Chemical senses

Question 1

How often do cells undergo neurogenesis for taste and smell?

Answer 1

Taste - 1-2 weeks

Smell - 5-7 weeks

Question 2

What information do sweetness, bitterness, and saltiness give us?

Answer 2

Sweet - nutritive value
Bitter - harmful substances
Salty - sodium

Question 3

Name the structures of the taste system

Answer 3

Tongue - receptor sheet
Papillae - structures that give tongue rough appearance
Taste buds - 10,00 of them, hold taste cells
Taste cells - 50-100 of them per taste bud
Tips - project from cell bodies upward to taste pores
Taste pores - openings in taste buds that accept chemicals
Receptor sites - located on tips, bind to chemicals

Question 4

Name the four types, shape, and locations of papillae

Answer 4

Filliform - cone shaped, entire surface
Fungiform - mushroom shaped, sides and tip
Foliate - folds, back and sides
Circumvallate - mounds in a trench, back

Question 5

Name the taste signal pathways and their starting locations

Answer 5

Chorda tympani - front and sides
Glossopharyngeal nerve - back
Vagus nerve - mouth and throat
Superficial petronasal - soft palate

Question 6

Describe the signal pathway for taste

Answer 6

Nucleaus of the solitary tract in the spinal cord –> thalamus –> frontal lobe (insula, frontal operculum cortex, orbital frontal cortex)

Question 7

Evidence for population coding

Answer 7

Erickson study: measured firing patterns across nerve fibres of chorda tympani; rats trained to avoid ammonium chloride by being shocked when drinking potassium chloride. Both KCl and ammoniumCl showed similar firing patterns, NaCl pattern different; rats chose to drink NaCl

Question 8

Evidence for specificity coding

Answer 8

Mueller et al. study: created mice that possess a human recept via genetic cloning; receptor responds to bitter substance PTC; licking of GM mice decreased substantially compared to normal mice (didn’t decrease at all)
Amorlide study: blocks flow of Na to taste receptors in rats; brain stem neurons sensitive to Na showed reduced activity to Na; no reduced activity for neurons sensitive to both salty and sour

Question 9

Nontaster, taster, supertaster

Answer 9

Nontaster - not sensitive to PTC and PROP, lacking specialized receptor
Taster - more taste buds, have specialized receptor, sensitive to compounds
Supertaster - more sensitive to bitterness than taster

Question 10

Isolated congenital anosmia

Answer 10

No sense of smell - more insecurity, problems eating with others, less of enjoyment out of life

Question 11

Methods for detecting odors

Answer 11

Yes/no procedure: Ps presented with odors and “blank” smells in successive trials; answer yes or no to whether they can detect it; take 50% detection point as absolute threshold; can result in biased responding
Forced choice: Ps forced to make a choice between two smells - one with odorant, one without; indicate which is strongest; take 75% point as difference threshold

Question 12

Recognition threshold

Answer 12

Concentration needed to identify quality of odor; must increase concentration 3X over detection threshold

Question 13

Puzzle of olfactory quality

Answer 13

Difficulty linking perception of odor quality to its molecular structure

Question 14

Structures of olfactory system

Answer 14

Olfactory mucosa, olfactory receptor neurons (ORN), glomerulus, olfactory bulb

Question 15

Method for measuring ORN responses to odors

Answer 15

Calcium imaging method: concentration of Ca increases when ORN responds to odor; apply chemical that makes ORNs fluoresce; ORN activation causes decrease in fluorescence; measure decease to determine strength of response

Question 16

JND for odors

Answer 16

11%

Question 17

Methods for measuring glomeruli responses to odors

Answer 17

Optical imaging method: cortical cells consume oxygen when activated; red light used to determine oxygen content in cells; measure amount of light reflected by cells; darker areas = greater activation; produces chemotopic map of olfactory bulb
2DG technique: 2DG contains glucose, injected into animal; measure activation by amount of radioactivity present

Question 18

Signal pathway from olfactory bulb

Answer 18

Olfactory bulb –> primary olfactory (piriform) cortex in temporal lobe –> secondary olfactory (orbitofrontal) cortex in frontal lobe –> amygdala

Question 19

Sequence for remembering and recognizing smells

Answer 19

Odor –> chemotopic map activated in olfactory bulb –> scattered activation in piriform cortex –> pattern for odor object

Question 20

Evidence for co-activation of neurons leading to odor memory

Answer 20

Experiment by Wilson: expose rats to either peppermint smell or peppermint + banana smell; after repeated exposure, piriform cortex can distinguish between them

Question 21

Retronasal route

Answer 21

Passage connecting oral cavity with olfactory mucosa; taste influenced by olfaction when nostrils clamped shut

Question 22

Oral capture

Answer 22

Mislocation sensations as coming from mouth, rather than nose

Question 23

Orbitofrontal cortex (OFC)

Answer 23

Receives input from taste, smell, somatosensory cortex, inferotemporal cortex in visual “what” pathway; influences flavor perception

Question 24

Bimodal neurons

Answer 24

Neurons in OFC that respond to both taste and smell, taste and vision

Question 25

Evidence for flavor being influenced by cognitive factors

Answer 25

Plassmann experiment: Ps rate wine with more expensive label as better tasting than wine with less expensive label; actual difference in neural OFC response

Question 26

Sensory-specific satiety

Answer 26

Influence of fullness on pleasantness of food odor

Question 27

Proust effect

Answer 27

Ability of taste and olfaction to unlock memories; may involve links between taste, smell, and either or both the amygdala and hippocampus