Lecture 25 - Smell

Question 1

Olfactory cells

Answer 1

We inhale odours that have chemicals in them and they reach the roof of the nasal cavity known as the olfactory epithelium and within this olfactory epithelium we have holes called the cribriform plate and through these holes porjects the olfactory receptor cells which are actually bipolar nerve cells (shown in yellow) and these receptor cells have these 10-14 non-motile cilia that project though these holes and into the layer of mucus, when we inhale a gas/odour the chemicals within this diffuse within the mucus layer and interact with receptors on the cilia which will stimulate out smell transduction pathway, these bipolar cells also have axons that head out of the olfactory epithelium up to the olfactory nerve and they reach a place called the olfactory bulb which is a small part of the brain that sits just below out frontal cortex which is responsible for our sense of smell

Dogs have bigger olfactory build therefore better at smelling

Question 2

Olfactory signal transduction

Answer 2

Odorant chemicals react with GPCR that is on the membrane of these cilia and this interaction activates an envumre called adenyl cyclase which breaks down ATP into cAMP, the increase in cAMP levels causes the opening of cation channels so get an influx of sodium and calcium into the cilia which causes the opening of the chlorine channels and get chlorine leaving the cilia and causing depolarisation and these depolarisation causes a graded receptor proteins which acts like a wave and goes through the olfactory receptor cell until it reaches the axon hillock, if the depolarisation is great enough at the axon hillock it causes firing of action potentials through the axon to the olfactory bulb

Question 3

Smell =

Answer 3

olfaction

Question 4

Smell receptors and olfaction

Answer 4

We have about 1000 different receptor types
Can detect around 10,000 – 50,000 different smells
Relative activation of different receptor types helps with distinguishing different odours
Only about 20% of these smell are perceived as “pleasant”
These perceptions are modified by a number of variables
The combination of activated receptors is interpreted in the brain to give the quality of the odour

Question 5

Olfactory signal transduction pathway to the brain

Answer 5

Olfactory axons (unmyelinated) form the first cranial nerve
Synapse in olfactory bulbs (on underside of frontal lobes)
Olfactory bulb axons pass to olfactory cortex (in limbic system- associated with emotional, food- getting & avoiding, & sexual behaviour) (- all found very close together in the somatosensory cortex)

Question 6

Taste + smell =

Answer 6

flavour

Question 7

Flavour

Answer 7

Taste + Smell = Flavour

Flavour is perceived in the brain as the sum of
Input from taste cells
Input from odour detectors
Product temperature
Product texture (mouths can detect texture)
Spiciness (pain!)

Question 8

Anosmia

Answer 8

Partial or complete loss of smell
Frequently caused by a swelling or blockage in the nose

Irritations to the nose’s mucus membrane
e.g. cold, hay fever

Blockage of the nasal passage
e.g. tumour or disrupted septums

Brain or nerve damage
e.g. strokes

Question 9

Anosmia and COVID19

Answer 9

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
It is not long term damage as it is not affecting the receptor cells

Question 10

Odorant chemicals

Answer 10

diffuse into the mucus around the cilia, do not interact with receptors on the cilia (do not diffuse directly into them)

Question 11

________ taste receptor cells make up a single taste bud

Answer 11

50 - 100