Unit 9- The Eye Flashcards
What is the structure of the retinae
- retina is made of light sensitive photoreceptors
- rods and cones form synapses with bipolar cells
- bipolar cells form synapses with ganglion cells
What is retinal convergence?
When multiple rod cells connect to a single bipolar cell
What colour are neurones?
Transparent
What happens to rhodopsin when it absorbs light?
- cisretinal absorbs a photon and becomes transretinal
- rhodopsin with trans retinal is unstable so dissociates into free retinal and opsin
This is bleaching
How is rhodopsin resynthesised after being bleached?
Trans retinal is converted back to cis retinal using ATP
And then recombined with opsin
This process is slow
Why are you initially blind when walking from sunlight into a dark room
The reverse reaction of bleaching requires ATP and lots of enzymes so is a slow process
Describe the changes in the rod cell that are caused by light
Light converts retinal into the trans isomer which breaks away from opsin
Opsin causes the Na+ channels to block so the cell becomes hyperpolarised
This prevents inhibitory neurotransmitters release allowing bipolar cell to stimulate the sensory nerve fibre to produce an action potential
Describe briefly what occurs in the rod cell in the dark
- cis retinal in rhodopsin
- Na+ channels are open
- membrane is depolarised
- inhibitory neurotransmitter is released (glutamate)
- bipolar cell becomes hyperpolarised
- less likely for an action potential to be generated
What type of synapse is there connecting the rod cell and bipolar cell?
Inhibitory synapse
What are the 2 types of pigment in the eye cells
- rhodopsin (rods and is more sensitive)
- iodopsin (cones and needs more photons to be bleached)
Why are cone cells more sensitive?
- higher concentration of rhodopsin
- retinal convergence
- 1 photon per come is enough to reach the threshold
Where are the cones and rods located specifically?
Rods- throughout the retina but used for peripheral vision
Cones- in the fovea
How does acuity (resolution) compare between rods and cones.
Rods- poor acuity due to less densely packed and retinal convergence
Cones have high acuity for opposite reasons
What causes colour blindness?
The gene that codes for opsin proteins that detect red and blue light is found on X chromosome so men if the gene is faulty in men then they have no back up copy
