Lecture 7: vision I Flashcards Preview

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Flashcards in Lecture 7: vision I Deck (86)
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1
Q

Refraction?

A

bending of light waves at an angulated surface of transient material

2
Q

What can alter the degree of refraction?

A
  • ratio of two reflective indices

- degree of angle between interface and entering wave light

3
Q

What is refractive index?

A
  • ratio of velocity of light in air: velocity of light traveling in substance
4
Q

What is refractive Power?

A
  • measure of how much a lens bends light waves. measure in diopters
5
Q

What is focal Point?

A
  • point where all parallel rays converge after passing through the lens
6
Q

What is focal length?

A
  • distance from center of lens to the focal point
7
Q

Describe how the depth of focus of the lens changes?

A

The depth of focus is inversely related to the size of the pupil diameter

8
Q

What is Emmetropia?

A
  • eye has normal depth of focus

- when ciliary muscles relax distant object light rays sharply focus on the retina

9
Q

What is hyperopia?

A
  • farsightedness
  • distant objects seen clearly
  • caused by eyeball that is too short
10
Q

What is Myopia?

A
  • nearsightedness
11
Q

What causes light rays to converge in from of the retina?

A
  • myopia

- caused by eyeball that is too long

12
Q

What is the maximum visual acuity for two-point sources?

A

1.5 to 2 mm

13
Q

What is visual acuity?

A

measures the resolving power of eye

- eye chart test

14
Q

Where does the aqueous humor come from?

A

ciliary processes

15
Q

In order to pull the aqueous humor into the anterior chamber, what is the environment like?

A

it would be high osmolarity. High concentration of ions to draw fluid through via osmosis

16
Q

What is glaucoma?

A

Increased intraocular pressure that will lead to damage of the optic nerve and potentially vision loss, if not corrected

17
Q

What is the photosenstivie pigment of rods?

A

rhodopsin

18
Q

What is the photosensitive pigment in cones?

A

contain three different pigments

19
Q

What two components join together to form rhodopsin?

A

scotopsin and 11-cis retinal

20
Q

What happens when rhodopsin is exposed to light waves?

A

the cis is converted to trans and does not have the proper orientation to bind with scotopsin
- forms bathorhodopsin

21
Q

What is activated rhodopsin and what does it do?

A
  • metarhodopsin II

- excites electrical charges in rods that signal to optic nerve potential

22
Q

Degradation of metarhodopsin II produces what compounds?

A
  • all trans retinal and scotopsin

- isomerize with isomerase to the cis form

23
Q

How can increased levels of Vitamin A be helpful with vision?

A

Vitamin A is isomerized to 11-cis retinol and converted to 11-cis retinal

24
Q

What is the resulting receptor potential when the rods are exposed to light?

A

increasing negativity. hyperpolarizing

25
Q

Why does activation of rhodopsin cause hyperpolarization?

A
  • the decompensation of rhodopsin decreases the rod membrane conductance for Na ions, in the outer segment of the rod.
  • and the rod is continually pumping Na ions out of the membrane
26
Q

Explain how a -40 mV potential is generated in the rod in a normal dark condition?

A
  • cGMP gated channels are open and allow leaking of Na ions back inside the rod membrane
27
Q

In what conditions are you likely to find a hyperpolarized rod, and a less polarized rod?

A
  • hyperpolarized: in light conditions

- non polarized: in dark conditions

28
Q

What is light adaptation?

A
  • results in the reduction of rhodopsin and photosensitive chemicals
  • reduces the sensitivity of the eye to light
29
Q

What is dark adaptation?

A
  • results in low light and the accumulation of rhodopsin and other light sensitive pigments
  • increases the sensitivity of the eye to light
30
Q

How do we perceive color?

A
  • based on the mixing ratio of blue, green , red stimulation of the cones
31
Q

Green and red cones are required to see what colors?

A
  • green
  • yellow
  • orange
  • red
32
Q

Blue, green and red cones are required to see what colors?

A
  • violet
  • blue
  • green
33
Q

What is protanope?

A

loss of red cones

34
Q

What is deuteranope?

A
  • loss of green cones
35
Q

What is loss of blue cones?

A
  • blue weakness
36
Q

What are the different neuronal cell types of the retina from superficial to deep?

A
  • rods and cones
  • horizontal cells
  • bipolar cells
  • amacrine cells
  • ganglion cells
37
Q

Where do rods and cones synapse?

A
  • bipolar and horizontal cells
38
Q

What is the function of horizontal cells?

A
  • transmit signal from outer plexiform layer to horizontally from rods and cones to the bipolar cells
39
Q

What is the function of bipolar cells?

A
  • transmit signal from rods, cones, horizontal cells to inner plexiform layer
  • synapse with ganglion and amacrine cells
40
Q

What is the function of amacrine cells?

A
  • transmit signal from bipolar to ganglion cells

- send signal across inner plexiform layer

41
Q

What is the function of the ganglion cells?

A
  • transmit signal from retina to the optic nerve
42
Q

What is the interplexiform cell?

A
  • transmits retrograde signal from inner to outer plexiform layer
  • inhibitory and control lateral spread of vision
43
Q

What neurons are in the foveal region direct pathway (aka: fast cone system)?

A
  • cones
  • bipolar cells
  • ganglion cells
44
Q

What four neurons purely make up rod vision?

A
  • rods
  • bipolar cells
  • amacrine cells
  • ganglion cells
45
Q

What neurotransmitter is released at the synapse of rods/cones and bipolar cells?

A

glutatmate

46
Q

Amacrine cells secrete what neurotransmitters that are all inhibitory?

A
  • GABA
  • glycine
  • dopamine
  • acetylcholine
  • indolamine
47
Q

Which neurons are the only ones that will transmit their visual signals as an action potential?

A
  • ganglion cells
48
Q

What is the importance of electrotonic conduction within the eyes?

A
  • this process allows for rods and cones to respond to varying levels of lighting
  • eliminates the all or none action potential
49
Q

With the diverse amount of amacrine cells, what if the most likely function common to them?

A
  • interneurons that analyze visual signals before they leave the retina
50
Q

If an amacrine cell is directionally sensitive, what does that mean?

A
  • responds to movement of a spot across the retina
51
Q

What is the effect of fewer rods and cones converging on an optic nerve at the fovea?

A
  • increased visual acuity

- the central fovea only contains slender cones (increases visual acuity)

52
Q

The absence of rods at the central fovea reduces what aspect of sight, at this area?

A
  • sensitivity to weak light.
53
Q

Why is the peripheral retina more sensitive to weak light?

A
  • multiple rods converge on an optic nerve
54
Q

Which type of retinal ganglion cells are important for crude rod vision in dark conditions?

A
  • type W
55
Q

What types of signals are sent from the type W ganglion cells?

A
  • slow velocity
  • excitation from rods
  • transmit by bipolar and amacrine cells
56
Q

Color vision most likely comes from what retinal ganglion cells?

A
  • X
57
Q

What type of signals can be represented by type X ganglion cells?

A
  • fine detailed images on discrete retinal locations

- due to fact that cells receive input from one or more cones

58
Q

What is characteristic about the Y ganglion cells?

A
  • responds to rapid changes in vision

- most likely to apprise the CNS of new visual activity with low accuracy

59
Q

What portions of the optic nerves cross at the optic chiasm?

A

nasal halves of the retina

60
Q

What visual fields compose the left optic tract and where does it synapse at?

A
  • the left lateral field and right nasal field

- synapse in the dorsal lateral geniculate nucleus in the thalamus

61
Q

What visual fields compose the right optic tract and where will it synapse?

A
  • the right lateral field and the left nasal field

- synapse in the dorsal lateral geniculate nucleus of the thalamus

62
Q

From the dorsal lateral geniculate nucleus where do optic fibers pass to provide vision?

A
  • geniculocalacrine fibers move too the primary visual cortex via optic radiation
63
Q

Where is the primary visual cortex located?

A
  • the calcarine fissure of the medial occipital lobe
64
Q

What are the two primary functions of the dorsal lateral geniculate nucleus?

A
  • relay visual information from optic tract to visual cortex via optic radiation
  • regulates amount of signals that pass to the cortex.
65
Q

The dorsal lateral geniculate nucleus receives signals from the lateral half of the ipsilateral retina on what layers?

A
  • layers II, III, V
66
Q

What visual fields do layers I, IV, and VI of the dorsal lateral geniculate nucleus receive?

A
  • medial field of the contralateral eye
67
Q

What fields of view do layers II, III, V of the DLGN receive?

A
  • lateral ipsilateral views
68
Q

What is contained in layers I and II of the DLGN?

A
  • magnocellular layers
  • input from Y ganglion cells
  • rapid conduction of visual cortex
  • black and white only; poor point to point transmission
69
Q

What are layers III and IV of the DLGN, and what do they respond to?

A
  • parvocellular layers
  • input from X ganglion
  • transmit color
  • accurate point to point transmission
70
Q

What is the source of DLGN transmission gating?

A
  • corticofugal fibers from primary visual cortex
  • reticular area of mesencephalon
  • both are inhibitory and highlight visual information that is allowed to pass
71
Q

The primary cortex contains an region where the macular area of sight terminates. Where is that?

A
  • near the occipital pole
72
Q

Where do signals from the peripheral retina terminate?

A
  • concentric half anterior to pole, still within the calcarine fissure
73
Q

Where do geniculocalcarine fibers terminate in the primary visual cortex?

A
  • layer IV
74
Q

Type Y ganglion fibers terminate in what layer of the primary visual cortex?

A
  • layer IVc alpha
75
Q

Type X ganglion fibers terminate in what layer of the primary visual cortex?

A
  • layer IVc beta and IVa
76
Q

After passing into the primary cortex where do signals next encounter?

A
  • brodmanns’ area 18

- here the signals are analyzed for visual meaning

77
Q

In layer IV of the cortical area, images are analyzed to help adjust what?

A
  • directional gaze of each eye

- used in stereopsis

78
Q

“Complex cells” are able to detect what?

A
  • detect line orientation when a line is displaced laterally or vertically in the visual field
79
Q

“Simple” cells are able to detect what and are located where?

A
  • able to detect orientation of lines, and different orientations stimulate different sets of cells
  • these cells are found in the layer IV of primary visual cortex
80
Q

What is the autonomic nerve pathway of the eye starting with the synapse from the pretectal region?

A
  • preganglionic fibers arise in the Edinger-Westphal nucleus and pass with CN III to synapse in ciliary ganglion
  • ciliary ganglion synapse converts to postganlgionic parasympathetic fibers that move through ciliary nerves to the eyeball
81
Q

What are the actions of the ciliary postganglionic ciliary nerves of the eye?

A
  • excite the ciliary muscle to control accommodation

- control the sphincter that constricts the pupil

82
Q

When the lens in spherical what are the ciliary muscles doing?

A
  • contracted

- long distance objects

83
Q

When the ciliary muscles contract, what type of shape does the lens take on?

A
  • spherical

- objects at short distance

84
Q

What two fibers are under control of ciliary nerves (CN III)?

A
  • meridional fibers that contract and release lens tension, forming a sphere
  • circular fibers that also decrease lens tension
85
Q

What is presbyopia and when does it occur?

A
  • loss of the ability to accommodate
  • occurs by 45-70 y/o
  • due to lens thickening and becoming larger
86
Q

What is the effect of the larger and thicker lens in elderly individuals

A
  • presbyopia

- loss of accommodation to significant degree