Lecture 25- Smell

Question 1

What is the plate at the top of the noise called?

Answer 1

Cribriform plate

Question 2

What is contained within the cribriform plate?

Answer 2

There are holes and projecting through these holes are olfactory cells.

Question 3

What form do the cells in the cribriform plate take? Which is it that actually projects though the holes?

Answer 3

These cells are bipolar neurons that have cilia which project through the holes in the cribriform plate

Question 4

What happens in general when we inhale with regards to cell firing?

Answer 4

• When we inhale the chemicals diffuse through mucus layer and come in contact with the olfactory receptor cells
• An action potential is then fired and travels up to the olfactory nerves
• The olfactory nerves join together to form the olfactory bulb
• From here info sent to the brain

Question 5

What do the olfactory nerves join to create?

Answer 5

The olfactory bulb

Question 6

What layer exists at the level of the cilia?

Answer 6

The mucus layer

Question 7

At the receptor level what is causing depolarization?

Answer 7

• Receptors are g-protein coupled receptors which causes an increase in adenylyl cyclase and a conversion of ATP to cyclic AMP
• This results in an opening of calcium and sodium channels= depolarization.
• Chloride exits cell giving further depolarization
• This wave of depolarization reaches the axon hillock. If threshold met then Action potential fires to the olfactory bulb.

Question 8

How many different receptor types and smells can we detect?

Answer 8

• 1000 different receptor types

- Can detect around 10,000 – 50,000 different smells

Question 9

What percentage of smells are perceived as pleasant?

Answer 9

• 20% of these smell are perceived as “pleasant”

- What is perceived as pleasant differs between individuals according to a number of different variables/ adaptations

Question 10

Is the perception of any given smell based on one receptor?

Answer 10

No, its based on a combination

Question 11

Are olfactory axons myelinated or unmyelinated and what do they form?

Answer 11

• Unmyelinated

- Form the first cranial nerve

Question 12

Where do olfactory nerves synapse and what is this the underside of?

Answer 12

• Olfactory bulbs

- Underside of frontal lobes

Question 13

Where in the brain do olfactory bulb axons pass to? What system is this associated with?

Answer 13

• Olfactory bulb axons pass to olfactory cortex
• This is in the limbic system- associated with emotional, food getting & avoiding, & sexual behaviour (primitive part of brain)

Question 14

In the mapping of cortex what two areas are closely associated (to do with senses)?

Answer 14

• Areas for taste and smell (mouth + noise) are together

- These areas are linked

Question 15

Flavor is perceived in the brain as the sum of…

Answer 15

• Input from taste cells
• Input from odour detectors
• Product temperature
• Product texture
• Spiciness (pain!)

Question 16

What is anosmia? What is often the cause?

Answer 16

-Partial or complete loss of smell
-Frequently caused by a swelling or blockage in
the nose
– Irritations to the nose’s mucus membrane
– Blockage of the nasal passage
– Brain or nerve damage

Question 17

Are anosmia and COVID closely related?

Answer 17

• Yes, it’s one of the first reported symptoms of COVID-19
• Believed to affect almost 50% of COVID patients
• COVID-19 invades the supporting cells around the olfactory receptor cells (causing inflammation but not permanent damage)