Vision Flashcards
What is the cornea?
Transparent surface that covers the pupil and iris
What is the sclera?
The white bit of the eye
What is the purpose of the lens?
To focus light rays on the retina (mine sucks because I need glasses)
What is the retina?
The internal lining of the rear 2/3 of the eye
What is the purpose of the retina?
To convert light energy into electrical impulses/neural activity
What is the macula?
The central area of the retina, it’s specialized for central vision
What is the fovea?
The center of the macula and retina, where the image is least distorted
What is the optic nerve made out of?
The axons of retinal ganglion cells
Where are the extraocular muscles located that enable the eye to move?
The sclera
What is light?
Electromagnetic energy emitted in the form of waves - different wavelengths appear as different colours
Which wavelengths of light are visible to the human eye?
400 - 700 nm
The flow of visual information within the retina
Photoreceptors to the bipolar cells to the ganglion cells
Two types of photoreceptors and their purpose
Rods: good for dim light (1000x more sensitive to light than cones)
Cones: good for color, transmit most of the visual information in bright light
Which kind of photoreceptors have the highest concentration in the fovea?
Cones! Rods are more common in the peripheral retina
What makes different cones sensitive to different wavelengths of light to enable colour vision?
Variations in photopigments (all rods have the same photopigment)
What are photosensitive retinal ganglion cells (pRGC)?
Sensitive to blue light, essential for circadian rhythm! (blue light is associated with morning)
Which has lower convergence and resulting higher acuity, rods or cones?
Cones!
Which three color frequencies can the cones in the human eye identify?
Blue, red, and green
What is the opponent process theory? How is it explained?
Color perception is controlled by the activity of two opponent systems (blue/yellow or red/green)
We never see certain color combinations, such as redish-green or yellowish-blue
Where is the blind spot located?
In the temporal hemiretina, where the retinal ganglion cells exit the retina (optic nerve)
What’s the difference between NT-gated K+ and Na+ channels?
NT-gated K+ channels: K+ moves out, causes hyperpolarization and is therefore inhibitory
NT-gated Na+ channels: Na+ moves in, causes depolarization and is therefore excitatory
Which types of cells carry information from your eyes to your brain?
Retinal ganglion cells
How are bipolar and ganglion cells arranged to allow light to strike the foveal photoreceptors directly?
They’re displaced laterally
Do we consciously perceive a blind spot?
Nope! Our brain fills in the blanks
How do images show up on the retina?
They’re inverted!
What is the visual field?
The total amount of space that can be viewed by the retina (different for each eye)
Where do the blood vessels in the eye originate from?
The optic disk (where the optic nerve fibres exit the retina and form the optic nerve)
Are there blood vessels in the macula?
Nope!
What is the half of the retina that is closest to the nose called?
The nasal hemiretina
What is the half of the retina that closest to the temples called?
The temporal hemiretina
Where do the axons of the ganglion cells from the nasal hemiretina cross the midline?
At the optic chiasm
Do the axons of the ganglion cells from the temporal hemiretina cross the midline?
Nope!
What happens if the left optic nerve is cut?
Vision in the left eye will be completely lost, which results in an overall loss of left peripheral vision
What happens if the optic chiasm is transected?
Peripheral vision will be lost bilaterally, or in totality in both eyes
What happens if the left optic tract is cut?
Vision of the right hemifield will be completely lost (one-half of vision)
How does the name of the axons of the ganglion cells change as it crosses the optic chiasm?
Before chiasm, it’s the optic nerve.
After crossing the chiasm, it’s the optic tract
What 2 places do the axons of the optic tract project to?
Superior colliculus and the LGN (in the thalamus)
What are the 2 visual pathways?
Retinotectal pathway: subcortical vision
Retinogeniculostriate pathway: cortical vision
What is involved in subcortical vision?
The retina and superior colliculus
What is involved in cortical vision?
The retina, thalamus (LGN), and primary visual cortex
What percentage of ganglion cells in the retina project to the superior colliculus?
About 10%
Where do the most retinal ganglion cells synapse?
On Lateral Geniculate Nucleus (LGN) neurons in the thalamus
Which LGN receives info about the left half of the visual field?
The RIGHT LGN
Where do most neurons in the LGN project their axons to?
The primary visual cortex
What is the first region of cortex to process visual info via the retinogeniculostriate pathway?
The primary visual cortex
Where is the primary visual cortex located?
In the medial part of the occipital lobe, buried within the calcarine fissure
What are 3 synonyms for the primary visual cortex?
Striate cortex, V1, Brodmann’s area 17
How does the flow of visual information in the retina work?
From back to front! Photoreceptors are in the back, ganglion cells are in the front
Follow the flow of cortical vision
Light to photoreceptors, to bipolar cells, to retinal ganglion cells which form the optic nerve, and after crossing the optic chiasm form the optic tract.
Optic tract leads to LGN in thalmus, then goes to primary visual cortex in occipital lobe, then goes to extrastriate cortex in the occipital, temporal, and parietal lobes
What is the “phosphene threshold”?
The minimum TMS intensity that evokes phosphenes
What does a lower phosphene threshold indicate?
A more excitable visual cortex
How is ecstasy use correlated with phosphene threshold?
Negatively! More ecstasy use equals lower phosphene threshold
Where is visual and auditory information integrated?
The superior colliculus
What is the “ventriloquist illusion”?
When speech appears to be coming from the puppet’s mouth rather than the puppeteer’s mouth
Which system is worse at localizing information: the auditory or visual system?
The auditory system is worse!
Why does the “ventriloquist illusion” work?
Due to the sound source being mislocalized towards a synchronous but spatially discrepant visual event
Where is most sensory information relayed through en route to the cortex?
The thalamus
