Visual System (3)

Question 1

what is light energy

Answer 1

electromagnetic radiation

Question 2

what are the 3 perceived characteristics of light

Answer 2

hue: spectrum/wavelength of light (color)
brightness: height of the wavelength (amplitude)
saturation: purity of the wavelength

Question 3

what are the structural characteristics of the eye

Answer 3

pupil: opening where light enters the eye
sclera: white of the eye (absorbs/reflects light)
iris: color of the eyes
cornea: transparent external surface (focuses light on back of retina)
optic nerve: bindle of axons from retina

Question 4

what are three abnormalities of vision and what are they cause by

Answer 4

myopia/nearsightedness: eyeball too long
hyperopia/farsightedness: eyeball too short
astigmatism: uneven cornea/lens

Question 5

what is the visual field of vision

Answer 5

the receptive field: the area of the retina that, when stimulated with light, changes a cell’s membrane potential

Question 6

what is the difference between m-type and p-type cells

Answer 6

m-type: movement

p-type: static characteristics (ex. color)

Question 7

how is the retina organized (pathway of light to photoreceptors)

Answer 7

light passes through the ganglion, bipolar, amacrine, and horizontal cells before reaching the photoreceptors

Question 8

what are the different cell layers from first in the path of light to the last in the path of light

Answer 8

ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, layer of photoreceptor outer segments, pigmented epithelium

Question 9

what is the mechanism of electromagnetic energy transduction into photoreceptors

Answer 9

in both rods and cones: light stimulus activates the inhibitory g-protein which breaks down cGMP and HYPERPOLARIZES the cell (influx of K) leading to less neurotransmitter release

dark current: in the dark, the photoreceptors will be depolarized leading to more neurotransmitter release

in cones: red=higher wavelength, lower frequency; blue=lower wavelength, higher frequency

Question 10

what are the properties of central and peripheral vision

Answer 10

central vision: more cones (details and color) on fovea

peripheral vision: more rods (shape)

Question 11

describe what happens in response to LIGHT stimulus in the CENTER

Answer 11

1. the photoreceptor hyperpolarizes in response to light -> releases less glutamate
2. on center bipolar cells would depolarize because of less glutamate in the metabotropic (inhibitory) receptors
3. leads to more neurotransmitter release

Question 12

describe what happens to LIGHT stimulus on the SURROUND

Answer 12

1. the photoreceptors would hyperpolarize in response to light, releasing less glutamate
2. since surround, the horizontal cell would act the same as the photoreceptor and hyperpolarize so no glycine would be released
3. because no glycine is released, there is more glutamate released
4. the off center bipolar cell will depolarize in response to more glutamate because it is an ionotropic (excitatory) receptor
5. the cell depolarizing will allow for more neurotransmitter release

Question 13

describe what happens to DARK stimulus in the CENTER

Answer 13

1, the photoreceptors will depolarize in response to darkness

2. because depolarized, there will be more glutamate released
3. because more glutamate is released, the on center cell will be hyperpolarized because there is more inhibitory glutamate for the metabotropic receptor
4. because the metabotropic receptors have more inhibitory glutamate, there will be less neurotransmitter release

Question 14

describe what happens to DARK stimulus in the SURROUND

Answer 14

1. the photoreceptors are depolarized in response to darkness so more glutamate is released
2. since in surround, horizontal cells act like the photoreceptors and depolarize
3. lots of glycine is released which inhibits further glutamate release
4. because there is less glutamate released, the off center bipolar cell will hyperpolarize
5. since the bipolar cell hyperpolarizes, the ionotropic receptors do not have as much glutamate so there will be less neurotransmitter release

Question 15

what are the receptive fields obtained for ganglion cells

Answer 15

surround ganglion cells hyperpolarize in response to dark and depolarize in response to light
center ganglion cells will depolarize in response to dark and hyperpolarize in response to light

Question 16

what is the difference between m-type and p-type ganglion cells

Answer 16

m-type: larger receptive fields, larger dendritic field, more responsive to movement (dorsal)
p-type: smaller cell body, smaller dendritic tree, more sustained AP, driven by static characteristics

Question 17

describe the trichromatic and color opponent mechanisms of color vision

Answer 17

trichromatic: three different opsins (red, blue, green) and contributions of each of these cones to the retinal signal make up color
color opponents: red/green, blue/yellow, black/white (ex. red will depolarize the cell while green will hyperpolarize the cell)

Question 18

describe the visual pathway!!

Answer 18

1. photoreceptors
2. if stimulus on surround, horizontal cells
3. ganglion cells (can send AP)
4. optic nerve (CNS)
5. optic chiasm (pathways cross)
6. optic tract
7. lateral geniculate nucleus (thalamus)
8. optic radiation (connects LGN to visual cortex)
9. primary visual cortex/occipital lobe

Question 19

how does information from the left visual field end up on the right side of the brain

Answer 19

information from the NASAL side of the left eye will cross to the right optic tract
information from the NASAL side of the right eye will cross to the left optic tract

Question 20

how is the LGN organized

Answer 20

six layer organization
layers 1-2: receive information from different eyes, ventral, m-type ganglion cells, cell bodies are larger
layers 3-6: p-type ganglion cells, dorsal
*each layer only receives information from one eye

Question 21

how is the striate (primary visual) cortex organized

Answer 21

six layer organization
layer 1: most near pia mater, contains few cells, recipient of LGN axon terminals
layer 4: recipient of major LGN inputs
layer: 5/6: deepest layer, associated with output

Question 22

how and where is binocular vision observed in the primary visual cortex

Answer 22

through the lateral geniculate nucleus (thalamus) and neurons in the LGN will send axons to the primary visual cortex

Question 23

which cortical cells are orientation selective and which are direction selective

Answer 23

orientation selective: simple cortical cells

direction selective: complex cortical cells

Question 24

describe the different cortical modules (simple and complex cortical cells)

Answer 24

simple cortical cells: looking at shape and color of objects, recognizing objects, ventral stream, layers 2 and 3
complex cortical cells: movements, dorsal stream

Question 25

what is the difference between the dorsal and ventral streams of the visual system

Answer 25

dorsal stream: movement and analysis of movement (parietal lobe)
ventral stream: perception of visual world and recognition of objects (temporal gyrus)