Smell & Taste

Question 1

What is the Physiological imp of taste sense?

Answer 1

1. Important for appetite regulation (short term satiety)
2. Feedforward regulation of gut functions e.g. taste signals initiate vagal-mediated gastric, pancreatic & bile secretions
3. Can be protective bec toxic plants have bitter taste.

Question 2

Describe composition of taste buds

Answer 2

50-100 taste cells, supporting cells & basal cells.

Question 3

Describe distribution of taste buds

Answer 3

1. On palate, pharynx & upper esophagus
2. Wall of tongue: upper surface: fungiform, lateral surface (foliate), V-shaped junction between upper & post parts (Circumvallate)

Question 4

Mention sites for each of the basic taste modalities

Answer 4

1. Sweet: tip of the tongue
2. Salt: dorsum of the tongue
3. Sour: edges of the tongue
4. Bitter: back of the tongue

Question 5

Sweet sense is stimulated by…..while umami sense is stimulated by…..

Answer 5

Sugar, amino acids, aldehyde & alcohol
Amino acids mainly glutamate & food additive monosodium glutamate

Question 6

The common final pathway for all tastants is……

Answer 6

Opening of Ca++ channel and release of neurotransmitter

Question 7

Describe mechanism of stimulation for:
1. Salt
2. Sour
3. Sweet
4. Bitter
5. Umami

Answer 7

1. Na+ depolarizes the cells by entering through Na+ channels (leakage channels)
2. H+ depolarizes the cells either by entering through Na channel or blocking K+ channels
3. Act on metabotropic receptor producing cAMP that opens Na+ channels or blocks K+ channels causing depolarization of cell membrane
4. Metabtropic recetors stimulate production of IP3 that inc intracellular Ca
5. Metabtropic (IP3) glutamate receptors

Question 8

What is the physiological importance of smell?

Answer 8

1. Regulate appetite by stimulating reward or aversion. One of the causes if aging anorexia is dec sense of smell
2. Regulates gut functions by conditioned reflexes

Question 9

Describe the mechanism of stimulation of olfactory receptors

Answer 9

Odorant substance dissolves in mucus and binds oforant binding protein forming a complex that binds to receptors on cilia of olfactory sensory cells, that activates adenyl cyclase inc cAMP and open cation channels inc the permeability Na+,K+, Ca++. The net effect is inward Ca++ current that open Cl- channels causing depolarization as Cl- intracellular levels are high in olfactory epithelium. This channels are opened directly by Ca++ or by binding to calmodulin intracellularly. If generator potential reach threshold, action potential takes place in sensory nerve.

Question 10

Describe mechanism of olfactory adaptation

Answer 10

Ca++ will be extruded by Na+/Ca++ exchanger, so restore ion balance, so no more depolarization and no more smell sensation.