chemical senses

Question 1

where are chemoreceptors located and what do they measure?

Answer 1

in the arteries of the neck, measure co2 and o2 levels in the blood

Question 2

how are we warned of chemical irritants?

Answer 2

nerve endings in skin/mucous membranes

Question 3

how do we detect acidity?

Answer 3

sensory nerve endings in muscle respond to acidity

Question 4

what is gustation?

Answer 4

taste

Question 5

what is smell?

Answer 5

olfaction

Question 6

how do we perceive flavour?

Answer 6

smell, taste and touch

texture and temperature

Question 7

name some organs of taste other than the tongue

Answer 7

• palate
• epiglottis
• pharynx and nasal cavity

Question 8

palate

Answer 8

Roof of mouth separating oral and nasal cavities

Question 9

where are taste buds present?

Answer 9

palate and epiglottis

Question 10

epiglottis

Answer 10

Leaf shaped cartilage covering laryngeal inlet upon swallowing

Question 11

pharynx and nasal cavity

Answer 11

odours can pass via the pharynx to the nasal cavity

-here, they are detected by olfactory receptors

Question 12

what are papillae?

Answer 12

structures on the tongue

Question 13

different papillae shapes?

Answer 13

fungiform = mushroom shaped
foliate = ridged shaped
vallate = pimple shaped

Question 14

cross section of a papillae?

Answer 14

taste buds embedded into them

• chemically sensitive end of a taste bud is a taste pore
• taste cells are within this, connect and synapse with the gustatory afferent axons, which transmit taste information to the brain

Question 15

what is a taste pore?

Answer 15

chemically sensitive end of a taste bud

Question 16

what are taste cells?

Answer 16

they are within the taste pores

they connect and synapse with the gustatory afferent axons, which transmit taste information to the brain

Question 17

what do taste receptor cells express?

Answer 17

express different types of taste receptors

• display different sensitivities to sweet, bitter, sour, salt
• can be measured in AP discharge

Question 18

five different tastes are transduced via?

Answer 18

different mechanisms

Question 19

saltiness and sourness transduced via?

Answer 19

ion channel mechanisms

Question 20

saltiness taste transduction mechanism

Answer 20

• Na+ passes through Na+ selective channels down its conc gradient
• depolarises the taste cell and activates VGCCs
• vesicular release of neurotransmitter
• gustatory afferents activated

Question 21

what is the special Na+ selective channel and its role?

Answer 21

it is amiloride sensitive, and used to detect low concentrations of salt – insensitive to voltage and generally stays open

amiloride – diuretic drug that antagonises this paticular receptor

Question 22

sourness taste transduction mechanism

Answer 22

• H+ passes through Na+ selective channels down its conc gradient
• H+ also binds to and blocks K+ selective channels
• Both these actions depolarise the taste cell, activating VGCCs
• vesicular release of neurotransmitter
• gustatory afferents activated

Question 23

bitterness, sweetness and umami transduced via?

Answer 23

T1 and T2 taste receptors

-T1 family and T2 family

Question 24

what are T1Rs and T2Rs?

Answer 24

They are 2 families of related taste receptor proteins

G-protein coupled receptors, specifically Gq coupled – form dimers

Question 25

bitter substances are detected by which receptors?

Answer 25

2 T2Rs

Question 26

Sweet substances are detected by?

Answer 26

one receptor – T1R2 and T1R3 proteins

Question 27

Umami substances are detected by?

Answer 27

one receptor – T1R1 and T1R3 proteins

Question 28

bitterness transduction mechanism?

Answer 28

- Bitter tastants binds to T2 receptor - Gq coupled - Stimulates phospholipase C which converts PIP2 to IP3 and DAG - IP3 intracellularly activates a special type of Ca+ ion channel, releasing Ca2+ from the ER Taste cell depolarised, release of ATP, gustatory afferents activated

Question 29

sweetness transduction mechanism?

Answer 29

Sweet tastants binds to dimer receptor (T1R2 and T1R3) - Gq coupled same signal transduction mechanism as bitterness

Question 30

Why do we not confuse bitter, sweet and umami tastes if the mechanisms are the same?

Answer 30

because taste cells express either bitter, sweet or umami receptors – not all three bitter, sweet and umami taste cells connect to different gustatory axons

Question 31

umami transduction mechanism?

Answer 31

Umami tastants bind to dimer receptor (T1R1/T1R3) - Gq coupled same signal transduction mechanism as bitterness and sweetness occurs

Question 32

what do umami and sweetness have in common?

Answer 32

both have T1R3 protein - so the other T1R subunit determines specificity to sweetness or umami

Question 33

What is the flow of taste information to the CNS?

Answer 33

anterior tongue/posterior tongue/epiglottis --> gustatory nucleus --> ventral posterior medial nucleus --> gustatory cortex damage at any point within these pathways, it would result in people not being able to taste certain things

Question 34

are taste and smell innate or learnt?

Answer 34

some taste/smell preferences are innate | -however experience can strongly modify our innate preferences

Question 35

what do we smell with?

Answer 35

the olfactory epithelium

Question 36

what is the the olfactory epithelium?

Answer 36

small, thin sheet of cells high up in the nasal cavity -dendrites of olfactory cells that protrude from olfactory bulbs through the holes in our skull (cribiform plate), into the top of THE nasal passage 1. olfactory receptor cells - site of transduction Each of the olfactory cells expresses a type of olfactory receptor protein 2. supporting cells - help produce mucus 3. basal cells - immature olfactory receptor cells – source of new olfactory receptor cells

Question 37

role of the cilia (protrusions from olfactory cells)

Answer 37

cilia are covered in a mucus layer containing sugars, variety of enzymes and odorant binding proteins

Question 38

what do the odorant binding proteins in the mucus layer do?

Answer 38

catch the smell particles and present them to the cilia of the olfactory receptor cells

Question 39

what is it important that the mucus layer contains antibodies?

Answer 39

because certain viruses/bacteria commonly enter our bodies through our nasal passage

Question 40

olfactory transduction mechanism

Answer 40

- Odorant molecules bind to odorant receptor proteins on the cilia, activate Golf - AC activated, cAMP formation increased - cAMP-activated channels open, Na+ and Ca2+ influx - Ca2+ activated chloride channels, Cl- efflux - cell membrane depolarisation

Question 41

after depolarisation what happens to AP's generated?

Answer 41

- odorants generate a slow receptor potential in the cilia - receptor potential propagates along the dendrite and triggers a AP's in olfactory receptor cell soma - propagated along the olfactory nerve axon to the brain

Question 42

where do the olfactory nerve axons go?

Answer 42

into the olfactory bulb | -signals relayed in the glomeruli and transmitted to higher regions of the brain

Question 43

explain convergence that occurs?

Answer 43

olfactory receptor cells expressing the same receptor proteins project to the same glomeruli in the olfactory bulb - convergence

Question 44

which higher regions of the brain are signals transmitted to?

Answer 44

frontal cortex - conscious perception of smell hypothalamus and amygdala - motivational/emotional aspects of smell hippocampus - memory

Question 45

Population coding for gustation and olfaction

Answer 45

axons in the brain responds broadly to smell, so combinations of patterns are used so they can detect which smell it is (different response patterns)