vaz Flashcards
How does the light enter our eyes?
The light enters through the pupil (an opening in the center of the iris)
The light is focused by lens and cornea
Light is projected onto the retina
What is the structure of the retina?
The retina contains several layers of
- photoreceptors
- neurone cell bodies
- axons and dendrites
Photoreceptors respond to light energy by firing electrical impulses in the nervous system
How do messages pass in the retina?
From receptors at the back of the eye to bipolar cells
From bipolar cells to ganglion cells
Ganglion cells axons join and then travel to the back of the brain in the optic nerve
Amacrine cells pass info between bipolar and ganglion cells
What are the photoreceptors?
120 million rodes
6.5 million cones
Contain photopigments, chemicals that release energy when struck by light
What are rods?
Abundant in the preiphery of the retina
Provide night vision
What are cones?
Abundant in and near the fovea
Provide colour vision by having 3 different wavelength sensitivity functions
What is trichromacy?
Hermann von Helmholtz
All the colours we see can be mixed by adding 3 colours together
What is the opponent theory?
Hering proposed that we perceive colours in terms of opposites
What is the Retinex theory?
Edwin Land
Cortex compares information from different parts of the retina to determine brightness and colour for each area.
The fovea
Density of rods
- higher in the periphery
- high intensity sensitivity outside of the fovea
- better to look at a dim star out of the corner of your eye
Density of cones
- higher at the fovea centralis (the center of the retina, where light falls from points we fixate)
- greater spatial acuity and good colour vision for objects we are looking at directly
Retinal ganglion cells project to the
* Superior Colliculus (SC) and Lateral Geniculate
Nucleus (LGN), and then
* their signals are relayed to the cortex (V1, primary visual cortex, mostly)
- Superior colliculus
- Found in the dorsal midbrain (above the inferior colliculus)
- Sits below the thalamus
- Very important for commanding eye movement
