VISUAL PATHWAY Flashcards
AFFERENT FROM EYES TO BRAIN:
CN II SSA function?
vision and pupillary constriction
CN V GSA function?
Ocular pain
Tearing reflex
Corneal reflex
Proprioception from extraocular muscles
What are the 3 intraocular muscles?
Pupiloconstrictor
Ciliary muscle
Pupilodilator
intraocular muscle that has a sympathetic function? the other two function as ___
Pupilodilator muscle, parasympathetic
Image is inverted in retina, therefore:
Upper visual space to lower retina
Lower visual space to upper retina
Right visual space to left hemiretina
Left visual space to right hemiretina
125 million photoreceptors found within
Light passes through the lens
EYES AND RETINA
Central fixation point of EYES AND RETINA
fovea
Highest visual acuity
Represented by half of the optic nerve fibers and half of the cells in primary visual cortex
fovea
fovea is surrounded by
macula lutea
No photoreceptors
15 degrees medial (nasal) to the fovea
Optic disc
area where Axons of ganglion cells leaving the retina gather to form the optic nerve
Optic disc
Since there is no photo receptors________ has 15 degrees lateral (temporal) and slightly inferior to the central fixation point for each eye
Blind spot
More numerous than cones (20:1)
Relatively poor spatial and temporal resolution of visual stimuli
Rods
Less numerous overall but highly represented in the fovea
Numerous in fovea
High spatial and temporal resolution
Cones
Do not detect colors
Specifically used in night vision as it cannot detect colors
Vision in low-level lighting conditions = night vision
Rods
Detect colors
Visual acuity
Cones
form the outermost layer, farthest from the lens
Photoreceptors
other layers of the retina are not present, allowing light to reach the photoreceptors without distortion
Fovea
the proportion of visual field where light causes excitation or inhibition of the
Area that is stimulated
Receptive field
Photoreceptors respond to light in their receptive field and form excitatory or inhibitory synapses onto ___________
bipolar cells
Bipolar cells synapse with ________________whose axons are sent to the optic nerve
Ganglion cells
Ganglion cells axons becomes the _____________
Optic nerve
Retinal ganglion cells have 2 types:
Parasol cells (A cells)\
Midget cells (B cells)
small receptive field, sensitive to fine visual details and color; project to parvocellular layers of LGB
Midget cells (B cells)
large receptive field, movement and gross stimulus features; project to magnocellular layers of LGB
Parasol cells (A cells)
Horizontal cells
Amacrine cells
Lateral inhibitory or excitatory connections with nearby bipolar and ganglion cells
Interneurons
when bipolar and ganglion cells are excited, surrounding cells are _________
Inhibited
ARRANGEMENT OF VISUAL FIELD
From eyes → optic nerve → optic chiasm → optic tract → LGB → optic radiation → loops around in temporal lobe (Meyer’s Loop) → primary vision cortex
Axons of retinal ganglion cells
Exit via optic canal of sphenoid bone to enter the cranium
OPTIC NERVES
Lesions of eye, retina, or optic nerve produce
monocular visual field defect
Located on ventral surface of midbrain, beneath the frontal lobes and just on top of the pituitary gland
OPTIC CHIASM
Partial crossing of nasal (medial) retinal fibers
Fibers from the left hemiretina of both eyes end up in left optic tract
OPTIC CHIASM
Lesions of optic chiasm often produce
bitemporal (bilateral lateral) visual field defect also called
Lesion on optic chiasm = no vision on
bilateral nasal vision also called Bitemporal hemianopsia
Lesion on optic nerve = no vision on
bilateral temporal vision
Wrap around the midbrain laterally to the LGB of the thalamus
OPTIC TRACT
Lesions posterior to the optic chiasm (optic tracts, LGB, optic radiations, visual cortex)
homonymous visual field defects
or same side
LATERAL GENICULATE NUCLEUS AND EXTRAGENICULATE PATHWAYS:
axons of retinal ganglion cells→ LGB neurons→primary visual cortex
Note: Some fibers bypass the LGB to enter the brachium of the superior colliculus to project to the pretectal area and superior colliculus
After the stimulus goes to the pretectal area and superior colliculus it would go to?
EDW nucleus (PSY)
direct visual attention and visual attention and eye movements toward visual stimuli; project to numerous brainstem areas involved as well as association cortex (lateral parietal cortex and frontal eye fields) via relays in pulvinar and lateral posterior nucleus of thalamus
Superior colliculus and pretectal area
Fan out over a wide area
optic radiation
Axons of LGB enter the white matter to sweep over and lateral to the atrium and temporal horn of the lateral ventricle and then back to the _________________
primary visual cortex
Inferior optic radiations carry information from inferior __________________________
retina (superior visual field)
fibers of the inferior optic radiations arc forward into the temporal lobe
Inferior portion of optic radiation
Meyer’s loop
contralateral homonymous superior quadrantanopia
Temporal lobe lesions
Upper portions of the optic radiation project to the superior bank of the calcarine fissure
contralateral inferior quadrant defects
Inferior optic radiations terminate on the lower bank of the calcarine fissure
contralateral superior quadrant defects
Retinotopically organized
Fovea - represented near the occipital pole
More peripheral regions of ipsilateral and contralateral visual fields are more anterior along the calcarine fissure
PRIMARY VISUAL CORTEX
Lesion on retina with location, size and shape of scotoma depends on the location and extent of the lesion
Monocular Scotoma
Note: If lesion on retina is big enough can cause - monocular visual loss
Retinal disorders
Lesion of optic nerve
Monocular visual loss
Lesion in optic chiasm
If lesion here = both sides ng nasal side will be loss
Pituitary gland tumor, pituitary macroadenoma (enlargement of pituitary gland which can cause^)
Bitemporal Hemianopia
Retrochiasmal lesion - optic tracts, LGN, optic radiation or visual cortex
Homonymous Visual Field Deficit
Lesion of optic tract
Lesion of LGB
Lesion of entire optic radiation
Lesion of entire primary visual cortex
(D, G, H) Contralateral homonymous hemianopia
Contralateral Homonymous Hemianopia
Lesions of temporal lobe through meyer’s loop of lower optic radiation
aka Pie in the sky
Lesion to the lower bank of calcarine fissure
Cannot see on affected lower quadrant side
Contralateral Superior
Quadrantanopia
Lesions of parietal lobe involving the upper portions of the optic radiations
Pie on the floor
Lesions of upper bank of the calcarine fissure
Contralateral Inferior
Quadrantanopia
Partial lesions of visual pathways
Fovea has relatively large representation from the optic nerve to the primary visual cortex
Can occur in the visual cortex due to collateral flow between MCA and PCA
Macular Sparing
Finds, fixates, focuses/aligns on and follows visual targets
foveates
To align each eye to cause the central light to fall on the fovea and the entire retinal image to fall on corresponding retinal points of both eyes
OCULOMOTOR SYSTEM
elevates eyelids, sympathetic (states of sympathetic predominance and static tone or maintenance)
Superior tarsal muscle (Muller’s muscle)
elevates eyelids
Levator palpebrae superioris
controls lens
Ciliary muscles
Activation of ________causing bilateral pupillary constriction and contraction of ciliary muscles of the lens
pretectal nuclei
Activated by visual signals relayed to the visual cortex
ACCOMMODATION REFLEX
Ciliary muscle acts as a _____________
When ciliary muscle contracts, it causes the suspensory ligament to relax, producing a rounder, more convex lens
Sphincter
For near vision
Convergence by medial recti – aims the visual axes onto the near fixation point
Pupillary constriction by pupillary constrictor muscles of the iris (PSY)
Lens thickening by ciliary muscles (PSY)
ACCOMMODATION REFLEX
Lens is normally under tension from
suspensory ligament
PUPILLARY DILATION - SYMPATHETIC
Descending sympathetic pathway→lateral brainstem and spinal cord to T1 and T2.
→Activates preganglionic SY neurons →Axons exit via ventral T1 and T2 ventral roots→paravertebral SY→superior cervical ganglion
→Postganglionic SY fibers →pupillary dilator muscles
Eyelid Elevation
Superior tarsal (Muller) muscle - tonically elevates the eyelid; innervated by carotid sympathetic nerve
Levator palpebrae muscle - tonically and phasically elevate the eyelid; innervated by CN IlI
ptosis, miosis and anhidrosis
Horner’s syndrome
Eyelid Closure
Orbicularis oculi muscle - CN VII
All voluntary horizontal and vertical eye movement
Rapid eye movements in sleep
Bring target of interest into field of view
Vision transiently suppressed
Fast, physiologic = Saccades
allow stable view of moving objects
Smooth pursuit
maintains fused fixation as targets move towards or away
Vergence
rhythmic form of reflex eye movement composed of slow eye movement in one direction, interrupted repeatedly by fast, saccade-like eye movement in the opposite direction
Vestibulo-ocular reflex
Nystagmus
interconnects the CN III, CN IV, CN VI and CN Ill nuclei; eye movements are yoked together for conjugate eye movement in all directions
Medial Longitudinal Fasciculus (MLF)
Responsible for left and right deviation of the eye (horizontal movements)
Paramedian Pontine Reticular Formation (PPRF)
SR, IR, SO and IO
Located in rostral midbrain reticular formation and pretectal area
Vertical eye movements
Ventral portion - _________
Dorsal portion - _________
Rostral interstitial nucleus of MLF - ____________
downgaze, upgaze, mediate downgaze
generate saccades in contralateral direction via connections with contralateral PPRF
Frontal Eye Fields (BA 8)
saccadic brainstem center for vertical eye movements
Rostral interstitial nucleus of the MLF
modulate eye movement
Basal Ganglia
PPRF
Paramedian Pontine Reticular Formation (PPRF)
for smooth pursuit movements in the ipsilateral direction via connections with vestibular nuclei, cerebellum, PPRF
Parieto-Occipito-Temporal Cortex
