Vision Flashcards
What is the signal in vision?
Electromagnetic waves: photons
Packets of electromagnetic energy (quanta)
What is the range of frequencies the eyes can see?
Light particles fall within certain range of frequencies
400-700 nm: range that human visual system response to
frequency = ?
amplitude = ?
Frequency (related to wavelength) of light waves: tells something about the color (hue)
Amplitude of light waves: tells how bright something appears
How is the signal collected for vision? (dilation, constriction, refraction/accommodation)
Amount of light entering the eye is controlled by the pupil.
Wider dilation (controlled by sympathetic ns) means more light which = means more information Constriction (controlled by the parasympathetic ns) to bring the amount of light coming in back down after a stressful event Refraction (bending of light rays) is done by cornea and lens to form an image on the retina (is upside down) Accommodation: ciliary muscles in the eye adjust the focus by changing the shape of lens. Flattened lens for a distant object bc the rays of light are more parallel and dont need as much refraction. Rounded lens for closer object bc light rays diverge and need more refraction
dilation is controlled by?
what does wider dilation mean for the animal?
Dilation is controlled by sympathetic ns
Wider dilation means more light means more information
constriction is controlled by
parasympathetic NS
refraction
bending of light rays
Done by cornea and lens to form an image on the retina (is upside down)
Accommodation
ciliary muscles in the eye adjust the focus by changing the shape of lens
general principles of vision
- Image is upside down
- is in a right/left reverse on the retina
- doesn’t have a one-to-one representation of senses in cortex, so there is a distortion
Example: fovea has 35x more cortical representation than peripheral part of retina; foveal input takes up ~25% of primary visual cortex
retina: which are the photoreceptor cells
rods and cones
what are the differences between rods vs cones? where are they located?
Rods: Highly sensitive to lower levels of light → associated to night vision
Cones: Sensitive to higher levels of light & capable of color vision → mediate daytime vision
Both located at back of retina
Cones located in the middle of the retina, rods located in the periphery (around)
what causes the blind spot in the retina? why do we not see a blind spot in our vision
Optic nerve interrupts the retina → makes a blind spot
Compensation from the cells and other signals to fill in the blind spot
The other eye also maps another part of the visual field to compensate
Range fractionation
- some receptors have high sensitivity (rods) and others low sensitivity (cones); but each receptor has a range of adaptation
each receptor being able to encode varying levels of stimulus
Bipolar cells
receive input from photoreceptors and synapse onto/pass to ganglion cells
Ganglion cells
cells whose axons form the optic nerve
Horizontal cells
makes contact btw photoreceptors and bipolar cells.
Important in lateral inhibition
- Horizontal cells are inhibitory interneurons that release GABA upon depolarization.
- are depolarized by the release of glutamate from photoreceptors, which happens in the dark.
modulate the output of photoreceptors and play many roles in early visual processing contributing to contrast enhancement, color opponency, and the generation of centre–surround receptive fields in cone photoreceptors (cones) and BCs.
Amacrine cells contact bipolar and ganglion cells.
- major carriers of rod signals to the ganglion cells in the retina
- play a role in speeding up the slow potential rod messages for presentation to ganglion cells
make contact with bipolar cells and ganglion cells. They assist in intraocular visual processing. Amacrine cells in particular are important for lateral inhibition.
visual acuity
sharpness of vision
Influenced by density of receptors and mapping to ganglion cells
Greatest at fovea (High concentration of cones)
- every cone is communicating with a ganglion cell
Falls off towards the periphery of the visual field
what kind of potentials do all except ganglion cells produce?
All cell types except ganglion cells generate only graded local potentials
ganglion cells generate action potentials
photoreceptors
Transduce (convert) light into chemical reactions
Disks capture photons
Modulate the transmitter release at the base of the rod
In dark, photoreceptors are really active
Light inhibits activity of photoreceptors