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Neuro Test 3 > physiology of the visual field > Flashcards

physiology of the visual field Flashcards

1
Q

refraction

A

the fact or phenomenon of light, radio waves, etc being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density

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2
Q

first sight of refraction

A

cornea

  • not variable
  • 2/3 of light bending
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3
Q

second sight of refraction

A

lens

  • variable
  • depends on curvature of lens under physiologic control
  • rounder = more refraction
  • flatter = less refraction
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4
Q

what is required to change the curvature of the lens?

A
  • ciliary muscle
  • suspensory ligaments
  • normal lens
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5
Q

increase curvature of lens

A
  • ciliary m contracts
  • allows suspensory ligaments to loosen
  • lens more rounded shape by natural recoil
  • near vision
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6
Q

decrease curvature

A
  • ciliary m relaxes
  • suspensory ligaments tighten
  • lens pulled tight flattening it
  • used for far vision
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7
Q

presbyopia

A

lens becomes stiffer in aging, loss of elasticity

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8
Q

near response

A
  1. contraction of ciliary ms
  2. convergence of eyes to the point of focus
  3. constriction of pupil
    - reduces opening for light to enter
    - eliminates diverging light rays
    - allows better focus
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9
Q

path of light from when it enters at cornea to activating photoreceptor

A

cornea, lens, hummor, vitreous, GCL, IP, INL, OPL, ONL

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10
Q

5 neuron types in the retina

A

vertically oriented

  1. receptor cells (rod and cone)
  2. bipolar cells
  3. ganglion cells - MG cells

horizontally oriented

  1. horizontal cells
  2. amacrine cells
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11
Q

photoreceptors

A

rods and cones

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12
Q

rod system

A
  • convergence: many rods + many bipolars –> 1 ganglion cell
  • allows to see in dim light
  • sacrifices acuity to gain sensitivity
  • off center
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13
Q

cone system

A
  • less convergence: 1 receptor –> 1 bipolar cell –> 1 ganglion cell
  • maximizes acuity
  • bright light
  • center
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14
Q

what do rods and cones constantly release?

A

glutamate

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15
Q

when is glutamate release highest?

A

dark

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16
Q

when is glutamate release lowest?

A

light

-stimulation by photons –> hyperpolarize –> less glutamate release

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17
Q

activation of bipolar cell by cone

A

1 photon stimulates photoreceptor
2 photoreceptor hyperpolarizes
3 glutamate release onto the bipolar cell DECREASES

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18
Q

ON center

A

CENTER: causes depolarization
PERIPHERY: causes hyperpolarization
increase discharge rate to luminance increments in the receptive field center

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19
Q

OFF center

A

CENTER: hyperpolarizes
PERIPHERY: depolarizes
increase discharge rate to luminance decrements in the receptive field center

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20
Q

ON center bipolar cell in darkness

A
  1. glutamate would activate Gi GPCR metabotropic receptor on the ON-center bipolar cell
  2. results in a decrease in cation influx into the bipolar cell
  3. hyperpolaries cell
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21
Q

ON center bipolar cell in brightness

A
  1. light photons decrease the presence of glutamate
  2. less glutamate around
  3. less activation of metabotropic receptor on the ON center bipolar cell
  4. less Gi signaling
  5. results in an INCREASE in cation influx into the bipolar ell
  6. depolarizes the cell
22
Q

OFF center bipolar cell in darkness

A
  1. glutamate would activate AMPA receptor on the OFF center bipolar cell
  2. results in an increase in cation influx into the bipolar cell
  3. depolarizes cell
23
Q

OFF center bipolar cell in brightness

A
  1. light photons decrease presence of glutamate
  2. less glutamate around
  3. less activation of AMPA receptor on the OFF center bipolar cell
  4. results in decrease in cation influx into the bipolar cell
  5. hyperpolarizes the cell
24
Q

Do ganglion cells have ON center and OFF center varieties?

A

yes –> activated/deactivated by glutamate released when bipolar cells depolarize

  • ganglion cell axons become fibers of optic nerve
  • in cortex, ganglion cells will release glutamate
25
Q

activation of bipolar cell by rod photoreceptors

A
  1. many rods converge on one ON center bipolar cell
  2. connects to a “rod-bipolar cell” and “rod amacrine cell” which both function as interneurons inhibiting the cones with glycine or GABA
  3. connects to a “cone-bipolar cell”
  4. connects to ganglion cell
26
Q

direct targets of the retina

A
  • LGB
  • superior colliculus
  • pretectum
  • hypothalamus
  • accessory optic nuclei
27
Q

LGB functions

A
  1. control the motions of the eyes to converge on a point of interest
  2. control the focus of the eyes based on distance
  3. determine relative position of objects to map them in space
  4. detect movement relative to an object
28
Q

optic radiations

A

axons of LGB relay cells to visual cortex on same side

-maintains retinotopic organization

29
Q

anatomical areas of visual processing

A

17 primary visual cortex
18 parastriate cortex
19 peristriate cortex

30
Q

functional areas of visual processing

A 
V1 primary visual cortex (17)
V2 greater part of 18
V3 narrow strip of 18
V4 area 19
V5 middle temporal (MT) area of 19
31
Q

primary visual cortex layers

A

I, II, III - networking with IV
IV receives input from LGB
V and VI main output layers: LGB, thalamus, subcortical regions

32
Q

What layers of the cortex do columns span?

A

all 6 layers

33
Q

ocular dominance columns

A

a slab of cells that preferentially respond to input from one eye or the other

34
Q

orientation columns

A

organized region of neurons that are excited by visual line stimuli of varying angles spanning 6 layers of cortex oriented perpendicular to cortical surface

35
Q

blobs in primary visual corex

A

collections of 6 layers of the cortex organized region of neurons that are sensitive to color assemble into cylindrical shapes.
-3 color coding cones required for color detection

36
Q

S-cone

A

blue 437 nm

37
Q

rod

A

498 nm

38
Q

M-cone

A

green 533 nm

39
Q

L-cone

A

red 564 nm

40
Q

stripes

A

ocular dominance

41
Q

swirls

A

orientation columns

42
Q

cytochrome oxidase stain

A

blobs

43
Q

V1 major job

A

edges and contours of objects

44
Q

V2 major job

A

depth

45
Q

V3 major job

A

ID of motion

46
Q

V4 major job

A

color processing

47
Q

dorsal pathway

A

from primary visual cortex and goes tot the parietal/frontal cortex

  • primary path associating vision with movement
  • completes motor acts based on visual input
  • passes through V3
48
Q

ventral pathway

A

from primary visual cortex to the inferior temporal cortex

  • primarily involved in interpreting images (recognizing or copying shapes, forms, faces) and complex patterns
  • copying/naming objects are separate functions in temporal lobe. damage to one area is possible without damaging the other
  • facial recognition is a specialized area
49
Q

what are MG cells?

A

a subset of ganglion cells detects light directly via the blue-sensitive photopigment melanopsin

50
Q

What does melanopsin do?

A

light, via melanopsin causes changes in calcium levels in MG cells
-non-image-forming light -responsive system –> project to hypothalamus (suprachiasmatic nucleus) (circaidian rhythms)

Neuro Test 3 (11 decks)

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