Visual pathways Flashcards
describe the path for when enters light –> occipital lobe xx
ganglion cells in retina have axons that project down optic nerve
two optic nerves meet at the optic chiasm
the axons pass through the optic chiasm and form the optic tract
go to lateral geniculate nucleus and go to occipital lobe
concious visual pathway is mediated by which pathway? [1]
after synapse for concious visual pathway has gone to brodmann area 17, where does it go next? [1]
concious visual pathway is mediated by which pathway? [1]
lateral geniculate-occipital pathway
after synapse for concious visual pathway has gone to brodmann area 17, where does it go next? [1]
visual association pathway: (areas 18 & 19) - where the data from the retina is converted in concious perception
which part of the brain gives you the ability to track an object? [1]
what does ^ connect with?
which pathway mediates neck flexes triggered by seen objects? [1]
which part of the brain gives you the ability to track an object? [1]
superior colliculi
some optic nerve fibres go to the superior colliculi -> connects to the medial longitudinal fasciculi (MLF): links together and synchronises the oculomotor nuclei
which pathway mediates neck flexes triggered by seen objects? [1]
tectospinal tract
= together give synchronised eyes and neck movement
how could eyes look like they’re seeing something / following something but actually nothing is being seen?
lesion in visual perception could occur, but not in the visual tracking and fixation area
objects in left visual field go to which visual cortex? [1] in right and left eye?
describe the pathway info goes if looking at something in left visual field from right and left eye?
left visual field –> right visual cortex (& vice versa)
if seeing something in the left visual field:
left eye
pass through lens & stimulate the photoreceptors in nasal hemiretina in left eye. ganglion cell axons project out of optic nerve & cross over in optic chiasm; end up synapsing on lateral geniculate nucleus on right hand side
right eye
left visual field stimulates temporal hemiretina & stays on same side in optic chiasm go to lateral **geniculate nucleus on right hand side
both then go to right visual cortex**
describe how eyesight is affected from each lesion
1: partial optic nerve lesion - ipsilateral scotoma = partial blind spot in eye easy to be unaware !
2: complete optic nerve lesion = complete blindess in that eye
3: optic chiasm lesion = bitemporal hemnianopia - cant see in lateral side of both eyes
4: optic tract lesion = homonymous hemianopia - cant see lateral on one side & medial on the other
5: damage to meyers loop = upper left visual field loss
what would you see / not see in 6-8?
- optic radation lesion: homonymous hemianopia with foveal sparing - there is macula sparing bc of axons on other side of brain
7 visual cortex lesion in inner cortex: homonymous hemianopia (very similar to above)
8: visual cortex lesion in superfial striate cortex (central area 17): bilateral loss of macula vison
visual reflexes are mediated by which CNs? [3]
which is the only CN to emerge from the dorsal surface of brainstem? [1]
visual reflexes are mediated by which CNs? [3]
oculomotor nerve (CN3)
trochlear nerve (CN4)
abducens nerve (CN 6)
which is the only CN to emerge from the dorsal surface of brainstem? [1]
trochlear nerve (CN4)
explain the mechanism of the pupillary light relfex?
in on II out on III
(afferent: optic nerve, efferent: oculomotor nerve)
mechanism:
- activation of photoreceptors stimualtes optic nerve fibres. some dont go to the lateral geniculate but instead to superior colliculus & pretectal nucleus
- from pretectal nucleus there is bilateral projection to at **Edinger-westphal nuclei
-**
fibres leave Edinger-westphal nuclei & synapse at ciliary ganglia in orbit behind each eye
- from here, postganglionic fibres entre the eye and act on sphincter muscles around pupil to constrict it.
-
what would the following be caused by?
- stimulate one eye & no response in other eye: [1]
- constriction in stimulated eye but no constriction in the other: [1]
- constriction in other eye but no respnse in stimulated eye: [1]
- stimulate one eye & no response in other eye: midbrain oculomotor nuclei damage
- constriction in stimulated eye but no constriction in the other: oculomotor damage in other eye
- constriction in other eye but no respnse in stimulated eye: ocuolomotor damage in stimulated eye
which brodman area corresponds to accomodation reflex? [1]
what are the 3 parts of the reflex? [3]
which brodman area corresponds to accomodation reflex? [1]
area 8 !
what are the 3 parts of the reflex? [3]
thickening of lens
convergence
pupil constriction
accomation reflex:
- explain how thickening of the lens occurs xx
what happens to lens in old age?
_accomodation reflex:
a) thickening of the lens_
far object
- ciliary muscle sphincter is relaxed, lens is under tension from suspension ligaments: lens is flat
near object:
- ciliary muscle sphincter is contracts, suspension ligaments become slack: lens is fat
(what happens to lens in old age?
lens doesnt move cuz its hardened / still - cant see stuff close (need reading glasses))
b) convergence of eyes:
- CN III bilaterally causes medial rectus muscles to contract & relaxation of the lateral rectus muscles
c) pupil constriction:
(outlined before - same as pupillary light reflex)
- improves foucssing on objects
accomodation reflex:
b) how does convergence of eyes occur?
accomodation reflex: how does convergence of eyes occur:
- CN III bilaterally causes medial rectus muscles to contract & relaxation of the lateral rectus muscles
vestibulo-ocular reflex - what does this allow? [1]
which is the afferent CN? [1]
which is the efferent CN? [2]
vestibulo-ocular reflex - what does this allow? [1]
head changes angle, eyes compensate for movement & keep gaze steady
which is the afferent CN? [1]
vestibulo-cochlear (VN III)
which is the efferent CN? [1]
**abducens (CN VI): drives the lateral rectus muscle
CN III: drives the medial rectus muscle
mediated by: medial longitudinl fasiculus**
