Chemical Senses Flashcards
Labelled line code model for smell detection?
This idea suggests that smells are detected from a single receptor channel, activating a single neurone in the CNS, which is detected by a single decoder. This is the output
What does the combinational code for smell detection tell us?
A combination of neurones are activated by multiple signal receptors. Multiple detectors detect this stimulus and this accumulation of knowledge helps to decide a smell.
Odour detections is conserved across species, what does this tell us?
It tells us that the way nerves are laid out must be for some purpose hence the layout being conserved between species
How are weaker signals turned into much stronger signals?
This is in ref to a signal being detected from an odour
Sensory neurones can be used for signal amplification - this is done with a g protein as remember these allow for cascades of signals
What is the process of odour detection?
An odourant molecule will bind to an olfactory receptor
This activates a G protein
This then binds to adenylyl cyclase
This enzyme turns ATP into cAMP
This cAMP opens a cation channel bringing in some calcium and sodium into the cell
This calcium then activates a calcium 2+ activated chloride channel, allowing calcium to move out of the cell.
How can odour signals be amplified?
The enzyme adenylyl cyclase activated by G proteins turn many ATP molcules into cAMP if activated continuously / for a longer time than usual.
This can cause cAMP to open cation channels for longer / more time
This leads to an increase in calcium via amplification meaning more calcium activated chloride channels can be opened / opened for longer, meaning more chlorides leave the cells.
This is how you can cause a single odour binding to a receptor (which in theory shouldnt create a big response) to create a detectable signal.
How do insects detect odours?
Note insects dont have g proteins in their odour detection systems
They rely on ion channels
So suggests signal amplification happens DIFFERENTLY in insects
What was found in odour detection experiments on drospholia?
Some olfactory neurones respond to specific odours whilst others respond to a variety of odours.
What are the different types of olfactory neurones receptors ?
Progenitors, precursors, immature and mature cells
These cells detect different odours. Some detect on odour, others detect multiple.
What happens as olfactory sensory neurones mature?
They choose which receptor they want. I.e. progenitors, precursors.
Where do sensory olfactory neurones which have the SAME receptors all converge?
They synapse on a structure called a glomerlus
Where do odour molecules bind when you at the top of the nasal cavity?
They bind to the olfactory epithelium
This is where the dendrites from the sensory olfactory neurones are found
Where do the axons of all the sensory neurones go to?
They go to the olfactory bulb (this is inwards from the epithelial membrane)
How do olfactory neurones ensure all of their neurones synapse to the same location
These neurones faciliculate (bundle their axons) their axons so they reach the same location.
This same location is the OLFACTORY bulb
In humans sensory information from olfactory neurones go to olfactory bulbs
Where does sensory information go to in drosophila?
These go the antenna lobe
What is important to note about olfactory bulbs and the anntenna lobe in drosophila?
These are all bilateral structures
They are also make of little balls (glomeruli)
What is the conserved circuit of neurones in drosophila and human olfactory systems?
You have primary olfactory receptor neurones, which all synapse onto glomeruli (either the olfactory bulb of the antenna lobes.
You then have interneurones and second order neurones.