The Student Room Group
Ooh, wow, I was helping my friend to revise rods and cones yesterday for her Biology mock. I don't do Biology myself, but I know they help you see colour and black and white images. Cones control colour and rods control black and white things.. and that's all I know, hehe!
Reply 2
Anything in particular you want help with, like differences between the two etc..
Reply 3
I've just been revising them for my neuro exam so ask away! :smile:

Random fact: when you go straight from a light to a dark room, it can take up to 40minutes for the rods to adapt! (rods are much more sensitive to light than cones, have lower thresholds and have highly convergent pathways - i.e. synapse on less retinal bipolar neurones!) where as if you go from a dark to a light room your cones adapt straight away giving you your normal vision.
timeofyourlife
I've just been revising them for my neuro exam so ask away! :smile:

Random fact: when you go straight from a light to a dark room, it can take up to 40minutes for the rods to adapt! (rods are much more sensitive to light than cones, have lower thresholds and have highly convergent pathways - i.e. synapse on less retinal bipolar neurones!) where as if you go from a dark to a light room your cones adapt straight away giving you your normal vision.

What do you mean by the "less retinal" bit?
And the quickness is due to cis retinal in rhodopsin being able to change into trans isomer form very quickly when it absorbs a photon or something. The reverse reaction is meant to take much longer but despite using an enzyme ?


Oh and what I always get confused by is the hyperpolarisation and action potential induction, because it's kind of the other way round to a normal nerve cell - in that the neurotransmitter is always being secreted when no light is present, but stops when light is detected (?)

I rephrase a question when I'm less tire
Reply 5
endeavour
What do you mean by the "less retinal" bit?
And the quickness is due to cis retinal in rhodopsin being able to change into trans isomer form very quickly when it absorbs a photon or something. The reverse reaction is meant to take much longer but despite using an enzyme ?


Oh and what I always get confused by is the hyperpolarisation and action potential induction, because it's kind of the other way round to a normal nerve cell - in that the neurotransmitter is always being secreted when no light is present, but stops when light is detected (?)

I rephrase a question when I'm less tire

I think he means retinal as in 'of the retina'!

Yes, when cis-retinal has been converted to trans it takes a set period of time to go back to cis; this gives rise to 'bleaching adaptation', which is one form of light adaptation...

And yes: glutamate is the neurotransmitter here and when there's no light it's continually being released by the photoreceptors. Light causes them to hyperpolarise, leading to no glutamate being released; depending on how the photoreceptors synapse with the bipolar cells (or amacrine AII cells in the case of rods), you get different effects in the postsynaptic cell: some depolarise and some hyperpolarise.

I just hit the revision of this today so ask away if you like! - *hopefully* I can still remember it!