4 - The Visual Pathway Flashcards
10 layers of the retina:
RPE Photoreceptors External Limiting Membrane Outer Nuclear Outer Plexiform Inner Nuclear Inner Plexiform Ganglion Cell Nerve Fiber Layer Inner Limiting Membrane
the visual pathway begins in the photoreceptors, followed by 3 neuron chain:
bipolar - ganglion - neurons in LGN of thalamus
photoreceptors release glutamate to bipolar cells in _
the dark (inhibitory)
OFF bipolar cells are _ receptors
less glutamate (light) = _ cation conductance
cell _
ionotropic
less
hyperpolarizes (does not fire)
ON bipolar cells are _ receptors
less glutamate (light) = _cation conductance
cell _
metabotropic
more
depolarizes (AP fired)
ON and OFF cells are always working to detect changes in light levels
increased light - _ depolarizes
decreased light - _ depolarizes
ON
OFF
ON bipolar cell synapses with _ ganglion cell;
ON ganglion cell _ when signal comes from center as opposed to surround
ON
fires more rapidly
3 ganglion cell types:
midget, parasol, bistratified
Midget ganglion cells make up the majority of the cells that project to the _
origin of the _ pathway
LGN
parvocellular
parasol ganglion cells make up _% of cells that project to LGN
origin of the _ pathway
10
magnocellular
bistratified ganglion cells make up _% of cells that project to LGN
origin of _ pathway
8
koniocellular
midget cells (parvo) detect _ parasol cells (magno) detect _ bistratified (konio) detect _
color (R/G), detail
motion, contrast, shape
blue and yellow
projection of visual fields on each retina are _ and _
inverted and perverted
at LGN, visual field information is _
lateralized
some fibers _ LGN
bypass
bypass LGN:
pupillary fibers -> _
pretectal nucleus
bypass LGN:
superior colliculus ->
saccadic eye movements
bypass LGN:
pulvinar ->
visual salience (what’s important)
at optic radiations, there is separation of _
superior and inferior fields
optic radiations mneumonic:
SMILe
optic radiations:
Superior fibers travel _
Medially through parietal lobe
optic radiations
Inferior fibers travel _
Laterally through temporal lobe
superior optic radiations (inferior visual field) reach primary visual cortex _ to calcarine fissure
superior
inferior optic radiations (superior visual field) reach primary visual cortex _ to calcarine fissure
inferior
_ fibers swing out creating Meyer’s loop
inferior optic radiations
optic radiations lesion mneumonic:
PITS
(parietal lesion = inferior field defect)
(temporal lesion = superior field defect)
primary visual cortex is characterized by wide layer _
VI
layer VI (primary visual cortex) contains extra band of myelinated fibers, and is called _
striate cortex
the primary visual cortex is organized in _ columns
retinotopic
2 types of cortical columns:
ocular dominance columns
orientation columns
the primary visual cortex is located _
superior and inferior to calcarine sulcus on occipital lobe
majority of LGN fibers _ at V1
terminate
central vision (macula) is represented where in V1?
posterior
peripheral vision is located where on V1?
anterior
optic chiasm lesion, ex pituitary tumor creates what kind of defect?
bitemporal
Ventral stream _ pathway projects to _ lobe responsible for _ lesions cause:
parvo (what)
temporal
color, patterns, shapes
difficulty recognizing objects and deficits in attention to visual cues
Dorsal stream
_pathway
projects to _ lobe
responsible for
Magno (where)
parietal
visual space, navigation thru space
