Lec 9 Vision Flashcards
At the chiasm, what % cross? What % continue ipsilaterally?
60% cross.
40% ipsi.
Why do only some cross at the chiasm?
important for binocular vision & depth perception
Optic Tracts project where? (4)
Lateral Geniculate (thalamus) Suprachiasmatic Nucleus (hypothal) Pretectum Superior Colliculus (midbrain)
Lateral Geniculate projects where?
optic radiations, then to primary visual cortex (V1)
primary visual cortex = brodmans area ___
17
Ventral pathway of primary visual cortex projects where?
temporal lobe
Dorsal pathway of primary visual cortex projects where?
parietal lobe
Retino-hypothalamic path functions
circadian rhythm
ANS response
Pretectum function
pupillary reflex
Pretectum projects where?
Edinger-Westphall (midbrain)
Edinger-Westphall PRE-ganglionic projects where?
CN 3 -> ciliary ganglion (lens accom)
Edinger-Westphall POST-ganglionic projects where?
sphincter pupillary muscle
Superior colliculus function
coordinate head/eye movements
Pupillary direct response
stimulated eye constricts
Pupillary consensual response
contralateral (un-stimulated) eye also contracts
Axons from the Nasal retina ____ in the chiasm (cross/stay on same side)?
cross
Axons from the Temporal retina ____ in the chiasm (cross/stay on same side)?
stay on same side
Left visual field: which nasal retina, which temporal retina, which optic tract?
- *Left** nasal retina
- *Right** temporal retina
- *Right** optic tract
Right visual field: which nasal retina, which temporal retina, which optic tract?
- *Right** nasal retina
- *Left** temporal retina
- *Left** optic tract
Meyers loop: where is it, what part of visual field does it view?
inferior Lateral Geniculate.
superior visual field.
Superior Lateral Geniculate views what part of the visual field?
inferior
Anopsia vs. Scotoma
Anopsia = large deficit Scotoma = small deficit
Damage at A
complete loss of R visual field
Damage at B (Chiasm)
Bitemporal Hemianopsia
loss of fibers crossing (from both nasal retina) = loss of both temporal fields.
Damage at C (Optic Tract)
Left Homonymous Hemianopsia.
loss of fibers from R temporal & L nasal = loss of R nasal field + loss of L temporal field
Damage at D (Optic Radiations)
Superior Homonymous Quadrantopsia.
loss of fibers from R superior temporal & L superior nasal = loss of L temporal + R nasal superior fields
Damage at E (Primary Visual Cortex)
Homonymous Hemianopsia w/ Macular Sparing
unknown mechanism
Role of extraocular musc
Foveation: direct fovea towards object of interest
Lat/Med Rectus actions
horizontal movements (ABD/ADD)
Sup/Inf Rectus actions
vertical movements (elev/depress)
Sup/Inf Oblique actions
Intorsion: top of eye toward nose.
Extorsion: top of eye away from nose.
Elevation force couple
Sup Rectus
Inf Oblique
Depression force couple
Inf Rectus
Sup Oblique
Vestibulo-Ocular Reflex (VOR)
when head moves, eyes move the same distance/speed in OPPOSITE direction
Why are saccadic movements considered “ballistic”
cannot respond to changes in target position once already started. If a target moves during a saccade, a second saccade must be generated.
Amplitude of saccades
duration of neuron activity (freq of APs)
Direction of saccade is governed by
2 gaze centers in Reticular Formation
- PPRF
- Rostral Interstitial Nucleus
PPRF = ____ (horizontal/vertical) movements
horizontal
Rostral Interstitial Nucleus = ____ (horizontal/vertical) movements
vertical
What happens once PPRF is activated?
Activates ipsi Abducens, which activates LMNs (to ipsi Lat Rectus) and Internuclear neurons (to contra Oculomotor = Med Rectus)
L PPRF is activated by
R frontal eye field
R superior colliculus
