The Eye (I) Flashcards
What does wavelengths of light allow
Detection of colour
What does the cornea do
Refracts light
What is behind the cornea and what is it controlled by
Pupil - allows light in
Controlled by iris muscles (circular and radial)
What area of the eye allows focus onto retina in close or far vision
Lens
How does lens change shape for close or far vision
Ciliary muscles which attach to lens by zonulas
How is the image reflected on the retina
Inverted and reversed
What does lens accommodation mean
Ability for lens to fatten or flatten depending on close or far vision through its ciliary muscles
What is the lens and focal length like in distant vision (helped by the SNS)
Lens is flattened (ciliary muscles are relaxed)
Focal length is long
What happens for close vision in lens accommodation
Lens fattens/widens via ciliary muscle contraction and zonula slackening (via PNS)
Focal length is shorter (via PNS)
Which area is there the blind spot (no photoreceptors)
Optic disc
Fovea is in the retina, which photoreceptors does it have for high acuity / resolution and colour
Cone receptors
What does light pass through first in retina
Blood vessels and nerve fibres
Explain the structure of retina from back of it
Pigment epithelium Rods/cones Bipolar cells Ganglion cells Blood vessels / nerve fibres
Which pigment do pigment epithelium make at retina and why
Melanin to absorb light
Which cells lay horizontally in retina
Horizontal and amacrine cells
Fovea only contain cone cells, why does it have high visual acuity
Light doesn’t have to pass through blood or nerve fibres first, retina pushes back to expose cone cells in fovea
Which type of light are rod cells for (mainly highest in retina)
Scotopic light - low light levels
Why are rods called contrast
Can’t detect colour only black and white in low intensity light eg darkness (Scotopic vision)
Where does rhodopsin pigment in rods bleach / inactivate
High intensity light
What are the 3 types of fovea cone cells
Low medium and high wavelength cells
What is advantage of cone cells
High resolution/ acuity
Colour vision
What is the vision called using cone cells
Photopic vision
Where is photopigment produced in cone and rod cells eg rhodopsin
Membranous discs in the cells (lipid bilayer)
What does dark adaptation mean
When someone goes from light to dark, they become blind for seconds because rhodopsin is still bleached and cone cells are inactivated in dark
This quickly goes back up when rod cells become active again = dark adaptation
What is the colour vision theory of cone cells called
Trichromatic theory
What does the trichromatic theory mean
The 3 diff wavelength sensitive cone cells at each wavelength have a specific pattern of outputs which make up a colour
Why are red LED lights needed in dark
Rod cells are low sensitive at that wavelength
How is light transduced into signals
Photopigments from the membranous discs
How many pigments are in cones
3 diff ones
What makes up rhodopsin
Opsin protein and 11 CIS retinal
When active (in dark ) what happens to opsin and 11 CIs retinal
they are joined together
What happens to rhodopsin if rods exposed to light
Bleached
Opsin moves away from 11 CIs retinal
In the dark, what are there high levels of at rod cells and why does this allow a high enough membrane potential
Cgmp
Cgmp allows opening of na channels so na moves into rod cells whilst K moves out keeping it at -40mv
Which Nt is released from rod cells in dark when na channels still open due to cgmp
Glutamate
What gcpr is activated when rhodopsin bleaches in light
Transducin
What does transducin do to cause hyperpolarisation at rod cells in the light chasing no Nt release
Lowers cgmp so na channels close
K keeps leaving the cell causing -70 hyperpolarisation
This stops nt glutamate release (inactive rods)
