3.1 Gustation Olfaction

Question 1

Define flavour

Answer 1

Sensory experience of food and drink

Question 2

What can food/drink in the mouth activate?

Answer 2

Both gustatory and olfactory afferents (via. diffusion of volatile oderants into the nasal cavity)

Question 3

What are the different tastes (including extras)

Answer 3

<ul> <li>Salt, sweet, umami, sour, bitter (Many have subtypes bitter &amp; sweet)</li> <li>Includes fat, heat (e.g., chilli)</li></ul>

Question 4

What areTaste Buds (1)

Answer 4

Taste buds are a collection of taste receptive cells located at the papillae of the tongue (Not all papillae has taste buds). Humans have 2000-5000 taste buds

Question 5

What are taste cells

Answer 5

<ul> <li>Taste cells are modified epithelial cells, which are made from dedicated stem cells</li> <li>Turnover every 2 weeks (So if taste cells are damaged, taste will return in 2 weeks if stem cells are not damaged)</li></ul>

Question 6

Structure (2) of taste cells

Answer 6

<ul> <li>Apical surface <ul> <li>Taste pore for sampling solution [Exposed to saliva (whatever is in saliva can activate things within the tip of taste buds)]</li> </ul> </li> <li>Basal surface <ul> <li>Communicate with gustatory afferents</li> </ul> </li></ul>

Question 7

Selectivity (2) of taste cells

Answer 7

“<ul> <li>There are 3 types of taste cells in a single taste bud: Each has a different sensitivity</li><li>Although 1 taste cell can respond to several stimuli, they have a preferential response to a single taste</li></ul><div><img></img><br></br></div>”

Question 8

Final Output of Gustation

Answer 8

Final output from taste buds is processed centrally to achieve tastant selectivity

Question 9

Sensory Transduction ofSimple Tastes?

Answer 9

Detected through ion channels

Question 10

Sensory Transduction: Salt (1)

Answer 10

<ul> <li><ul><li>Salt detects Na+ ions and Na+ depolarises taste cells via. amiloride sensitive Na+ channels</li> </ul> </li></ul>

Question 11

Sensory Transduction: Sour

Answer 11

<ul> <li>Sour detects H+ (intracellular acidification/pH levels)</li> <li>Organic acids (vs. inorganic acids) are more effective in lowering intercellular pH</li> <li>Increased acidity blocks K+ leak channels (depolarise)</li> <li>Also opens Na+ Channel (depolarise)</li></ul>

Question 12

Sensory Transduction: Complex Tastes

Answer 12

Activate GPCRs, which activate intracellular pathways, ultimately leading to depolarisation of membrane through opening of channels

Question 13

Sensory Transduction: Sweet

Answer 13

<ul> <li>Activate heterodimer G protein T1R2 and T1R3 receptors</li> <li>Receptors are coupled to phospholipase C, which: <ul> <li>Modulate K+ channels</li> <li>Release Ca2+ from intracellular Ca2+ stores</li> <li>Openings TRPM5 channels, which causes Ca2+ influx</li> </ul> </li></ul>

Question 14

Sensory Transduction: Umami

Answer 14

<ul> <li>Activate heterodimer G protein T1R1 and T1R3 receptors <ul> <li>T1R1 and T1R3 responds to glutamate, enhanced by inosine</li> </ul> </li> <li>Receptors are coupled to phospholipase C, which: <ul> <li>Modulate K+ channels</li> <li>Release Ca2+ from intracellular Ca2+ stores</li> <li>Openings TRPM5 channels, which causes Ca2+ influx</li> </ul> </li></ul>

Question 15

Sensory transduction:Bitter (2)

Answer 15

<ul> <li>Activates homodimer T2R receptor</li> <li>Several types:Come in genetically different forms</li></ul>

Question 16

Location of olfactory epithelium

Answer 16

Roof of the nasal cavity

Question 17

Olfactory epithelium is comrpised of:

Answer 17

Has olfactory receptor cells (neurons) which continuously turn over

Question 18

Projections (2) ofOlfactory epithelium

Answer 18

<ul> <li>Cilia of olfactory receptor cells project into mucus (where odorant dissolves)</li><li>Axons of olfactory receptors cells project through the cribriform plate to the olfactory bulb<br></br></li></ul>

Question 19

Sensory Transduction (5): Olfaction

Answer 19

“<div>Common pathway across all odorants:</div> <ol> <li>Each olfactory receptor neuron expresses a specific receptor protein (GPCR) in its cilia</li> <li>Odorant binds to receptor, activating the G-protein (Golf)</li> <li>Activates adenylyl cyclase, which converts ATP to cAMP</li> <li>cAMP opens cation channels, and Na+ and Ca2+ move into the cell, causing depolarisation</li> <li>Ca2+ in the cell causes opening of Cl- channels, and Cl- moves out of the cell, causing further depolarization (like immature neurons)</li></ol><div><img></img><br></br></div>”

Question 20

Olfactory transduction:Receptive Fields (2)

Answer 20

“Specificity is a property of odorant receptor and central processing<div><br></br></div><div>Different olfactory receptor neurons have different response profiles (‘receptive field’) to arrays of odorants (i.e., respond differently)<br></br></div><div><br></br></div><div><img></img><br></br></div>”

Question 21

Olfactory bulb: Structure

Answer 21

“<ul> <li>Second-order olfactory neurons have branching dendritic trees that form glomeruli with the terminals of olfactory receptor neurons</li> <li>Individual glomeruli only encode 1 odorant</li> <li>Receptor cells that synapse on a particular glomerulus all have the same receptive field (express the same odorant receptor)</li></ul><div><img></img><br></br></div>”

Question 22

Granule Cells: Function in Olfaction

Answer 22

<ul> <li>Granule cells act as tuning interneurons</li></ul>

Question 23

Central olfactory pathway (3)

Answer 23

<ul> <li>Second order olfactory neurons project from the olfactory bulb directly to the olfactory cortex (not via the thalamus!)</li> <li>Some project via the olfactory tubercle to the medial dorsal thalamus, then to the orbitofrontal cortex</li><li>Olfactory information is integrated with mood and affect via the amygdala<br></br></li></ul>