The Chemical Senses

Question 1

What do chemoreceptors in the arteries of the neck measure?

Answer 1

CO2/O2 levels in our blood

Question 2

What do nerve endings in skin/mucus membranes warn us of?

Answer 2

Chemical irritants

Question 3

What do sensory nerve endings in muscle respond to?

Answer 3

Acidity

Question 4

What are the innate taste preferences?

Answer 4

We enjoy sweet and avoid bitter flavours

Question 5

What does gustation mean?

Answer 5

Taste

Question 6

What are the 5 basic tastes?

Answer 6

Salt, sweet, sour, bitter and umami

Question 7

What (apart from taste) plays an important role in flavour perception?

Answer 7

Touch, texture, smell and temperature

Question 8

What are the organs of taste?

Answer 8

Tongue, palate, epiglottis, pharynx and nasal cavity

Question 9

What does the palate and epiglottis contain that enables them to be an organ of taste?

Answer 9

Taste buds

Question 10

How are the pharynx and nasal cavity involved in taste?

Answer 10

Odours can pass via the pharynx to the nasal cavity and are detected by the olfactory receptors

Question 11

How many taste receptor cells do each taste bud contain?

Answer 11

50-150

Question 12

What are taste pores?

Answer 12

The chemically receptive end of the taste cell

Question 13

What are taste buds surrounded by?

Answer 13

Basal cells (taste cell precursors) and gustatory afferent axons

Question 14

How do taste receptor cells transmit gustatory information?

Answer 14

Form synapses with gustatory afferent axons

Question 15

What are the two mechanisms of taste transduction and which tastes work by what?

Answer 15

Ion channel mechanisms (salt, sour)

GPCR via T1 and T2 taste receptors (bitter, sweet and umami)

Question 16

What is the salt taste mainly derived from?

Answer 16

Sodium

Question 17

How does sodium cause a salty taste?

Answer 17

Ions pass through the Na+ selective channels down the conc gradients
This depolarises the taste cell, activating voltage gated calcium channels
Causes the vesicular release of neurotransmitter, activating gustatory afferents

Question 18

What do high concentrations of salt activate?

Answer 18

Bitter and sour taste cells

Question 19

What are the determinants of acidity and sourness?

Answer 19

Protons

Question 20

How do we taste sourness?

Answer 20

Protons pass through the channels, bind to and block potassium selective channels. This leads to depolarisation of the taste cell, activating voltage gated sodium and calcium channels to open

Question 21

What are bitter substances detected by?

Answer 21

25 T2Rs

Question 22

What are sweet substances detected by?

Answer 22

T1R2 and T1R3 proteins

Question 23

What are umami substances detected by?

Answer 23

T1R1 and T1R3 proteins

Question 24

What is the T2R coupled to?

Answer 24

Gq pathway

Question 25

What does the Gq pathway do?

Answer 25

Stimulates the enzyme phospholipase C, which leads to the production of IP3
IP3 activates a special type of sodium ion channel and releases calcium from intracellular storage sites

Question 26

Why don’t we confuse bitter, umami and sweet tastes?

Answer 26

Taste cells express either bitter, umami or sweet receptors not both

Question 27

What pathway does taste information take to the brain?

Answer 27

Taste cells -> gustatory axons -> gustatory nucleus -> ventral posterior medial nucleus -> gustatory cortex

Question 28

Where is the gustatory nucleus found?

Answer 28

Medulla

Question 29

Where is the ventral posterior medial nucleus found?

Answer 29

Thalamus

Question 30

What three cranial nerves carry gustatory axons to the brain?

Answer 30

VII (facial), IX (glossopharyngeal) and X (vagus)

Question 31

What are pheromones?

Answer 31

Olfactory stimuli used for chemical communication between individuals

Question 32

What are pheromones important for (in animals)?

Answer 32

Reproductive behaviours, marking territory and indicating aggression or submission

Question 33

What is the olfactory epithelium?

Answer 33

Small sheets of cells high up in the nasal cavity

Question 34

What are the three main cell types in the olfactory epithelium?

Answer 34

olfactory receptor cells, supporting cells, basal cells

Question 35

What do the olfactory receptor cells do?

Answer 35

Transduction

Question 36

What do supporting cells do in the olfactory epithelium?

Answer 36

Function to produce mucus, because odorants dissolve in mucus layer before contacting the cilia of olfactory receptor cells

Question 37

What are basal cells?

Answer 37

Immature olfactory receptor cells that are able to differentiate into mature olfactory receptor cells

Question 38

What are the olfactory transduction mechanisms?

Answer 38

Odorant molecules bind to odorant receptor proteins in the cilia, which activates an olfactory specific G protein.
Adenylyl cyclase activate increases cAMP formation, which allows sodium and calcium influx

Question 39

What do odorants generate in the cilia?

Answer 39

Slow receptor potential

Question 40

Which parts of the brain deal with olfaction?

Answer 40

Frontal cortex, hypothalamus and amygdala and hippocampus

Question 41

What part of olfaction does the frontal cortex control?

Answer 41

Conscious perception of smell

Question 42

What part of olfaction do the hypothalamus and amygdala control?

Answer 42

Motivational and emotional

Question 43

What part of olfaction does the hippocampus control?

Answer 43

Odour memory

Question 44

What is population coding?

Answer 44

The responses of a large number of broadly tuned neurones are used to specify the properties of a particular stimulus