OCB02-2025 Taste & smell

Question 1

What are the 2 environments of the nasal cavity?

Answer 1

Orthonasal

Retronasal

Question 2

What does the orthonasal environment help with?

Answer 2

Helps detect environmental cues and possibly help the human decide whether the food is edible

Question 3

What does the retro nasal environment help with?

Answer 3

Helps send olfactory cues once the food is chewed and processed

Question 4

Why is the olfactory epithelium unique?

Answer 4

It may be the only epithelium with neurones sitting on the top, so they are more susceptible to damage

Question 5

How is sensory function achieved in the olfactory epithelium?

Answer 5

Via the olfactory mucosa

Question 6

Where is the olfactory mucosa located?

Answer 6

In the roof of the nasal cavity

Question 7

What produces nasal secretions?

Answer 7

Made by Bowman’s Glands

Question 8

What do the Bowman’s glands secrete?

Answer 8

Mucins
sIgA
Lysozymes
Odorant Binding Proteins

Question 9

What are the function of Odorant binding proteins?

Answer 9

Increase the solubility of hydrophobic odorants by binding them and transporting them to receptors

Question 10

How many olfactory receptors does each neurone express?

Answer 10

Each neurone only expresses one olfactory receptor but it can bind several odorant molecules

Question 11

How is the olfactory transduction pathway switched on?

Answer 11

Odorants bind to the odorant receptor which results in G protein stimulation upon GDP to GTP exchange on the alpha subunit
This activates Adenylyl Cyclase and increases the formation of intracellular cAMP from ATP
cAMP binds to the Na/Ca ion channel allowing an influx of sodium and calcium ions, depolarising the neuron
Influx of calcium sets up an electrochemical gradient and opens chloride ion channels causing an efflux of chloride ions which helps to amplify the signal

Question 12

How is the olfactory transduction pathway switched off?

Answer 12

NCKX4 is an anti porter which exchanges 3 sodium ions in for every calcium out
Calcium is also taken up by mitochondria
Phosphodiestersase also prevents formation of cAMP

Question 13

What are the anterior 2/3rds of the tongue innervated by?

Answer 13

Chorda tympani and lingual nerve

Question 14

What is the posterior 1/3 of the tongue innervated by?

Answer 14

Glossopharyngeal nerve

Question 15

Why is the production of proteins such as lipase from von Ebner glands so important?

Answer 15

Prevents recurring tastes and allows the taste buds to detect different tastes

Question 16

How often do taste buds turn over?

Answer 16

Every 8-20days

Question 17

What are Type 1 cells?

Answer 17

Glial-like cells that wrap around type 2 and 3 cells

They also have synapse clearing properties as they have enzymes to allow for constant turnover of taste

Question 18

What are type 2 cells?

Answer 18

Have receptors for bitter and umami. but no obvious synapse to nerves

Question 19

What are type 3 cells?

Answer 19

They are pre-synaptic

They detect sour and salt with obvious connections to nerves

Question 20

What are type 4 cells?

Answer 20

Basal cells

Question 21

What are Type 5 cells?

Answer 21

Marginal cells