Vision and Eye movements Flashcards
what is the coloured part of the eye?
the lens
what eye structure receives light from the lens?
the retina
what is analogous to the skin?
the retina
where are photoreceptors within the eye located?
in the peripheral retina
what are photoreceptors analogous to?
mechanoreceptors in the skin
what do photoreceptors respond to?
a change in light
what are the types of photoreceptors?
rods and cones
where are rods primarily found?
the peripheral part of the retina
what does it mean that rods are achromatic?
the don’t sense colour
what helps us to see in low levels of light?
rods
are there more rods or cones?
rods! 20:1 ratio
where are cones found in the retina?
centre of the retina (fovea)
what lets us see colour?
cones
what is the region of the retina where axons are leaving?
optic disk
where in the eye are there no photoreceptors?
in the optic disk (blind spot)
is the blind spot the same in both eyes?
no
where does most of our vision come from?
macula
what eye structure is responsible for detailed vision?
fovea
where does all the high acuity vision occur?
in the center of the retina
what are the 2 types of ganglia in the ganglion cell layer of the eye?
parasol ganglion cells
midget ganglion cells
what are characteristics of parasol ganglion cells?
large cell bodies, receptive fields, axons
what are the characteristics of the midget ganglion cells?
small cell bodies, receptive fields, axons
fine visual detail and colour
more numerous
what demographic often has macular degeneration?
people with diabetes
older individuals
what eye structure is impacted with macular degeneration?
macula
what does macular degeneration look like?
central vision affected
what causes diabetic retinopathy?
excess blood sugar damages retinal blood vessels
what does diabetic retinopathy look like?
patty vision loss throughout the visual field
what is cataracts?
blurring of the lens or a clear coating over the eye
what causes glaucoma?
increased intraocular pressure
what eye structure is damaged in glaucoma?
the optic nerve so often peripheral deficits (looks like a spot light)
once information leaves the eye where does it end up in the brain?
primary visual cortex
as visual information comes into the eye, what happens to it?
it gets reversed and flipped upside down
where do 60% of fibres cross?
optic chiasm
what does the optic nerve turn into after the optic chiasm?
optic tract
does the left optic tract contain fibres from the left or right eye?
both! optic tracts have information from both eyes
where is the visual system going through the thalamus?
lateral geniculate bodies
what are the magnocellular layers of the thalamus responsible for?
motion and spatial analysis
(information received from the parasol ganglion cells)
what are the parvocellular layers responsible for?
detailed form and colour
(information from the midget ganglion cells)
what is the conscious visual system?
retina-geniculate pathway
why are the extrageniculate pathways named that?
because they do not go to the thalamus
what are the subconscious visual systems?
extrageniculate pathway
what is the purpose of the pretectum subcortical region?
controls the pupillary light reflex
what is the function of the superior colliculus subcortical region?
controls orienting eye movements?
what is the function of the hypothalamus subcortical region?
regulates circadian rhythms
what artery supplies the occipital lobe?
posterior cerebral artery
where is the primary visual cortex located?
in the occipital lobe
what does the where pathway do?
analyses where something is in space
where does the where pathway go?
up to the parietal lobe
where does the what pathway go?
to the temporal lobe
what happens at the what pathway?
information about form and colour is processed
a lesion in what area of the brain can result in an inability to recognize faces?
right inferior temporal lobe
what is the medical term for the inability to recognize faces?
prosopagnosia
what muscles move the eyes laterally or medially?
lateral and medial rectus
what muscles move our eyes up and down?
superior and inferior rectus
what muscles turn our eyes in the socket?
inferior oblique (extorsion: turn our eyes out)
superior oblique (intorsion: turns the eyes in)
what is the key difference between skeletal muscles and eye muscles?
skeletal muscles are controlled by spinal nerves, eye muscles are controlled by cranial nerves
what are the brainstem gaze centres?
responsible for the automatic control of our extra ocular muscles
what do the brainstem gaze centers do?
direct the movement of the eyes (they coordinate the left and right eyes to move together)
what does conjugate gaze mean?
both eyes move at the same time in the same direction
what is the actual name of the horizontal gaze center?
PPRF
what is the main function of the MLF?
it is yoking the two eyes together
what does it mean that saccadic eye movements are ballistic?
once you start a saccade in a direction, you don’t stop until you’ve rested on the object of interest
what are the purpose of saccadic eye movements?
to bring targets of interest into our central vision
what are saccades directed by?
our gaze enters
what controls our saccades?
superior colliculus
frontal eye fields
what communicates with the PPRF to set off the horizontal eye gaze?
superior colliculus and frontal visual fields
how do we track an object that’s moving?
smooth pursuits
can we do a smooth pursuit without a moving stimulus?
no
smooth pursuits occur via which pathway?
the ‘where’ pathway
what is optokinetic nystagmus a combination of?
saccade and smooth pursuit
what is another term for optokinetic nystagmus?
“train nystagmus”
