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Neuro 2nd Half > visual physiology > Flashcards

visual physiology Flashcards

1
Q

what change light into electrical potentials? two types?

A

photoreceptors; rods and cones

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2
Q

where in the eye are photoreceptors located?

A

outermost layer of the neural retina

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3
Q

rods

A

detect low light (good light sensitivity) but bad visual acuity
no color discrimination

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4
Q

cones

A

good visual acuity and color vision, but bad sensitivity to light

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5
Q

ANATOMY: Both rods and cones have…

A

outer segment with stack of either membranous discs (rods) or infoldings (cones) which contain the photopigments that respond to light

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6
Q

discs in outer segment?

infoldings in outer segment?

A

rods

cones

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7
Q 
Rods vs Cones
which has more per retina?
photopigment?
distribution?
color discrimination?
acuity?
wiring to ganglion cells?
temporal resolution?
light sensitivity?
A

rods –>almost 20x more
rods: rhodopsin, peripheral to fovea, no color discrimination, low acuity, highly convergent, poor resolution, high sensitivity

cones: 3 types of cone opsins, concentrated central in fovea, yes color discrimination, high acuity, less convergent, good resolution, low sensitivity to light

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8
Q

vision at…
low levels of illumination?
intermediate levels?
high levels?

A

scotopic vision
mesopic vision
photopic vision

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9
Q

scotopic vision

A

at low levels of light, rods only function

visual acuity is poor and no color perception

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10
Q

mesopic vision

A

middle levels of light, vision uses both rod and cone systems
improved acuity and poor color perception

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11
Q

photopic vision

A

high levels of light, vision is mostly just cone system
rod system is saturated and cant respond after that point
BEST visual acuity and color perception

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12
Q

photopic vision

A

high levels of light, vision is mostly just cone system
rod system is saturated and cant respond after that point
BEST visual acuity and color perception

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13
Q

photoreceptors are unusual in that…

A

their stimulus, light, produces hyperpolarization

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14
Q

photoreceptor mechanism (in the dark)

A
  • cGMP gated Na channel is open and depolarizes receptor(rod or cone)
  • receptor releases NT on bipolar cell
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15
Q

photoeceptor mechanism (in light)

A
  • light causes cGMP Na channel to close
  • Na/K atpase and K current hyperpolarize the receptor
  • NT release is decreased
  • more light = more hyperpolarization = less NT
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16
Q

flow of info:
roads and cones make direct synaptic contact with?
and in turn those make direct synaptic contact with?

A

bipolar cells

ganglion cells

17
Q

bipolar cell –> ganglion cell is always _____?

A

excitatory

18
Q

bipolar cell –> ganglion cell is always _____?

A

excitatory

19
Q

multiple ___ can converge on a single bipolar cell; but only one/few ____ can converge on a single bipolar cell

A

rods

cones

20
Q

greater _____ in the rod system allows greater light sensitivity but less _____

A

convergence

visual acuity

21
Q

info pathway to brain

A

photoreceptors –> bipolar cells –> ganglion cells –> optic tract fibers synapse in the lateral geniculate body in the brain or the superior colliculus

22
Q

On-center response to light

A
  • light hyperpolarizes the photoreceptor
  • decreases inhibitory NT released onto bipolar cell
  • depolarization of the bipolar cell and increased excitatory NT released onto ganglion cell
  • excited ganglion cell causes increased action potential firing rate
23
Q

off-surround response to light

A
  • light hyperpolarizes the off-surround receptor which hyperpolarizes adjacent horizontal cell causing less inhibitory NT onto on-center cone
  • depolarization of the on-center receptor
  • more inhibitory NT onto bipolar cell
  • bipolar cell hyperpolarizes and releases less NT onto ganglion cell
  • hyperpolarization of ganglion cell –> decreased firing rate
24
Q

off-surround response to light

A
  • light hyperpolarizes the off-surround receptor which hyperpolarizes adjacent horizontal cell causing less inhibitory NT onto on-center cone
  • depolarization of the on-center receptor
  • more inhibitory NT onto bipolar cell
  • bipolar cell hyperpolarizes and releases less NT onto ganglion cell
  • hyperpolarization of ganglion cell –> decreased firing rate
25
Q

what is the function of the on-center/off-surround system?

when is it useful?

A

to sharpen boundaries between areas of light and dark by making the black adjacent to the border appear blacker, and white whiter

  • –enhances visual acuity
  • –ex: when reading b/w paper or reading in different light levels
26
Q

does lateral inhibition in the oncenter.off surround system emohasize difference in illumination or the absolute illumination level?

A

the difference between two areas!

27
Q

illuminate the on center?
off surround?
all in light? all in dark?

A

increeased ganglion firing
decreased ganglion firing
firing is the same – only changes in transition areas to recognize edges

28
Q

3 cone types?

A

blue green and red

29
Q

each type of cone on its own is________

A

color blind - cant tell difference between change in color or light intensity

30
Q

which cone is least sensitive to light?

A

blue

31
Q

which cone is intermediate in sensitivity?

A

green

32
Q

cone that is most sensitive to light?

A

red

33
Q

blue cone is most sensitive to___

A

wavelengths that allow us to see blue to violet end of spectrum

34
Q

red and green cones are found throughout ____

A

the fovea, including center where fine detail is best

35
Q

fine detail is best in the…

A

central fovea

36
Q

blue cones are found___

A

in the fovea but not in the central part so they do not help with fine detail

37
Q

central foveal vision is ____

A

dichromatic (red and green cones only)

38
Q

absence of blue cones in central fovea solves what problem

A

chromatic abberration — where a blurred image is made due to the fact that the lens refracts blue light more than red and green

39
Q

red-green color blindness

A

a single cone type is missing or non functional
cannot distinguish between red and green
–recessive, sex linked trait on x chromosome
more common in males

Neuro 2nd Half (8 decks)

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