VISUAL PATHWAY Flashcards by KIRK IBARRA

AFFERENT FROM EYES TO BRAIN:

CN II SSA function?

vision and pupillary constriction

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CN V GSA function?

Ocular pain
Tearing reflex
Corneal reflex
Proprioception from extraocular muscles

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What are the 3 intraocular muscles?

Pupiloconstrictor
Ciliary muscle
Pupilodilator

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intraocular muscle that has a sympathetic function? the other two function as ___

Pupilodilator muscle, parasympathetic

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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

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125 million photoreceptors found within
Light passes through the lens

EYES AND RETINA

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Central fixation point of EYES AND RETINA

fovea

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Highest visual acuity
Represented by half of the optic nerve fibers and half of the cells in primary visual cortex

fovea

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fovea is surrounded by

macula lutea

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No photoreceptors
15 degrees medial (nasal) to the fovea

Optic disc

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area where Axons of ganglion cells leaving the retina gather to form the optic nerve

Optic disc

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Since there is no photo receptors________ has 15 degrees lateral (temporal) and slightly inferior to the central fixation point for each eye

Blind spot

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More numerous than cones (20:1)

Relatively poor spatial and temporal resolution of visual stimuli

Rods

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Less numerous overall but highly represented in the fovea

Numerous in fovea

High spatial and temporal resolution

Cones

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Do not detect colors
Specifically used in night vision as it cannot detect colors

Vision in low-level lighting conditions = night vision

Rods

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Detect colors

Visual acuity

Cones

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form the outermost layer, farthest from the lens

Photoreceptors

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other layers of the retina are not present, allowing light to reach the photoreceptors without distortion

Fovea

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the proportion of visual field where light causes excitation or inhibition of the

Area that is stimulated

Receptive field

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Photoreceptors respond to light in their receptive field and form excitatory or inhibitory synapses onto ___________

bipolar cells

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Bipolar cells synapse with ________________whose axons are sent to the optic nerve

Ganglion cells

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Ganglion cells axons becomes the _____________

Optic nerve

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Retinal ganglion cells have 2 types:

Parasol cells (A cells)\

Midget cells (B cells)

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small receptive field, sensitive to fine visual details and color; project to parvocellular layers of LGB

Midget cells (B cells)

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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

VISUAL PATHWAY Flashcards

(83 cards)