The chemical senses

Question 1

What is taste also known as?

Answer 1

Also known as gustation

Question 2

What are the 5 basic tastes?

Answer 2

• Umami
• Sweet
• Bitter
• Sour
• Salt

Question 3

What can contribute to the perception of flavor?

Answer 3

-Texture and appearance can contribute to out perception of flavour

Question 4

What combination provides us flavor?

Answer 4

A combination of taste smell and touch provide us flavor

Question 5

What are the organs of taste?

Answer 5

• Foliate papillae
• Vallate papillae
• Fungiform papillae

Question 6

What are within our papillae and what reside in them?

Answer 6

WIthin the papillae there are ridges and valleys in which out tastebuds reside

Question 7

What are there within each individual taste bud?

Answer 7

Within each individual tastebud there are segments of taste cells and basal cells

Question 8

What do basal cells replace and do?

Answer 8

Basal cells mature and replace dead taste cells and then the basal cells used are replenished

Question 9

What do microvilli have in taste cells?

Answer 9

Microvilli in taste cells have the receptors to detect the different tastes

Question 10

By what mechanism is saltiness and sourness mediated by?

Answer 10

Saltiness and sourness mediated by ion channel mechanisms

Question 11

By what mechanism is bitterness, sweetness and umami mediated by and via what receptors?

Answer 11

Bitterness, sweetness and umami mediated by GPCR mechanism via T1 and T2 taste receptors

Question 12

What is a major component of salt?

Answer 12

Na+

Question 13

Steps involved in the taste transduction of saltiness

Answer 13

• Na+ passes through Na+ selective channels in microvilli down its concentration gradient
• This depolarises the test cell, activating VGCC’s
• This results in vesicular release of neurotransmitter(Serotonin) and gustatory afferent activated

Question 14

What is H+ the determinant of?

Answer 14

H+ is the determinant of acidity and sourness

Question 15

Steps involved in the taste transduction of sourness

Answer 15

• H+ can pass through the same Na+ selective channels in microvilli that mediate saltiness down its concentration gradient
• H+ also blocks selective K+ channels
• Both these actions depolarise the taste cell, activating VGCC’s
• Results in vesicular release of neurotransmitter(serotonin) and gustatory afferents are activated

Question 16

What is bitterness detected by?

Answer 16

Bitterness is detected by T2 taste receptors of which there are over 30 types

Question 17

Steps involved in the taste transduction of bitterness

Answer 17

T1/T2 receptors are Gq coupled

• PLC converts PIP2 to IP3+DAG
• IP3 intracellularly activates a type of Na+ ion channel and releases Ca2+ from the ER
• Both these actions depolarise the taste cells, activating VGCC’s
• Results in vesicular neurotransmitter release and activation of gustatory afferents

Question 18

What is sweetness detected by?

Answer 18

Detected by a dimer receptor formed from T1R2+T1R3

Question 19

Steps involved in the taste transduction of sweetness

Answer 19

Same signal transduction mechanism as bitterness

Question 20

What do taste cells express to ensure we don’t mix up taste?

Answer 20

Taste cells express either bitter, sweet or umami receptors so we don’t mix up the taste

Question 21

What is umami detected by?

Answer 21

Detected by a dimer receptor formed from T1R1+T1R3

Question 22

Steps involved in the taste transduction of Umami

Answer 22

Same signal transduction mechanism as bitterness and sweetness

Question 23

What is the central taste pathway?

Answer 23

Anterior tongue(CNVII), Posterior tongue(CNIX) and Epiglottis(CNX) transmit information to the gustatory nucleus in the medulla. The information is then transmitted to the ventral posterior medial nucleus and the the gustatory cortex

Question 24

What is smell also known as?

Answer 24

Also known as olfaction

Question 25

What are pheromones?

Answer 25

Are chemical signals that are smelt

Question 26

What are the organs of smell?

Answer 26

• Olfactory bulb
• Cribriform plate of ethmoid bone
• Olfactory tract
• Olfactory epithelium

Question 27

What do we smell with?

Answer 27

Smell with olfactory epithelium

Question 28

What is the olfactory epithelium?

Answer 28

Olfactory epithelium are dendrites of olfactory cells

Question 29

What does the olfactory hairs(cilia) have?

Answer 29

The olfactory hairs (cilia) have a water base containing sugars, enzymes, antibodies and odorant binding proteins

Question 30

How do olfactory receptor neurons function?

Answer 30

• Odorant molecules bind to odorant receptor proteins on the cilia
• Odorant receptor is Golf coupled and is activated
• Adenylyl cyclase activation increases cAMP formation
• cAMP activated channels open, allowing Na+ and Ca2+ influx
• Ca2+ activated chloride channels open enabling Cl- efflux
• This leads to depolarisation of the cell

Question 31

How many olfactory receptor proteins are found in the human genome?

Answer 31

350 olfactory receptor proteins found in the human genome

Question 32

What may olfactory receptor cells express?

Answer 32

May express only one receptor protein

Question 33

What does each receptor protein respond to?

Answer 33

Each receptor protein responds to odors to a greater or lesser extent

Question 34

What are smells differentiated due to?

Answer 34

Smells are differentiated due to population coding

Question 35

What are temporal and spatial cues seem important for?

Answer 35

Temporal and spatial cues seem to be important for decoding olfaction

Question 36

What is the central olfactory pathway?

Answer 36

Olfactory receptor cells(CN1) to the olfactory bulb.
From olfactory bulb to the followig:
-Frontal cortex
-Hypothalamus amygdala
-Hippocampus

NB: Doesn’t have to go via thalamus before anywhere else