Retina Flashcards
Sequence of cells from light entering eye to optic nerve
- Light travels to back of eye (neurons transparent)
- Cones / rods
- If through rods, then additionally through rod bipolar cells and amacrine cells
- Cone bipolar cells
- Ganglion cells
- Optic nervee
Difference between rods and cones
Rods are sensitive to light in general and not specific wavelengths, more spread throughout retina
Cones are more sensitive to different wavelengths and are more concentrated on fovea
How do photoreceptors detect light?
Rhodopsin, when exposed to light, will release enzymes that open Na+ channels, leading to hyperpolarisation
Retinal colour blindness
Absence of cone type
10x more likely in males (especially Africans and Asians)
Ishihara plate
Plate used to assess colour blindness
Fovea
Cup-shaped area of retina with highest density of photoreceptors, most cones are concentrated here, contained within macula
Blind spot
Area where optic nerve goes towards brain, this area has no photoreceptors
Age-related macular degeneration
Dry AMD develops underneath retina and causes blurriness, dark spots and distortion.
Can develop into wet variant if blood vessels develop behind retina, damaging photoreceptors and bleeding.
Risk factors: age, smoking, diet, genetics
Treatments: none found
Retinal pigment epithelium
Pigmented layer in retina.
In humans, this absorbs light to prevent scattering, leading to more precise and sharper vision compared to cats, for example, in which it disperses light leading to more sensitive but less sharp vision
Glaucoma
Increase of retinal pressure
- prevents blood flow in retina
- decreased oxygen and nutrients
- permanent damage
- first affects peripheral vision
Eye pressure
Ocular fluid enters through ciliary body and leaves through trabecular meshwork
Difference between action and graded potentials
Action potentials have an all-or-nothing response, once induced, will not vary in intensity according to stimulus strength. Graded potential strength is relative to strength of light exposure
Global prevalence
Global target spotted before local target
Why? Magnocellular layers in LGN have axons that are faster than those in parvocellular layers
Global information is mainly processed in right hemisphere, local information mainly in left hemisphere
