Visual System Flashcards
1
Q
Visual System
A
2
Q
Vision
A
- Very large area devoted to this sense in humans.
- Light passes through cornea > pupil > lens forms inverted & reversed image on the retina.
- Where the optic nerve enters the retina, no rods or cones, creates the optic disc which is the blind spot.
- Not superimposed so no functional blind spot.
3
Q
Vision
A
- The fovea is the area of central fixation; region of highest visual acuity (highest amount of receptors).
- The macula surrounds the fovea, also high visual acuity.
4
Q
Optic Field of View
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5
Q
Photoreceptors
A
- Rods.
- More numerous; 20:1.
- Do not detect colors & good for low light.
- Cones.
- Lots in the fovea.
- Can see color.
6
Q
Receptive Field
A
- Receptive field of a neuron in visual pathway: portion of visual field where light causes excitation or inhibition on bipolar cells.
- Bipolar cells synapse onto ganglion cells that send axons into the optic nerve which exits through optic canal of sphenoid.
7
Q
Optic Diagram
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8
Q
Optic Nerve, Chiasm, Tract
A
•Some fibers from the optic nerve cross over at the optic chiasm.
9
Q
Lateral Geniculate Nucleus (LGN) & Extrageniculate Pathways
A
- Axons of retinal ganglion cells in optic tract synapse of the LGN of the thalamus.
- Continue to the primary visual cortex via optic radiations.
- Few fibers bypass LGN & enter brachium of superior colliculus (this is extrageniculate pathway).
- Relay to pretectal & superior colliculus go to Pulvinar > temporo-Parieto-occipital association love.
10
Q
Figure 11.6 Geniculate and Extrageniculate Visual Pathways
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11
Q
Optic Radiations to Primary Visual Cortex
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- Axons leave LGN (“C” shape around lateral ventricle) to go to primary visual cortex by Calcarine fissure.
- Called optic radiations.
12
Q
Primary Visual Cortex
A
- Upper portions à superior bank of calcarine fissure.
- Lower portions à inferior bank of calcarine fissure.
- Upper bank lesions:
- Contralateral inferior quadrant defects.
- Lower bank lesions:
- Contralateral superior quadrant defects.
- Fovea: 50% of visual cortex.
13
Q
Left visual hemifields of the left and right eyes mapped to the primary visual cortex of the RIGHT hemisphere.
A
14
Q
Visual Processing in Neocortex
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- Most input arrives in layer 4.
- Thick layer due to functional importance.
- Subdivided into sub-laminae 4A, 4B, 4C α, and 4C β.
- Layer 4B has a lot of myelinated axon collaterals forming pale looking stria of Gennari can be seen in the gray matter with naked eyeball.
- Primary visual cortex (AREA 17) sometimes called striate cortex.
15
Q
Primary Visual Cortex
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17
Q
Some Terms to Describe Visual Disturbances
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21
Q
Figure 11.15 Effects of Lesions in the Primary Visual Pathways
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