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41 Cards in this Set

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refracts light to project image onto retina


helps refract light, focus image on retina

Go over steps of visual processing

use slides

Two main portions of the retina

nasal fields and temporal fields

Nasal fields

interior of the retina, closer to nose, projects contralterally

Temporal fields

outer portion of retina, close to ears, projects ipsilaterally

Three layers of retina

1) photoreceptors - rod and cones

2) intermediate neurons

3) optic nerve fibers


rods and cones


no color, dim light, outside fovea, low acuity

Do not fire AP


color, bright light, inside fovea, high acuity

Do not fire AP

Each cone has one of three classes of pigments, with each responding a a range of wavelengths


where visual processing begins, has three layers, contains ~100 million photoreceptors, visual system updates ~ 3 times/sec based on photorecptor activity

Visual processing from the retina in terms of projections

Rod and cones project to bipolar cells which project to ganglion cells whose axons form the optic nerve. There are also intermediate neurons that provide more processing through lateral inhibition.

Horizontal cells - by the photoreceptor/bipolar synapse

Amacrine cells - by the ganglion synapse

Bipolar cells

Receive projections from the rod/cones.

Do not fire AP

Ganglion cells

receive projections from the bipolar cells, and conduct AP, make up the optic nerve


Sharpness of vision

Great in the middle of the visual field, but falls off towards the perihpery

Highest in fovea


central part of visual field; directly behind the pupil so there is less blood in front of it, therefore more light reaches it.

Contains the highest density of cones

SO: this is area of highest acuity


a photopigment that captures photons, selectively, at different wavelengths.

Two parts: retinal and opsin

Different cones captures different colors of light

visible light of spectrum is between

400 - 700 nm

UV light spec

less than 400 nm

Infrared light spec

greater than 700 nm

Light spec order from shortest to longest wavelenth

Gamma, Xray, UV, visible, infrared, radar, FM radio, TV, AM radio, AC circuits

Range of wavelength peaks in retina

420 nm for violet --> S cones

530 nm for green --> M cones

560 nm for yellow-green --> L cones

496 nm --> rods

Light's effect on retina

1) Under normal, no light condition, Na+ channels on photoreceptors are held open by cGMP.

2) Shine light, changing shape of retinal

3) rhodopsin dissociates into retinal and opsin -

4) opsin combines with and activates a g-protein called transducin (about 500 of these activated per rhodopsin)

4) Transducin activates phosphodiesterase

5) PDE converts cGMP to 5'-GMP (about 2000 cGMP per PDE

6) reduced cGMP causes Na+ channels to close

7) cell hyperpolarizes

In photoreceptors the brighter the light, the _______ the hyperpolarization

the greater

Photoreceptor layout

There is an inner segment and outer segment.

Outer segment = contains many discs, each containing many rhodopsin proteins

Inner segment = where hyperpolarity is measure, area where light passes first before reaching outer segement

Hyperpolarizing photoreceptors decreases________ release

glutamate. What effect this has depends on the bipolar cell/type of glutamate receptor maybe

Bipolar will be inhibited by light if it is ________

off-center/on-surround, where light in the center of the field inhibits the cells

Bipolar will be excited by light if it is ________

on-center/off-surround, where light in the center of the field excited the cells

Which cells in retina have receptive fields?

bipolar and ganglion

For on-center, If you illuminate the entire center...

you see a large depolariation in the bipolar cell

you see many AP in the ganglion cell

For on-center, If you illuminate the entire surround...

you see a large hyperpolarization in the bipolar cell

you see a drop/few AP in the ganglion cell

For on-center, If you illuminate the entire center and surround...

you see a small depolarization in bipolar cell

you see sporadic/normal AP in the ganglion cell

most axons from the optic nerve terminate on the....

lateral geniculate nucleus AKA visual thalamus

Pathway of visual processing

retina --> LGN --> Occipital cortex/visual cortex/prmary visual cortex/V1/striate cortex

Optic radiation

projections from the LGN to the PVC

extrastriate cortex

surrounding cortical regions are also critical for vision

Lateral geniculate nucleus

Cells here respond like retina, can also be activated by light

6 layers:

Magnocellular - 2 inner layers that contain larger cells, not for color vision

Parvocellular - 4 outer layers that contain smaller cells, for color vision

LGN cells have concentric fields (like retina)

Cells in the visual cortex respond to...

more complicated stimuli, like things moving in a certain direction

Magnocellular cells

Have relatively large receptive fields, 2 inner most layers, larger cells,

Input to here is from large ganglion M-cells

Do not respond to color


Have relatively large receptive fields, 4 outer most layers, smaller cells,

Input to here is from small ganglion P-cells, that get input from cones

Do respond to color

Primary Visual cortex/visual cortex/occipital cortex/V1

Not very sensitive to light, need more specific stimuli

About 50% of V1 is dedicated to the fovea