Liana Machado Eye Section Flashcards
what is the pupil
the opening that allows light to enter the eye and reach the retina
what is the iris
a circular muscle that controls the size of the pupil (the coloured part)
what is the cornea
the transparent surface that covers the pupil and iris
what is the sclera
the “white of the eye”, it is continuous with the cornea
what is the lens
this helps focus rays of light on the retina
what is the retina
the internal lining of the rear two thirds of the eye, it converts images into electrical impulses that are sent to the brain
what is the macula
the central area of the retina that is specialised for vision
what is the fovea
this marks the centre of the retina and macula, the visual image received here is the least distorted.
what is the optic nerve
this is made up of axons and retinal ganglion cells, it carries impulses for vision from the retina towards the brain.
what is light to the eyes
light is electromagnetic energy that is emitted in the form of waves and is visible to the eyes.
what wavelengths are visible to the naked human eye
400-799 nm
how does visual information flow within the retina
photoreceptors - bipolar cells - ganglion cells
what does the retina convert
light energy to neural activity
what are the two types of photoreceptors
rods and cones
what are rods
rod-shaped structures that are specialised for low lighting.
what are cones
these are conical-shaped structures that are specialised for higher light levels and colour vision.
which part of the retina has more rods
the peripheral retina
which part of the retina has more cones
there is a higher concentration of cones in the central retina.
what is the process of visual information in the retina
- light enters
- information about the light flows from photoreceptors to bipolar cells to ganglion cells that project axons out of the eye.
- axons of retinal ganglion cells carry information from eye to brain.
why are bipolar and ganglion cells displayed laterally
to allow light to strike the foveal photoreceptors directly.
where is the blind spot
where the axons of the retinal ganglion cells exit the retina, there are no photoreceptors so sensation of light cannot occur.
what does our brain do to counteract the blind spot in our visual field
fill in our perception of these areas.
are images inverted on the retina
yes
the half of the retina that is closest to the nose is called the
nasal hemiretina
the half of the retina that is not close to the nose is called the
temporal hemiretina
at which degrees is the blind spot located in the temporal hemifield
15 degrees eccentrically.
because the optic disk is located in the nasal hemiretina, what affects the temporal hemiretina
the blindspot
the axons of the ganglion cells located in each nasal hemiretina go where
they cross the midline via the optic chiasm
the axons of the ganglion cells located in each temporal hemiretina go where
they dont cross the midline, they stay on their own side.
what happens if the optic chiasm is transected
peripheral vision will be lost bilaterally
what are axons of ganglion cells called before they cross at the optic chiasm
the optic nerve
what are axons of ganglion cells called after they cross the optic chiasm
the optic tract
where do the axons of the optic tract project to
superior colliculus
lateral geniculate nucleus of the thalamus
for subcortical vision, what is located in the retinotectal pathway
the retina and superior colliculus
for cortical vision, what is located in the retinogeniculostriate pathway
retina
thalamus (LGN)
primary visual cortex
what % of ganglion cells in the retina project to the superior colliculus
10%
what is the map in the superior colliculus
retinotopic map
where are the left and right LGN located
in the thalamus
what are the right and left LGN major targets of
the two optic tracts
where do most retinal ganglion cells synapse on to
LGN neurons
is the right LGN receives information, this comes from…
the left half of the visual field
where do most neurons in the LGN project their axons to
the primary visual cortex
what were the results of the ecstasy and V1 excitability study?
- that participants in the ecstasy group has a significantly lower phosphene threshold than participants in the control group. the frequency of ecstasy use correlated negatively with phosphene threshold.
- within the ecstasy group, the phosphene threshold of participants who hallucinated was significantly lower than the phosphene threshold of participants who didn’t hallucinate.
what was the phosphene threshold
the minimum intensity that evokes phosphenes
what occurs if the TMS coil is placed over the primary visual cortex
when places over the occipital lobe, TMS can elicit light sensation (phosphenes) in the absence of visual stimuli
what is the ventriloquist illusion
the concept that speech seems to be coming from the puppets mouth rather than the puppeteers mouth
why does the ventriloquist illusion occur
occurs due to the sound source being mislocalised towards a synchronous by spatially discrepant visual event (in this case, the puppets mouth).
what is the visual cortex
this lies beyond the striate cortex in the extrastriate areas.
what can researchers identify with the use of single cell recording
they can identify the representational characteristics of neurons in different visual areas.
what is the experiment of single cell recording in the MT.
use of monkeys, are MT, looking at the activity of a single neuron being recorded when a white bar is passed through the neurons receptive field.
the found the neuron fired lots when the bar moved downward toward the left.
this meant that neurons in are MT are selective for the direction of motion.