Give a quick summary of how vision works?
1. The amount of light hitting the retina is regulated by the eye 2. Lights falls upon the rods and cones in the retina 3. Energy from waves of photons is changed into signals 4. Brain receives and interprets signals
Describe the order of the cells of the retina involved in signal transmission? (Front of the eye to the back)
- Optic Nerve Cells - Ganglion Axons - Ganglion Cells - Bipolar Cells - Photoreceptors
Describe the direct pathway for signal transmission?
- Photoreceptors - Bipolar Cells - Ganglion Cells - Ganglion Axons - Optic Nerve
Describe how the retina is considered 'back to front' when it comes to signal transmission?
The optic nerve cells and ganglion axons are furthest forward The Photoreceptors are furthest back However, light hits the photoreceptors first then travels forward
What are the two types of photoreceptors?
Function of photoreceptors?
Convert light into neural signs
Describe rods and cones?
Rods are found on the periphery and work best in dark, low level light conditions (Eg: Night) Cones are central and work best in high level light conditions (Eg: Daytime) and colour
Describe the structure of a photoreceptor?
Synaptic Terminal Inner Segment Cell Body Outer Segment
What is in the outer segment of photoreceptors?
There is are membranous disks containing photopigment
Describe the physiology of phototransduction?
Photoreceptors have a depolarized resting membrane potential When light is shone, a cGMP-gated Na+ channel closes This causes hyperpolarization The change in Na+ is the signal that allows the brain to perceive objects in the visual field
What channel is involved in phototransduction? When is it open, when is it closed? What is this current called?
cGMP-gated Na+ channel Closed during light, open during dark This is the dark current
What is the dark current?
This is a cGMP-gated Na+ channel that is open during the dark and closed during the light
What is the photopigment in rods called?
What is retinal? Where is it found?
Retinal is the light-absorbing part of photopigment Opsin (the G-protein coupled receptor) makes a pocket where retinal is found
Rhodopsin = X + Y What does X mean? What does Y mean?
Rhodopsin = Opsin + Retinal Opsin is a G-protein coupled receptor Retinal is the light absorbing part
What confirmation of Retinal is used in phototransduction?
What is retinal derived from?
What happens when 11-cis-retinal absorbs a photon of light?
It becomes all-trans retinal This is the active form
What happens once 11-cis-retinal has been converted into all-trans-retinal?
This causes closure of cGMP Na+ Gate There is reduced Na+ entry This results in hyperpolarization
http://sites.sinauer.com/neuroscience5e/animations11.02.html Watch this animation
What molecule regulates the dark current?
What facilitates visual acuity?
Where is the highest number of cones?
Where is the highest number of rods?
What part of the electromagnetic spectrum can we detect?
Only visible light
What colour do the short wave cones detect?
What colour do the medium wave cones detect?
What colour do the long wave cones detect?
Compare visual acuity between rods and cones?
Rods = Low Visual Acuity Cones = High Visual Acuity
Compare convergence between rods and cones?
High Convergence = Rods Low convergence = Cones