Physiology of Smell

Question 1

What is the area of the olfactory system in each side of the nose?

Answer 1

2-3cm squared

Question 2

What is the second messenger in olfactory transduction?

Answer 2

cAMP

Question 3

What stimulus activates olfactory transduction?

Answer 3

Odorant molecules

Question 4

What is hyposmia?

Answer 4

Reduced ability to smell

Question 5

What is anosmia?

Answer 5

Loss of ability to smell

Question 6

How is olfactory information coded?

Answer 6

Through the pattern of stimulation, which the brain learns to interpret

Question 7

What is olfactory transduction mechanism?

Answer 7

1) Odorant molecules are detected by receptors in the epithelium, leading to the activation of cAMP (2nd messenger)
2) This causes cAMP-dependent ligand-gated ion channels to open, leading to an influx of Ca2+ and Na+ (depolarising the olfactory receptor)
3) Action potential gets produced and Ca2+ indirectly opens Cl- channels so the depolarisation is further contributed to (because Cl- leaves the cell).

Question 8

What factors can cause hypo/anosmia?

Answer 8

• Upper respiratory tract infection
• Ageing
• Nasal polyp (tissue growth)
• Head trauma
• High dosage radiation on nasal epithelium

Question 9

How does olfactory transduction take place?

Answer 9

1) Odorant molecule cause activation of cAMP
2) Activation of cAMP leads to cAMP-dependent channels opening which flux Na+ and Ca2+
3) This leads to depolarisation and leads to Cl- channels opening, leading to Cl- exiting the cell and allowing for further depolarisation (AP then produced if sufficient)

Question 10

What chemical property of olfactory receptors makes them unusual?

Answer 10

They have a high concentration of intracellular Cl-