Lecture 11: Gustatory system

Question 1

What are the flavour stimuli?

Answer 1

Salts, acids (H+, CO2, fatty acids),
(Sugars): glucose/fructose, starch,
(Umami): protein (glutamate)

Question 2

What are the 5 flavours we can discriminate and through which receptor systems do they work?

Answer 2

GPCR: sweet, umami, bitter
Ion channels: Salt, acid

Question 3

Which receptors are involved in ‘sweet’ perception, how do they excite and for what do they have affinity?

Answer 3

For sweet, receptors work together:
- TAS1R2 + TAS1R3 and TAS1R3 + TAS1R3
They activate other taste receptors via IP3 signal transduction that cause Ca2+ release, affecting gustatory afferents.
They have affinity for several sugars

Question 4

Which receptors are involved in ‘umami’ perception, how do they excite and for what do they have affinity?

Answer 4

• TAS1R1 + TAS1R3 (also mGLuR1 and 4)
• Activate other receptors vai IP3 transduction that cause Ca2+ release
• Have affinity for L-amino acids (mainly L-glutamate)

Question 5

Which receptors are involved in ‘bitter’ perception, how do they excite and for what do they function?

Answer 5

• TAS2R1 till TAS2R64 (humans have 25), they are expressed in different combinations
• Has others signal transduction pathways (via PKA and IP3) but Ca2+ release is involved.
• Mainly for poison detection

Question 6

How do Acid receptors work?

Answer 6

H+ depolarizes the cell and blocks rectifying K+ channel K(ir)2.1

Question 7

Which system plays a role in the perception of CO2 and acidity?

Answer 7

Somatosensory system

Question 8

How many taste receptor cells do we have and for which flavour are they responsible?

Answer 8

3 types:
- Type 2 is for bitter, umami, sweet, sweet-umami
- Type 3: acid
- Type 1: glia like

Question 9

Where on the tongue do you find fungiform, foliate and circumvallate papilllae? And for which flavour are they most sensitive?

Answer 9

• Fungiform: tip - umami
• Foliate: middel - bitter(/sour)
• Circumvallate: behind - bitter

Question 10

What is the difference between labeled line or across-fibre pattern in gustation?

Answer 10

• Labeled line: one cell, one flavour
• Acroos-fibre pattern: more flavours per cell or cells sensitive to different flavours that innervate the same afferent cell

Question 11

What is the pathway for gustatory transmission?

Answer 11

NTS (brainstem) –> parabrachial nucelus –> ventral posteromedial nucleus thalamus –> primary gustatory cortex in insula