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22 Cards in this Set
- Front
- Back
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visual field components |
- binocular zone - broad central region - monocular crescents - only ipsilateral eye - quadrants of visual field: o hemifields (left/right) o quadrants (upper/lower) |
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visual field entering the eye for processing - retinal/receptive field |
- lens inverts and reverses the projection of the visual field on the retina - quadrants: o divided into nasal and temporal, inferior and superior |
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right visual hemifield object projected to receptive field |
- projected onto nasal ipsilateral receptive field - projected onto temporal contralateral receptive field - same for the left visual hemifield |
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optic chiasm decussation |
- axons from nasal hemiretinal (ipsilateral) cross at optic chiasm to meet the contralateral temporal hemifield - so all the visual information for the original eye are all in the contralateral tract after the optic chiasm |
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primary visual termination of optic tract |
- lateral geniculate body (posterior margin of thalamus) - 90% of axons terminate here from visual tract - 10% of axons continue to 1. pretactile nuclei (preganglionic sympathetic fibers to ciliary with CN III), 2. superior colliculus in midbrain (projects back to the pulvinar in thalamus for reflex pathway) 3. hypothalamus (suprachiasmatic nucleus) |
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lateral geniculate body |
- 6 layers of neurons - layers 1, 2 = magnocellular layers (M-ganglion cells); - layers 3-6= parvocellular layers (P-ganglion cells); central visual field input ipsilateral = 2,3,5 contralateral = 1, 4, 6 |
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M ganglion cells size retina location input source best response conduction color sensitivity projection in LGB |
size: large retina location: peripheral input source: rods best response: high contrast, movement conduction: large, fast color sensitivity: insensitive projection in LGB: layers 1, 2 |
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P ganglion cells size retina location input source best response conduction color sensitivity projection in LGB |
size: small retina location: central input source: cones best response: fine detail conduction: slow color sensitivity: sensitive projection in LGB: 3-6 |
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optic radiation |
- pathway of LGB to the visual cortex via the lingual gyrus of the primary visual cortex (retino-top map) - binocular portion = above calcarine sulcus - monocular portion = above and below calcarine sulcus |
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complete transection of optic nerve |
- total blindness of ipsilateral eye |
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lesion of optic chiasm |
- bitemporal heteronymous hemianopsia - lose information in lateral regions bilaterally |
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complete destruction of optic tract |
- homonymous hemianopsia - visual information lost from contralateral visual field |
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lesion of optic radiation at Meyer's Loop |
- superior quadrantanopsia - contralateral "pie in the sky" |
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lesion of optic radiation |
- homonymous hemianopsia - loss of contralateral visual hemifield |
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primary visual cortex (V1) |
- 6 layers; striate cortex - LGB axons terminate in layer 4 (thick layer) - convergence of input from LGB to neurons in layer IV - segregation of eyes is maintained in layer IV |
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dorsal/M-pathway |
- M-ganglion cells of retina to the M-layers in LGB to layer IV of V1 - continues as the dorsal pathway - terminates in superior parietal cortex (SPC) - large receptive fields - high temporal resolution - moving/changing stimuli - low spatial resolution |
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ventral/P-pathway |
- P-ganglion cells of retina to P-layers in LGB to layer IV of V1 - continues as ventral pathway - terminates in inferior temporal cortex (ITC) - small receptive fields - low temporal resolution - high spatial resolution - object recognition, perception, memory, color |
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visual agnosia |
- inability to recognize/identify objects/persons without loss of visual acuity |
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simultanagnosia |
- M-dorsal pathway lesions - inability to perceive more than one object at a time in the visual field - usually bilaterally in superior parietal cortex |
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akinetopsia |
- M-dorsal pathway lesions - loss of motion perception ("motion blindness") - life is like a strobe light |
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prosopagnosia |
- P-ventral pathway lesions - inability to recognize faces (prosopon=face) ("face blindness") - can identify features, but can't get comprehensive picture |
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cortical color blindness (achromatopsia) |
- P-ventral pathway lesions - loss of color vision despite normal functioning cones |
