Eyes Flashcards
Photoreceptors in eyes are metabotropic, what does this mean?
The protein that absorbs the photons is separate from the ion channels
What is a good model for phototransduction?
Mud puppy, large cells in its retina
What are rod cells for?
Use in low light levels, broad colour sensitivity
What are cone cells for?
Used for detail in bright light, sensitive to particular colours
Where is the photopigment in photoreceptor cells?
The discs
What does the receptor potential do?
Regulates neurotransmitter release, do not spike
What happens when photons are absorbed by inner membrane of disc?
Na+ channels close, by cGMP releasing. Membrane potential becomes more negative (goes lower than -35mV)
What are photopigments called?
Rhodopsins
What are the chain of enzyme like reactions that cause increase in membrane potential?
Photopigments change, activates transducing in disc membrane, activated a phosphodiesterase, hydrolyse cGMP
I’m photo-transduction, what is the functional reason of the chain of enzyme like events?
Amplification - high sensitivity in low light conditions
What is a disadvantage of high sensitivity in photo transduction?
Low light levels will saturate cells response
How is strength if light stimulus coded?
Amplitude of receptor potential
What happens when background light level changes?
So too does the photoreceptors sensitivity to light - it adapts to ambient lighting conditions
What do equal contrasts in stimulus strength cause?
Equal increments in response
What do bipolar cells do?
Connect photoreceptor cells to ganglion cells
