud = many taste cells in it respond to range of stimuli

Question 13

gustatory - experiment with bitter receptors in sweet taste cells

Answer 13

putting a bitter receptor into a sweet taste cell increases consumption of bitter tastant - natural preference for sweet foods

Question 14

gustatory afferent cells

Answer 14

separate to taste cells
require neurotransmitter release across synaptic cleft from taste cell to afferent neuron

Question 15

olfactory - physiology

Answer 15

olfactory epithelium (PNS) feeds into olfactory bulb (CNS) then into olfactory cortex (separate to neocortex)
olfactory receptor cells extend into mucous with cilia (increase surface area)
glomeruli (in olfactory bulb) where synapses between OR axons and dendrites are
there is 10cm^2 of olfactory epithelium

Question 16

olfactory - bipolar chemoreceptive neurons (olfactory receptor cells)

Answer 16

odorants dissolve in mucus to reach OR cells
transduction in cilia at end of dendrite
graded potential in dendrite travels down neuron and triggers action potential
primary afferent neuron is axon of olfactory receptor cells

Question 17

olfactory - odorant receptor proteins (OR)

Answer 17

humans have ~350 ORs
olfactory receptor cells only express one OR
one OR can recognise multiple odorants
unique combo of ORs recognise an odorant to distinguish a specific odor

Question 18

olfactory - transduction via Golfs (7 stages)

Answer 18

Golfs = G-protein coupled olfactory receptors

1. molecule binds to receptor
2. confirmational change in Golf
3. alpha subunit of Golf activates adenylyl cyclise
4. ATP converted to cAMP
5. cAMP acts as ligand and binds to cyclic nucleotide gated ion channel (non-selective cation channel)
6. cations enter to cause depolarisation (especially Ca2+ and Na+)
7. Ca2+ acts as ligand and binds to receptor, causing Cl- to move out of cell, furthering depolarisation

Question 19

olfactory - intensity of smells

Answer 19

intense smell = large receptor potential = more action potentials fired
begins in receptor cells as graded receptor potential - summation at cell body
receptor potentials trigger action potentials

Question 20

olfactory - glomeruli

Answer 20

each glomerulus receives input from one type of OR
convergence of second order neurons at glomeruli - many of same type of OR join in a single glomerulus

Question 21

olfactory - link from olfactory bulb to other brain areas

Answer 21

second order neurons carry info from glomeruli to various brain regions:

hippocampus:
olfactory memory = evolutionary, which smell means danger
sex and neuroendocrine = finding a mate, smell of new-born baby for mother

reticular formation:
visceral responses - avoid rotten foods etc

olfactory cortex:
conscious smell

amygdala:
emotional response