Olfactory System

Question 1

What is the path of Odour Molecules through nose?

Answer 1

OM diffuse into mucus layer, come into contact with olfactory receptor cells in the olfactory epithelium.
Passes into olfactory bulb through cribriform (Thin bone).

Question 2

General facts

Answer 2

Can detect odours at low concs
Human olfactory epithelium = 10cm2
Dogs have 100x more receptors + larger epithelium

Question 3

Olfactory receptor cells

Answer 3

They are bipolar chemoreceptive neurons.

Regularly replaced

Question 4

Transduction

Answer 4

Transduction machinery found within cilia at end of dendrite.
GP form in cilia, form up the dendrite, transferred to cell body. If GP large enough they become AP.

Question 5

Odorant Receptor Proteins (OR)

Answer 5

G-Protein coupled receptors
Humans have roughly 350 OR’s
but 3-5% of genome dedicated to OR’s
Olfactory receptors cells only express 1 OR
1 OR can recognise multiple odorants
The unique combo of OR that recognise an odorant, allows us to distinguish a specific odour.

Question 6

Transduction:

Answer 6

OR’s use the same downstream pathway:

• G-olf (olfactory Gpro attached to OR’s) / activate
• Adenylyl Cyclase Enzymes / catalyses
• cAMP / binds to and opens
• cyclic nucleotide gated channels / allows Na+ and Ca+ in which
• Depolarisation
• Further depolarisation / as Cl- leaves the cell

Question 7

How is Cl- channels different in cilia?

Answer 7

Normally: Open these channels induces hyperpolarisation which means Cl- enter cell as there is low conc IC.

In Cilia: there is a high conc of Cl- inside the cilia, so when channels open Cl- leaves causing further depolarisation

Question 8

How to trigger AP?

Answer 8

large enough receptor potential = threshold for AP firing reached
Intense stimulus = large receptor potential = higher AP firing rate (freq)

Question 9

Convergence

Answer 9

Different olfactory receptor cells converge onto 1 glomerulus.
Each glomerulus of olfactory bulb receives input from only 1 type of olfactory receptor.
All olfactory receptor cells expressing 1 olfactory receptor protein converges onto 1 glomerulus.

Question 10

Olfactory projections

Answer 10

Olfactory cortex - perceive smell
Hippocampus - links different smell to memory
Amygdala - Emotional responses
Hypothalamus - Sex + neuroendocrine functions
Reticular formation - Visceral response