25-26 - Vision Flashcards
The main refractive part of the eye is the…
Cornea (not the lens!)
The pupil allows…
Entry of light into the eye
The iris contains…
Circular and radial muscles controlled by the ANS (determind by light level and emotional signals)
The lens allows for accomodation, the…
adjusting of focus over varying distances
The retina is the layer at the back of the eye, which is in fact part of the brain. It contains (5)…
the photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells and nerve fibres.
Field of vision of each eye is…
150°
Accomodation involves the cillary muscles. When relaxed, they pull the ligaments taught, which…
Flattens the lens (for longer range vision)
When the ciliary muscles contract, the ligaments slacken, which…
Rounds the lens (for closer range vision)
The fovea is located at the…
Centre of the macula
The area of highest visual acuity is the…
Fovea (highest density of cones)
Cones are responsible for…
Colour vision in high light (Photopic)
Rods are responsible for…
Black and white vision in low light (Scotopic)
Ganglion cells and bipolar cells are located (in front of / behind) the rods and cones…
In front of
At the back of the retina is the…
Pigment epithelium in which photoreceptors are embeded
Why does the pigment epithelium contain melanin?
The black pigment prevents scattering by absorbing stray light = improved image quality
Cones come in 3 varieties…
Long reds, green mediums and blue shorts
Rods become…
Bleached in high light
Bleaching of rods is why adaptation to dark…
Takes time
Rods contain rhodopsin which is
Opsin + 11 Cis-retinal
In the dark opsin and retinal are…
Bound
High cGMP, Na+ cannels are open, rod is depolarised and there is constant transmitter release 🌚
In the light opsin and retinal are…
Split (bleaching)
Occurs due to hyperpolarisation of rod, decreasing NT release 🌞
The visual system in the brain is divided into 2 streams (dorsal and ventral) these correspond to…
Where and What respectively
Neurones in the visual cortex are more selective, responding to…
Bars and edges, specific positions and orientations, stimulus moving in a specific direction
Which NT is released by photoreceptors…
Glutamate
