Lecture 15

Question 1

Individual tastes are encoded at each level of circuit (taste receptor cell–> primary gustatory axons–> …..–> cortex)

Answer 1

Labelled lines hypothesis

Question 2

Responses of a large number of broadly-tuned neurons, rather than than a small number of precisely-tuned neurons, at different levels of circuit are used to specify the properties of a particular taste

Answer 2

Population coding (most plausible)

Question 3

Chemical senses (3)

Answer 3

Gustation- taste
Olfaction- smell
Other chemoreceptors- chemically sensitive cells are distributed throughout the body (eg. nerve endings in digestive organs, oxygen and CO2 detection in arteries, sensory endings in muscle that detect lactic acid build up)

Question 4

5 basic tastes

Answer 4

Salty (salts)
Sour (acids)
Sweet (sugars, artificial sweeteners)
Bitter (K+, MG2+, caffeine and quinine)
Umami (savory taste of amino acid glutamate)

Question 5

Advantages of bitter taste

Answer 5

• poisonous substances are often bitter
• causes an aversive response, but can be modified through experience

Question 6

How are unique flavors distinguished?

Answer 6

1) food activates a different combination of taste receptors
2) distinctive smell
3) other sensory modalities contribute (e.g. texture)

Question 7

Areas that have taste sensitivities (4)

Answer 7

Primarily tongue, regions of pharynx, palate, and epiglottis

Question 8

How do chemicals in the mouth contribute to flavor through olfaction

Answer 8

They can enter through the pharynx

Question 9

Papillae; how many types?

Answer 9

Bumps on the tongue that contain taste buds (from one to several hundred)
3 types

Question 10

Papillae:
Mushroom shaped, located on anterior 2/3 of tongue

Answer 10

Fungiform papillae

Question 11

Papillae:
Pimple shaped, located on the posterior 1/3 of the tongue

Answer 11

Vallate papillae

Question 12

Papillae:
Ridge shaped, located on the sides of the tongue

Answer 12

Foliate papillae

Question 13

Just enough exposure to chemical by single papilla required to detect taste

Answer 13

Threshold concentration

Question 14

Each taste bud consists of: (3)

Answer 14

1) multiple taste receptor cells
2) Basal cells
3) Gustatory afferent axons

Question 15

Taste receptor cell anatomy

Answer 15

Apical end has microvilli that project into the taste pore (microvilli house the receptors)
At bottom of taste bud, taste receptor cells form synapses with the gustatory afferent axons

Question 16

Receptor potential:

Answer 16

Shift in the membrane potential (usually depolarization) when a ligand binds to and activates a taste receptor cell

Question 17

Typically, the receptor potential opens voltage-gated ______ channels to allow an influx of ______, which triggers the release of neurotransmitter from taste cell onto gustatory afferent axons

Answer 17

Calcium, Calcium

Question 18

Transduction mechanism and neurotransmitter released varies on….

Answer 18

Type of taste receptor cell

Question 19

The process by which an environmental stimulus causes an electrical response in sensory receptor cells

Answer 19

Transduction

Question 20

Potential transduction mechanisms by tasants (3)

Answer 20

1) Pass directly through ion channels
2) Bind to and block ion channels
3) Bind to G-protein-coupled receptors and activate second messenger to open ion channels

Question 21

Taste stimuli

Answer 21

Tastants

Question 22

High levels of salt can also activate……

Answer 22

Sour and bitter receptors (mechanisms still unknown)

Question 23

Taste receptors for saltiness:
Chemical stimulant

Answer 23

Salts

Question 24

Taste receptors for saltiness:
Transduction mechanism

Answer 24

Flow through ion channel

Question 25

Salt-sensitive taste receptor cells can be blocked by…

Answer 25

Diuretic drug: amiloride

Question 26

Special Na+-selective channel are always open
Channel is usually open, so when the concentration of Na+ in mouth increases, depolarization depends on extracellular Na+ concentration.
Sufficient receptor potential opens Na+ and Ca2+ channels that trigger release of serotonin.

Answer 26

Salt sensitive taste receptor cells

Question 27

Sourness:
Chemical stimulant

Answer 27

Acids (H+ ions)

Question 28

Sourness:
Transduction mechanism

Answer 28

Flow through H+ ion channels and block K+ ion channel

Question 29

Sour taste receptor cells detect….

Answer 29

High acidity (low pH)

Question 30

Protons (H+) are causative agents of acidity and sourness and can affect the cell in two ways:

Answer 30

Bind to and block special K+ channels– leads to depolarization.
Activate and permeate proton channels that allows H+ ions to flow into the cell– leads to depolarization.
Resultant Ca2+ influx leads to release of serotonin

Question 31

Taste receptors for bitterness, sweetness, and umami:
Transduction mechanism

Answer 31

GPCR binding

Question 32

Rely on dimers (two proteins that are attached to one another) of T1R and T2R families of receptor proteins.
Ligand binding activates the GPCR, leading to IP3 production via Phospholipase C (PLC).

IP3 opens the taste cell specific Na+ channel and the release of Ca2+ from internal storage sites.

Answer 32

Taste receptors for bitterness, sweetness, and umami

Question 33

These cells do not have neurotransmitter filled vesicles, so increased Ca2+ opens an ATP-permeable channel which allows ATP to flow out of the cell and activate purinergic receptors on the gustatory afferent axons.

Answer 33

Taste receptors for bitterness, sweetness, and umami

Question 34

GPCRs consist of proteins from the T2R family.

25 different T2R genes allow for the detection of many different poisonous substances.

Answer 34

Taste receptors for bitterness

Question 35

Detect amino acids (e.g. glutamate)
Requires T1R1 + T1R3 receptors

Answer 35

Taste receptors for umami

Question 36

Requires T1R2 + T1R3 receptors
Same second messenger system as bitter taste receptor cells, but activate unique gustatory afferent axons

Answer 36

Taste receptors for sweetness

Question 37

Main central taste pathway:

Answer 37

Taste buds–> gustatory axons/ cranial nerves–> gustatory nucleus

Question 38

Where is the gustatory nucleus located?

Answer 38

Within the solitary nucleus located in medulla

Question 39

Cranial nerves involved in central taste pathway

Answer 39

VII - Facial: innervates anterior 2/3 of tongue
IX – glossopharyngeal: innervates posterior 1/3 of tongue.
X - vagus: innervates regions around the throat

Question 40

Central taste pathways diverge for…. (3)

Answer 40

Conscious taste experiences
Control of feeding behaviors
Palatability of food

Question 41

Gustatory nucleus–>
ventral posterior medial (VPM) nucleus of the thalamus–>
primary gustatory cortex.

Answer 41

Conscious taste experience pathway

Question 42

Stroke or lesion to primary gustatory cortex or VPM nucleus of thalamus leads to….

Answer 42

Ageusia (loss of taste)

Question 43

gustatory nucleus–>
areas of the brainstem, mainly the medulla, which control swallowing, salivation, gagging vomiting, digestion and respiration.

Answer 43

Control of feeding behaviors pathway

Question 44

Gustatory nucleus–> hypothalamus and parts of the limbic system, like the amygdala. These areas are involved in palatability and motivation to eat.

Answer 44

Palatability of food pathway

Question 45

Lesions to hypothalamus and parts of the limbic system (eg. amygdala) lead to…..

Answer 45

changes in food preferences and over/undereating