The Chemical Senses

Question 1

gustatory system

Answer 1

taste

Question 2

olfactory system

Answer 2

smell

Question 3

functions

Answer 3

identify food sources
avoid noxious substances
find a mate/mark territory

Question 4

chemical senses processing

Answer 4

parallel processing - work together

merge in CNS

Question 5

5 basic tastes

Answer 5

salty
sweet
sour
bitter
umami

Question 6

salty

Answer 6

vital electrolytes
high salt content
required for many physiological processes

Question 7

sour

Answer 7

acidity - H content
aoid high content
avoid rotting food and injury to GI tract

Question 8

sweet

Answer 8

sugars - glucose
high sugar content
required for energy, growth

Question 9

bitter

Answer 9

diverse chemical structures e.g. plants
avoid bitter content
avoid toxic substances, poisonous

Question 10

umami

Answer 10

amino acids e.g. glutamate
high amino preference
protein synthesis and neurotransmission

Question 11

differentiate tastes:

Answer 11

texture
smell
temperature etc

Question 12

taste organs

Answer 12

tongue
cheeks
soft palate

Question 13

types of lingual papillae

Answer 13

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

Question 14

taste pore

Answer 14

contains microvilli where transduction happens
pass through taste cell and meet gustatory afferent nerve
synapse
send info to CNS

Question 15

types of receptor

Answer 15

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

Question 16

specificity of taste cells

Answer 16

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

Question 17

gustatory affeerent are different to taste cells

Answer 17

require neurotranmitter to release across cleft

Question 18

olfactory system components

Answer 18

olfactory epithelium
olfactory bulb
olfactory cortex

Question 19

humans vs dogs

Answer 19

olfactory epithelium:
humans = 10cm2
dogs = 170cm2
dogs have 100x more receptors/cm2

Question 20

odorant pathway

Answer 20

diffuses into mucus
olfactory receptor cells detect it (in olfactory epithelium)
move fro periphery to CNS - brain through crib form plate into glomeruli

Question 21

olfactory receptor cells

Answer 21

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

Question 22

odarant receptor proteins

Answer 22

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

Question 23

transduction

Answer 23

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

Question 24

what is different about [ion] in olfactory cells than other cells?

Answer 24

high intracell Cl

usually low as Cl moves in but in olfactory Cl moves out

Question 25

receptor potentials

Answer 25

trigger action potentials
large enough receptor potential = threshold for ap firing reached
intense stimulus = large receptor pot = ap fired

Question 26

glomerulus

Answer 26

each one of olfactory bulb receives input from only one type of olfactory receptor

Question 27

olfactory projections

Answer 27

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