visual system Flashcards
afferents from eyes to brain
CN II - vision and pupillary constriction
CN V - ocular pain, tearing reflex, corneal reflex, proprioception
efferents of eyes
CN III, IV, VI - ocular muscles
discuss how light and images pass through eyes and retina
light passes through lens and images are inverted and reversed
relate visual spaces to parts of retina
upper - lower retina
lower - upper retina
right - left hemiretina
left - right hemiretina
the central fixation point of each eye is at the ______
fovea
what represents the fovea
half of optic nerve fibers and have of cells of primary visual cortex
the fovea is surrounded by ______
macula
discuss all about the optic disc
area found 15 deg medial/nasal to fovea and has no photoreceptors
hence blind spot found 15 deg lateral/temporal and inferior to the central fixation point of each eye
discuss all about receptive field
receptive field contain photoreceptors that respond to light by forming excitatory or inhib synapses with bipolar cells
bipolar cells synapse with retinal ganglion cells na connected sa optic nerve
discuss the 2 kinds of retinal ganglion cells
parasol or A cells - large receptive field; for movement and gross stim; projects to magnocellular layer of LGB
midget or B cells - small receptive field; sensitive and fine vision and color; projects to parvocellular layer of LGB
discuss all about interneurons
horizontal and amacrine cells
forms lateral inhibitory or excitatory connection with bipolar and ganglion cells
excitation on part of retina with light inhib on surrounding
discuss all about rods
more than cones but poor spatial and temporal resolution; NO COLORS
for low level light - night vision
discuss all about cones
less but high in fovea; high spatial and temporal resolution; YES COLORS
for visual acuity
lesions of eye, retina and optic nerve
monocular visual field defect
lesions to optic chiasm
bitemporal visual field efect
lesions to optic tract, LGB, optic radiations and visual cortex (posterior to optic chiasm)
homonymous visual field defects
discuss lateral geniculate nuc and extrageniculate pathways
LGB project to primary visual cortex but some enter brachium to go to pretectal area and sup coll
pretectal area is for
EDW - pupillary light reflex
sup coll and pretectal is for
direct visual attention and eye movements towards stim
what is Meyer’s loop
fibers of inferior optic radiation goes to temporal lobes
inferior optic radiations carry info from _______
inferior retina - sup visual field
upper portions of optic rad projects to ______
sup bank of calcarine sulcus
temporal lobe lesion
contralateral homonymous superior quadrantanopia
upper optic radiations pass under ______
parietal lobe
parietal lobe lesion
contralateral homonymous inferior quadrantanopia
lesion on calcarine
contralateral superior quadrant defects
discuss visual processing
input arrives at cortical layer 4 of primary visual cortex
sublamin 4A, 4B, 4C alpha and 4C beta
sublamina 4B is aka as
stria of gennari
magnocellular layer of LGB porject to ______
to layer 4C alpha
parvocellular layer of LGB porject to ______
project to 4C beta
parvocellular layer and intralaminar zones porject to ______
project to cortical layers 2 and 3 - for color
purpose of oculomotor system
finds, fixates, focuses/aligns on and follows visual targets - foveates
para light will fall on fovea and retinal image falls on corresponding points = visual acuity and single mental image
discuss pathway for pupillary contriction
light activates ganglion cells - optic nerve - chiasm - tracts - extrageniculate going to pretectal - (B) EDW - ciliary ganglion - ciliary muscles
discuss accommodation reflex
for near vision - by medial recti so aims eyes near fixation point
contsriction also by pupillary contrictors
lens thickening by ciliary muscles
discuss pupillary dilation
Postganglionic SY fibers ascend through carotid plexus along the walls of the ICA to cavernous sinus, ultimately reaching the pupillary dilator muscles
discuss saccades
REM or basta fast vertical or horizontal eye movement
vision transiently suppressed; brings target in field of view
discuss smooth pursuit
allow stable view of moving objects
retino-geniculo-occipito-parieto-frontaltegmental pathway
discuss vergence
maintains fused fixation as targets move towards or away
retino-geniculo-occipito-tegmental pathways
discuss nystagmus
slow eye movement towards wanted direction tas fast movement in opposite
vestibulo-ocular reflex
discuss fixation system
holds the eyes on the target and promote fusion of both retinal images into one sharp image
retino-geniculo-occipito-tegmental and retinooccipito-fronto-tegmental pathways
discuss brainstem circuit for horizontal eye movement
by LR and MR - MLF interconnects CN III, IV, VI and CN III nuc for conjugate eye movement in all directions
discuss voluntary horizontal eye movements
paramedian pontine reticular formation send fibers to ipsi abducens nuc that sends to ipsi LR and contra MR
stimulation of right PPRF or right abducens will make the eyes deviate conjugately to the right
discuss brainstem circuit for vertical eye movement
by SR, IR, SO and IO
loc in rostral midbrain reticular formation and pretectal area
for mediate downgaze
Rostral interstitial nucleus of MLF
Conjugate upward eye movement
tegmentum dorsal downward pathway
Conjugate downward eye movement
tegmentum dorsomedial to red nucleus
saccadic brainstem center for vertical eye movements
Rostral interstitial nucleus of the MLF
brain stem center for horizontal saccades
PPRF
discuss role of frontal eye fields or BA 8
generate saccades in contralateral direction via connections with contralateral PPRF
discuss role of parieto-occipito-temporal cortex
for smooth pursuit movements in the ipsilateral direction via connections with vestibular nuclei, cerebellum, PPRF
Cortical descending control of eye movements is heavily influenced by visual inputs arriving at the _____
primary visual cortex and visual association cortex
modulates eye movements
basal ganglia
