Lecture 2 - smell And Taste Flashcards
What are the traditional senses?
Smell (olfaction) Taste (gustatory, gustaoception) Hearing (audioception) Sight (vision, opthalmoception) Touch (tactioception)
Temperature
Thermoception
Kinesthetic sense
Propioception
Pain
Nociception
Balance
Equilibrioception
Various internal stimuli
Chemoreceptors
What is the cranial nerve for smell?
Olfactory (I)
What is the cranial nerve for sight?
Optic (II)
What is the cranial nerve for hearing?
Vestibulocochlear (VIII)
What is the cranial nerve for Taste?
Glossopharyngeal (VII, IX, X)
What is the cranial nerve for touch?
Trigeminal (V)
Where are the most common kind of receptor properties found?
Terminal ramifications of a sensory axon that belongs to a pseudo-unipolar ganglion cell
Where are the receptors found in the sense organs located?
Sensory cells that transmit a signal to a ganglion cell
What are the perception of odours closely associated with,
Memories
Emotions
Moods
For humans, what important role does sense of smell have?
Interpersonal communication
Humans can sense over how many different odours?
10,000
What is the detection threshold?
As low as parts per million or even billion
For humans what is smell?
Largely an aesthetic sense
How sensitive is smell in scent-tracking in many animals?
~ 10.000.000
What does smell direct animals to?
Food
Potential mates
Away from danger
Where does the olfactory signalling in humans start?
Nasal cavity - olfactory epithelium
Where does the olfactory receptor neutrons send their axons to?
Olfactory bulb
Where does the second order Neuton transmit to?
Higher cortical areas
What is accessory olfactory pathway (AOP) used for?
Pheromone defection
What is pheromone ?
Species specific
Affect animal behaviour
What is MOP defined as?
Main olfactory system (MOS)
What is AOP defined as?
Accessory olfactory system (AOS)
What does the large family of olfactory receptors recognise ?
Numerous ligands
How many olfactory receptors are there?
~1000
What are olfactory receptors?
GPCRs belonging to the odorant receptor gene family
Class “A” GPCR (Opsin or B-adrenergic receptors)
Who was OR discovered by?
R.Axel
L.Buck
What does a single odour activate?
Multiple ORs
Different combination of ORs are needed for odour recognition
How many OR genes in mouse?
1300 (5% of genome)
How many ORs in humans?
500 ORs (2% of genome. 50-95% sequence homologous)
How many ORs in Zebrafish?
100
How many ORS in C.elegans?
1500 (7% of the genome)
What does C.Elegans consist of?
Nematode
Roundworms
How many neutrons and chemoreceptor genes does C.elegans have?
302 neutrons
1500 chemoreceptor genes (7% of the genome)
How many sensory neutrons express most of the receptors?
32
In mammals, how many olfactory nephron expresses one OR gene?
1
What are olfactory receptor neurons?
Bipolar cells within olfactory epithelium
What does ciliated endings contain?
Odorant receptors that detect odours
Where does axons project to?
Glomeruli in the olfactory bulb
Where does mitral/tufted cells send information to?
Higher brain centres
What is the mechanism of odorant receptors?
- Odorants bind to receptors
- Olfactory receptor cells are activated and send electrical signal
- The signals are related in glomeruli
- The signals are transmitted to higher regions of brain
What does the sensory transduction of odour molecules involve?
Cylic AMP second messenger pathway
What does activation of a receptor by odour molecules activate?
GTP binding protein
What does GTP-binding protein activate?
Adenylate cyclase which produces cyclic AMP
What does cAMP activate?
Cationic cyclic nucleotide-gated channel
Chloride channel
What are olfactory cells?
First order neurons
What are mitral cells?
Second order neurons onto which axons of olfactory cells synapse
What is the neurotransmitter between olfactory cells and mitral cells?
Glutamate
Where does the olfactory neurons send axons to?
Olfactory bulb
What is olfactory bulb composed of?
Layers
What is the peripheral layer?
Glomerular later where the axons of the olfactory neurons terminate