central visual pathways Flashcards
How is the visual field bisected?
into left and right sides
What happens to the left and right sides of the visual field?
each is projected to the opposite side of the brain.
how is the visual field sent to opposite sides?
partial decussation of ganglion cells, visual fields project to opposite lateral geniculate body
Where does visual field decussation happen?
optic chiasm
What part of the visual field goes to both sides of brain?
fovea of retina, center of visual field
What symptoms if you has lesion from one optic nerve?
total blindness in one eye, information would still go to both sides of brain from other eye
What is hemianopsia?
loss of half of visual field
two types of hemianopsia?
heteronymous and homonymous
Heteronymous is what?
tunnel vision, loss of opposite visual field due to optic chiasm lesion
Homonymous is what?
loss of same side visual field, optic tract lesion on way to LGN
Where do the parvocellular and mangnocellular pathway got to and from?
Retina - LGN - Cortex pathway
Cells of the parvocellular path?
midget- cones
Cells of magnocellular path?
Parasol - rods
Explain parvocellular path
Color, high resolution, slow, sustained
Expain magnocellular path?
monochrome, low resolution, fast, transient
How are the parvo,magnocellular pathways orientated?
Parallel paths LGN then cortex
What path for object perception and ID?
parvocellular
What path for motion, direction, alerting, etc?
magnocellular
What type of cells are the parvo and magnocellular cells?
they are the specialized types of ganglion cells
What type of specialized ganglion cell are there more of in optic nerve?
There are more parvocellular, midget cells, 95 percent
What type of specialized ganglion recieves information from the larger group of bipolar,photoreceptor cells?
Magnocellular,parasol cells, about 5 percent of axons in optice nerve
Does parvo or magnocellular have the largest center surround?
Magnocellular has the large center surround receptive fields cuz it has more photoreceptors
How is the LGN arranged and what does that have to do with the parvo,magnocellular pathways?
LGN has 6 layers, the magno,parvo send their info to different layers.
where is the primary visual cortex (VI)?
medial surface of occipital lobe.
How are the association visual areas, V2,3,5 arranged?
in concentric cortical areas around primary visual cortex
From what cells does Primal visual cortex develop perception of form, color and directon?
From the activity of simple and complex cells
The simple and complex cells that give VI info are arranged how?
in columns so that they can respond to certain bars,orientations of light.
What does a simple cell do?
Combine info from LGN cells, Respond to bars of light in specific orientations
What do complex cells do, where do they get their info?
Respond to bars of light in specific orientation, they get info from many simple cells
Do simple or complex cells respond to edges?
the simple cells respond to edges
What cells detect position and orientation of structure?
complex cell
What does hypercomplex cell do?
Detect endpoints and crossing lines
What cortex integrates simple, complex and hypercomplex cell info?
Secondary association cortex integrates information to generate sense of familarity of objects
Large receptive fields are sensitive to what?
sensitive to low spatial frequencies
What properties do visual cortical columns sort info into?
edge orentation, color, size, shape, direction, ocular dominance
What cells do visual cortical columns use to sort info?
simple and complex cells
How are visual vortical columns arranged?
vertical zies of cortex
What are “blobs”
Regions of cortex that Color opponent center surrounds RFs are sorted into
what to blobs process?
relative activities of color cells to form perceptial pallate.
what cortal area are blobs within?
withinvisual cortical columns
Complex cells in what layers of cortices generate depth perception?
complex cells in upper and lower layers of primary and association cortices.
can you get depth perception with just one eye?
yes but its by using visual cues
How is binocular depth perception determined?
retinal disparity and eye convergence
What is used to provide feedback onto sensory pathways?
complex activity generated by the cortical columns
What modulates LGN cells?
Brain stemp pathways using NE, AcH, NO
Cortical feedback to LGN shaes sensory input according to what?
behavior of the organism
What makes responses to light more discrete in the LGN?
cortical feedback, makes more difference between bars of light.
RF is what?
receptive field
What can enhance the LGN cortical transmission of stimulus?
cortical cells that respond optimally to particular receptive fields of light.
What chemical will enhance transmission of visual info by stimulating LGN and cortex?
NO and Ach that is released from the brain stem
No comes from where?
reticular foramen
Intense emotions can cause what of LGN?
seeing flashes of light.
What can modulatory activity do in LGN?
shift between arousal and sleep, waking up thalamus for attention
What stream is parvocellular stream?
The Ventral “what” stream is parvocellular, cones toward the temporal lobe
What stream is the magnocellular stream?
the Dorsal “where” stream is magnocellular, rods tword parietal.
The ventral stream is transmits infro from what area of retina?
the fovea, cones for acuity
The dorsal where stream transmids info from what area of retina?
From the peripheral retina, rods for action to answer how and where
Both the ventral and dorsal stream end up at the prefrontal cortex to do what?
converge to make working memory
Vi cortex projects what to association cortices?
orientation, spatial frequency, color
Why does VI project info to association cortices?
for integration into objects.
V2 is for what?
angles, illusiory contours, ground or figure
V4 is for what?
color and comlex shape, corners
Iferotemporal cortex is for what?
scale and position invariance, Faces
Middle temoral is for what?
Part of dorsal stream for detecting complex global motion
Inferotemporal cortex, IT responds to both halfs of visual field via what?
corpus callosum via interhemispheric axons
what does Inferotemporal neurons respond to?
complex shape,color, facial image, emotional expression
What part cortex is responsible for d?j? vu?
inferotemporal cortex
What can modify both long and short term memory for visual stimuli?
Modified by experience, impacted by hippocampus, amygdala,
What are the hippocampus and amygdala responsible for?
Limbic structures responsible for consolidating memories into cortex
What can modity activity of IT, inferotemporal cortex neurons?
attention, focus and you notice it more
What is visual neglect syndrome?
Loss of funciton in half of the visual association cortices
What is responsible for face recognition with emotional valence?
fusiform gyrus, faster than conciousness
What can fusiform gyrus cause if it malfunctions?
hallucinations
Synesthesia is what?
hereditary condition where experience different modalitys simultaneously, color numbers
Possible causes of synesthesia?
cross activation of neurons in fusiform gyrus
what are secondary visual pathways responsible for?
non concious visual responses and behavior
Where do ganglion cells project for secondary visual pathway?
Konicellulary to superior colliculus, melanopsin to pretectum and superchiasmic nucleus
Superior colliculus is for what?
visual orientatio, saccades, blindsight, emotion
Pretectum is for what?
pupillary reflex
superchiasmic nucleus is for what?
circadian fhythms
What ganglion cells for circidian rhythem and pupillary reflex?
melanopsin ganglion cells to pretectum and suprachiasmic nucelus
What ganglion cells for blindsight, emotion, saccades and visual orentation?
konicelluular to superior colliculus
Does konicellular ganglion have center surround fields?
nope, it has large receptive fields,
Where does superior colliculus pathway receive input from?
Konicellular ganglion, visual , auditory, association and motor areas of cerebral cortex
Where does superior colliculus pathway project info to?
saccaes eye movement areas, brain stem and spinal cord for head turning
what is the main function of superior colliculus pathway?
orient head and eyes to visual stimulus, where is it?
Saccaes are what?
quick, simultaneous movements of both eyes in same directions.
what directs saccadic eye movements?
cortiical eye field or superior colliculcu
Superior colliculus modulates what cranial nerves?
III, IV, VI
two sypes of saccades?
reflex - exogenously triggered, scanning - endogenous
when does seeing occur?
only between pauses of saccadic eye movement
what can cause blind sight?
lesion of primay visual cortex
what is blind sight?
lack of consciousness of visual information, but can still track, grasp point
what generates blind sight?
extrastriate midbrain pathway, visual input is directed to parietal areas to dorsal stream only
What system may explain blindsight phenomenon?
primitive visual system
Visual emotion pathway
konicellular - superior colliculuc - pulvinar of thalamus-amygdala - cingulate - orbitofrontal cortex
what does the pulvinar of visual emotional pathway do?
convey aversive emotional stimuli to amygdala, cingulate, aond orbitofrontal cortex.
Wht does amygdala do for visual emotional path?
Stimelates pathway for mental arousal and awarness.
Is the visual emotional pathway available in blindsight?
Visual emotional pathway is seen in blindsight
Externally perceved things involve activation of what?
activation of specialized visual areas
Internall percieved thing involve what?
activation of mostly frontal nad parietal areas
What is charles bonnet or deafferentations syndrome?
causes hallucinations from increased activity in fusiform face area or color center
What deficiency can maybe cause visual hallucinations?
cholinergic and serotonergic deficiency
What are the two levels of altered neural activity that cause hallucinatios?
activation of specific cortex or intercordical connections , neuromodulation of cortical areas by cholinergic and serotonergic paths from reticular formation.
Loss of cholinergic and serotonic inputs results in what type of hallucination?
more complex
What do intrinsically photosensitive retinal ganglion cells do?
mess with circadian rhythems because they absorm mostly blue light.
What nucleus has something to do with circadian rhythems?
suprachiasmatic nucleus
What type of ganglion cells project to SCN, suprachiasmic nucleus?
melanopsin ganglion cells,
what entrain SCN activity?
light and dark cycles
what does PVN, paraventricular hypothalamic nuclei affect after being affected by suprachiasmic axons?
sympathetic and parasympathetic systems, hypothalamic release of reproductive and stress hormones.
What do neurons in suprachiasmic nucleus specifically target?
peripheral clocks, pacemakers in skin, liver, pineal, adrenal etc.
What regluates release of melatonin?
SCN regulates pineal release of melatonin via SNS
what does melatonin regulate?
sleep wake cycle, temp, cortisol release, some organs.
when is melatonin released?
with decrease in light, it promotes sleep
what is pupillary light reflex for?
maintain right level of light into eye
what nuclei does the melanopsin ganglion cells activate?
pretectum, edinger-westphal nuclei in midbrain.
what does pretectal nucleus do?
coordinates both eyes, pupillary constriction
what activity increases light entry into eyes?
sympathetic activity
what muscle raises upper eyelid in response to Sympathetic activity?
tarsal muscle.
What activates dilator pupillae?
postganglionic superior cervical ganglion cells
what controls eyelid and iris dilation?
sympathetic control both locally and descending from limbic and hypothalamus
Horners syndrome?
drooping eyelids, ptosis, caused by damage to some aspect of SNS
