Vision Flashcards

(59 cards)

1
Q

What happens when light strikes a perpendicular surface?

A

-continues through surface without bending

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2
Q

What does the degree of refraction depend on?

A
  • ratio of two refractive indices of the two transparent media
  • degree of angulation between the interface and the entering wave front of the light waves
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3
Q

What is refractive index?

A

-the ration of the velocity of light in air to the velocity of light traveling in the substance

RI air: 1.00

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4
Q

What is refractive power?

A

-a measure of how much a lens bends light waves. Measured in diopters.

1 diopter = 1 m/ focal length

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5
Q

What is the focal point?

A

-the point through which all parallel rays of light will pass after passing through each part

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6
Q

What is focal length?

A

-the distance from the center of the lens to the focal

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7
Q

Convex vs concave lens

A
  • convex -> converging lens

- concave -> diverging lens

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8
Q

How will the object projected on the retina be changed from the actual image?

A

-reversed and inverted

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9
Q

Define emmetropia.

A

-state of vision where an object at infinity is in sharp focus with the eye lens in a neutral or relaxed state

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10
Q

Differentiate between hyperopia vs myopia.

A

Hyperopia: farsightedness, positive lens, diverging lens

Myopia: nearsidedness, negative lens, converging lens, light rays in front of retina

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11
Q

What is visual acuity? What is the max visual acuity?

A
  • a measure of the resolving power of the eye

- max visual acuity for two point light source is 1.5-2mm

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12
Q

What forms aqueous humor?

A

-ciliary processes

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13
Q

How is aqueous humor formed?

A
  • ciliary apparatus consists of two opposing layers of epithelial cells with a space between them
  • Na+ are actively transported into this space and are accompanied by Cl- and CO3-
  • the ions draw water into the space and the aqueous solution is then passed into the anterior chamber
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14
Q

How does fluid flow in the eye?

A

-flows from anterior chamber into the canal of Schlemm and from there into aqueous veins in the sclera

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15
Q

How measures intraocular pressure? What is normal pressure?

A
  • a tonometer

- 15mm Hg is normal pressure

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16
Q

What is glaucoma?

A

-damage to the optic nerve caused by a buildup of pressure

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17
Q

What are the photosensitive pigments in rods and cones?

A
  • transmembrane conjugated proteins
  • rods -> rhodopsin
  • cones -> 3 color pigments
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18
Q

What are the major functional segments of the rods and cones?

A
  • outer segment: site of light-sensitive photo chemicals
  • inner segment: contains organelles, esp mitochindria
  • nucleus
  • synaptic body: connects with horizontal and bipolar cells
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19
Q

What is rhodopsin-retinal visual cycle?

A
  • rhodopsin = scotopsin + 11-cis retinal
  • rhodopsin + light -> scotopsin + all-trans retinal
  • metarhodopsin II is an intermediate in this pathway that excites electrical changes in the rods
  • all-trans retinal -> 11-cis retinal (requires isomerase and metabolic energy)
  • 11-cis retinal recombines with scotopsin -> rhodopsin

2 pathways:

  • all-trans retinal -> all-trans retinol (vitamin A)
  • all-trans retinol -> 11-cis retinol -> 11-cis retinal
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20
Q

Compare the ion flow in the dark vs light.

A
  • excitation of the rod causes increased negativity of the intrarod membrane potential (hyperpolarization)
  • decomposition of rhodopsin decreases rod membrane conductance for Na+ in the outer segment
  • results in hyperpolarization of entire rod membrane
  • inner segment continually pumps Na+ from inside rod to the outside and K- in opposite directions
  • K- leak out of cell via non-gated channels
  • negative potential is created on the inside of the cell
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21
Q

Outer segment of rods in the dark vs light.

A

Dark:

  • membrane is leaky to Na that flow through cGMP-gated channels
  • Na leak into cell and neutralize much of the negativity on the inside of the entire cell
  • under dark conditions there is reduced electronegativity inside the membrane

Light:

  • rhodopsin begins to decompose
  • retinal portion is activated and stimulates transducin
  • transducin activates cGMP phosphodiesterase
  • cGMP phosphodiesterase catalyzes cGMP -> 5’GMP
  • reduction in cGMP causes closure of Na channels
  • photoreceptor then becomes hyperpolarizes
  • rhodopsin channels close
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22
Q

What is refraction?

A

-the bending of light waves at an angulated surface of a transparent material

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23
Q

What are the layers of the retina?

A
  • photoreceptors
  • horizontal cells
  • bipolar cells
  • amacrine cells
  • ganglion cells
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24
Q

Describe the photoreceptors.

A
  • rods and cones
  • transmit signals to outer plexiform layer (layer of synaptic connections)
  • synapse with bipolar cells and horizontal cells
25
Describe horizontal cells.
- transmit signals from rods and cones to bipolar cells - transmit signals to outer plexiform layer - output is always inhibitory (lateral inhibition)
26
Describe bipolar cells.
- transmit signals from rods, cones, and horizontal cells - transmit signals to inner plexiform layer - synapse with amacrine and ganglion cells
27
Describe amacrine cells.
-transmit signals +directly from bipolar to ganglion cells +within inner plexiform layer from axons of bipolar cells to dendrites of ganglion cells or to other amacrine cells
28
Describe ganglion cells.
- transmit signals from retina to brain - axons make up optic nerves - ONLY retina cells that transmit AP (others use electrotonic conduction)
29
What is the only cell that transmits AP?
-ganglion cells
30
Describe interplexiform cells.
- transmit from inner plexiform later to outer plexiform layer (retrograde) - inhibitory signals (lateral inhibition)
31
What type of vision does the fovea region specialize in?
-cone vision
32
What three neurons are involved in the direct foveal pathway?
- cones - bipolar cells - ganglion cells
33
What four neurons are involved in rod vision?
- rods - bipolar cells - amacrine cells - ganglion cells
34
What neurotransmitter do rods and cones send to bipolar cells?
-Glu
35
What neurotransmitters do amacrine cells transmit?
-GABA, glycine, dopamine, ACh, indolamine (all inhibitory)
36
How many amacrine cells are there and what functions do they serve?
-30 kinds - direct pathway from rod conduction - responds to onset of continuing vision but fades rapidly - respond at the offset of visual signals, response fades rapidly - respond when light is turned on/off - responds to movement of a spot across the retina in a specific direction - INTERNEURONS that help analyze visual signals before they leave the retina
37
What are the 3 types of ganglion cells?
-W, X, Y
38
How many rods and cones converge on a ganglion cell?
- 60 rods | - 2 cones
39
What happens to rods and cones as they approach the fovea?
-they become more slender +increases visual acuity +in central fovea there are only slender cones
40
What are W ganglion cells?
- compose 40% of ganglion cells - small - transmit signals at 8m/sec - receive most of their excitation from rods through bipolar and amacrine cells - have broad fields in the peripheral retina because their dendrites spread widely in the inner plexiform layer
41
What are X ganglion cells?
- 55% - medium - 14m/sec - small fields (discrete retinal locations) - receives input from at least one cone cell -> responsible for all color vision
42
What are Y ganglion cells?
- 5% - large - 50m/sec - respond to rapid changes in visual image - apprise the CNS when a new visual event occurs anywhere in the field w/o great accuracy with respect to location of field
43
What is the dorsal lateral geniculate nucleus responsible for?
- receive input from optic nerve - relays information from optic tract to visual cortex by way of optic radiation - 50% decussate on in optic chasm
44
What are the 6 nuclear layers in the lateral genicular even nucleus?
- II, III, V receive signals from lateral half of ipsilateral retina - I, IV, VI receive signals from medial half of opposite retina
45
What are layers I and II in the genicular nucleus responsible for?
- magnocellular layers - contain large neurons - receive input almost entirely from large Y ganglion cells - provides rapidly conducting pathway to visual cortex - transmits ONLY black and white - point to point transmission is poor
46
What are layers III and VI responsible for in the genicular nucleus?
- parvocellular layers - small-medium neurons - primarily X ganglion - moderate conducting pathway to visual cortex - transmits color - accurate point to point transmission
47
What is transmission gating?
-genicular even nucleus controls how much of the single is allows to pass to the cortex
48
What are the sources of transmission gating?
- corticofugal fibers from primary visual cortex - reticular areas of the mesencephalon -both of these sources are inhibitory and help highlight visual info that is allowed to pass
49
What is the primary visual cortex?
- striate cortex -> occipital cortex - signals from macular area terminate near the occipital pole - signals from the more peripheral retina terminate at or in concentric half circles anterior to the pole but still along the cal carmine fissure - 6 distinct layers
50
Geniculocalcarine fibers terminate mainly in layer _______.
IV
51
What are the subdivisions of layer IV?
- Y ganglion cells terminate in layer IVca | - X ganglion cells terminate in layer IVcB and IVa
52
The visual cortex is organized into several million vertical columns of neurons. How many neurons per column?
1000
53
What do color blobs in the columns of secondary visual areas do?
-receive lateral signals from adjacent visual columns and are activated specifically by color signals
54
Signals from the two separate eyes enter ____________ stripes of columns in layer IV.
Alternating
55
Cortical area deciphers whether the. Retrospective areas of the two visual images from the two separate eyes are in register with each other.
- deciphered info is used to adjust the directional gaze of the eyes - required for steropsis
56
Accommodation in children.
-refractive power of the lens can voluntarily increase from 20 to 34 diopters (accommodation of 14 diopters)
57
Accommodation in a young person.
-when lens is relaxed it is almost spherical -suspensory ligaments attached radially around the lens create a tension that causes the lens to remain relatively flat under normal eye conditions +meridian all fibers of ciliary muscle contract and release tension on lens +circular fibers of ciliary muscle also decrease tension on lens
58
Which cranial nerve controls both sets of ciliary muscles?
3, oculomotor
59
Accommodation in an older person.
- lens becomes larger and thicker with age - lens becomes less elastic - power of accommodation decreases to less than 2 diopters by the age of 45-50 - decrease to 0 by the age of 70 - presbyopia