Visual System Flashcards
horizontal gaze (right) steps
L cortex FEF activated
R pontine gaze center @ paramedian pontine reticular formation (PPRF)
R abducens nuc (synapse on 2 things)
1. abducens (VI) contract R lateral rectus muscle
2a. cross midline, along medial longitudinal fasciculus to oculomotor nuc in midbrain
2b. occulomotor (III) contract L medial rectus muscle
lesion to abducens nerve
stop ipsilateral abduction
R lesion, R eye can’t abduct
lesion to abducens nucleus
bilateral inability to look towards lesion (abduct ipsi, adduct contra)
lesion to PPRF
bilateral inability to look towards lesion (abduct ipsi, adduct contra)
abducens nuc lesion complications
may have ipsi facial paralysis (VII loops around nuc)
lesion MLF
internuclear opthalmoplegia
contra eye cannot adduct (for conjugate)
convergence in tact (EdWest still ok)
ipsi eye has nystagmus
differentiate MLF vs III lesion
cannot adduct but can elevate –> III in tact
convergence is intact –> III in tact
lesion cerebral cortex (primary visual - FEF)
neither can look to contra side (R lesion, can’t look L)
slow drift to ipsi side (R lesion, drift R)
complications of primary visual cortex lesion
FEF close to RUL motor cortex
may have RUL weakness
aqueous humor path
secreted by ciliary bodies into post chamber go thru pupil circulate in ant chamber taken up by canal of schlemm go to venous system
glaucoma mech
problem draining aqueous humor –> intraoccular P builds up –> optic disc cupping - affect longest nerves first (lose peripheral vision)
light reflex (constriction) steps
- light stim optic nerve
- optic n stim pretectum (in midbrain)
- stim both EdWest nucs
- both pregang para III synapse in ciliary ganglia
- both postgang para stim pupillary constrictor muscle
- pupil constricts (miosis)
neurosyphilis and light reflex
affect pretectum
stop pupillary light reflex bilaterally
near response in tact
(Argyll Robertson pupil)
pineal tumor and light reflex
compress pretectum
stop pupillary light reflex bilaterally
near response in tact
(Argyll Robertson pupil)
light reflex (dilation) steps
hypothalamus DHF T1 superior cervical gang pupillary dilator muscle
events of near response
accommodation
convergence
pupillary constriction
accommodation steps (in near response)
para fibers contract ciliary muscle (relax suspensory ligs - become rounder)
ciliary muscle actions
contract: relax suspensory ligs - lens becomes rounder - see things close
relax: contract suspensory ligs -lens become flatter - see things far
convergence (in near response)
III innervates both medial rectus muscles –> adduct both
near response steps
stim visual cortex superior colliculus and pretectal nuc EdWest oculomotor nuc (+ ciliary gang) III adducts both (medial rectus) (+ para constricts pupils, contract ciliary muscles)
Argyll Robertson pupil causes
neurosyphilis
pineal tumor
diabetes
Argyll Robertson pupil Sx
no direct or consensual light response
near response in tact
Argyll Robertson mech
lesion/compress pretectum
more neurons devoted to near than light response
Argyll Robertson AKA
pupillary light-near dissociation
prostitute’s pupil
Marcus Gunn pupil AKA
relative afferent
Marcus Gunn mech
optic nerve lesion
Marcus Gunn causes
MS
Marcus Gunn Sx
light in affected pupil - pupils dont constrict fully
light in unaffected - pupils constrict fully
light in affected again - pupils dilate (weaker stim in II)
Transtentorial (uncal) herniation cause
increased intracranial pressure
Transtentorial (uncal) herniation mech
increased intracranial P –> uncal herniation –> CN III compressed –> affect para, add/elevate muslces, LPS
Transtentorial (uncal) herniation sx
pupil fixed and dilated (1st)
down and out eye
ptosis
horner syndrome mech
lesion of oculosymp pathway
horner syndrome sx
miosis (lesion side)
ptosis
apparent enopthalmos
hemianhidrosis
Adie pupil mech
ciliary gang lesion
affects highly myelinated DRGs in LL too
Adie pupil sx
monocular AR pupil (dilated pupil responds sluggishly to light but responds to near response)
loss of knee jerk reflex (on side of lesion)
fovea location, description
post temporal side of retina
cones only - direct access to light
age related macular degeneration mech
push macula away from choroid (can’t get nutrients) –> lose macular/central vision
layers of retina (in to out)
ganglion cell layer
bipolar cell layer
photoreceptors
pigment epi
amacrine cell fxn
synapse w/ ganglion and bipolar cells
detect motion speed and light intensity
horizontal cell fxn
enhance contrast
rods (kinds, fxn)
1 kind
black/white
low-light sensitive
night vision, motion
cones (kinds, fxn)
3 kinds
red, green, blue
bright light only
object recognition (edges)
visual processing steps (in retina)
rods/cones stim by light stim bipolar cells (less) stim ganglion cells (even less) axons of gang cells make up optic nerve (II) LGB
vision steps
- retina (II) stimulated (by opp field)
2a. temp/lat II stay ipsi
2b. nasal/med go contra via optic chiasm
3abc. branches to hypothalamus, pretectum and sup colliculus - go to LGB
5a. upper field go up thru parietal to cuneate gyrus of cortex
5b. lower field go down thru temporal via meyers loop to lingual gyrus of cortex
lesions in front of chiasm (types)
optic nerve
11/2 optic nerve (temp or nasal)
lesions in front of chiasm (qualities)
monocular
ipsilateral
defect from lesion of optic nerve
no vision in ipsilateral eye (anopia)
defect from lesion of 1/2 optic nerve
temporal lesion –> no nasal vision in ipsilateral eye
nasal lesion –> no temporal vision in ipsilateral eye
optic nerve lesion causes
internal carotid artery aneurysm
chiasm lesion qualities
binocular
bitemporal vision loss (only nasal IIs cross)
heteronymous
lesions in front of chiasm (causes)
optic neuritis
central retinal artery occlusion
superior compression of chiasm cause
craniopharyngioma
superior compression of chiasm mech and sx
upper quadrant of retina is superior (compressed first)
begin as inferior quadrantanopia
inferior compression of chiasm cause
pituitary adenoma
inferior compression of chiasm mech and sx
lower quadrant of retina is inferior (compressed first)
begin as superior quadrantanopia
lesions past chiasm types
optic tract to LGB
meyer loop
parietal loop
cerebral cortex
lesions past chiasm qualitites
binocular
contralateral
homonymous
defect of optic chiasm lesion (whole)
bitemporal heteronymous hemianopia
can’t see on outside
optic tract lesion mech
lesion ipsilateral temporal retina
lesion contalateral nasal retina
defect in optic tract lesion
contralateral homonymous hemianopia
meyer’s loop lesion mech
lesion ipsi lower temporal retina
lesion contra lower nasal retina
meyers loop lesion defect
contra homonymous superior quadrantanopia
parietal tract lesion mech
lesion ipsi upper temporal retina
lesion contra upper nasal retina
parietal tract lesion defect
contra homonymous inferior quadrantanopia
cerebral cortex defect
contra homonymous hemianopia w/ macular sparing (sep. blood flow)
lesion both tracts from LGB mech
lesion ipsi temporal
lesion contra nasal
lesion both tracts from LGB defect
contra homonymous hemianopia
