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Physiology II Exam 1 > Vision > Flashcards

Vision Flashcards

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
Q

Describe horizontal cells.

A
  • transmit signals from rods and cones to bipolar cells
  • transmit signals to outer plexiform layer
  • output is always inhibitory (lateral inhibition)
26
Q

Describe bipolar cells.

A
  • transmit signals from rods, cones, and horizontal cells
  • transmit signals to inner plexiform layer
  • synapse with amacrine and ganglion cells
27
Q

Describe amacrine cells.

A

-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
Q

Describe ganglion cells.

A
  • transmit signals from retina to brain
  • axons make up optic nerves
  • ONLY retina cells that transmit AP (others use electrotonic conduction)
29
Q

What is the only cell that transmits AP?

A

-ganglion cells

30
Q

Describe interplexiform cells.

A
  • transmit from inner plexiform later to outer plexiform layer (retrograde)
  • inhibitory signals (lateral inhibition)
31
Q

What type of vision does the fovea region specialize in?

A

-cone vision

32
Q

What three neurons are involved in the direct foveal pathway?

A
  • cones
  • bipolar cells
  • ganglion cells
33
Q

What four neurons are involved in rod vision?

A
  • rods
  • bipolar cells
  • amacrine cells
  • ganglion cells
34
Q

What neurotransmitter do rods and cones send to bipolar cells?

A

-Glu

35
Q

What neurotransmitters do amacrine cells transmit?

A

-GABA, glycine, dopamine, ACh, indolamine (all inhibitory)

36
Q

How many amacrine cells are there and what functions do they serve?

A

-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
Q

What are the 3 types of ganglion cells?

A

-W, X, Y

38
Q

How many rods and cones converge on a ganglion cell?

A
  • 60 rods

- 2 cones

39
Q

What happens to rods and cones as they approach the fovea?

A

-they become more slender
+increases visual acuity
+in central fovea there are only slender cones

40
Q

What are W ganglion cells?

A
  • 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
Q

What are X ganglion cells?

A
  • 55%
  • medium
  • 14m/sec
  • small fields (discrete retinal locations)
  • receives input from at least one cone cell -> responsible for all color vision
42
Q

What are Y ganglion cells?

A
  • 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
Q

What is the dorsal lateral geniculate nucleus responsible for?

A
  • 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
Q

What are the 6 nuclear layers in the lateral genicular even nucleus?

A
  • II, III, V receive signals from lateral half of ipsilateral retina
  • I, IV, VI receive signals from medial half of opposite retina
45
Q

What are layers I and II in the genicular nucleus responsible for?

A
  • 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
Q

What are layers III and VI responsible for in the genicular nucleus?

A
  • parvocellular layers
  • small-medium neurons
  • primarily X ganglion
  • moderate conducting pathway to visual cortex
  • transmits color
  • accurate point to point transmission
47
Q

What is transmission gating?

A

-genicular even nucleus controls how much of the single is allows to pass to the cortex

48
Q

What are the sources of transmission gating?

A
  • 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
Q

What is the primary visual cortex?

A
  • 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
Q

Geniculocalcarine fibers terminate mainly in layer _______.

A

IV

51
Q

What are the subdivisions of layer IV?

A
  • Y ganglion cells terminate in layer IVca

- X ganglion cells terminate in layer IVcB and IVa

52
Q

The visual cortex is organized into several million vertical columns of neurons. How many neurons per column?

A

1000

53
Q

What do color blobs in the columns of secondary visual areas do?

A

-receive lateral signals from adjacent visual columns and are activated specifically by color signals

54
Q

Signals from the two separate eyes enter ____________ stripes of columns in layer IV.

A

Alternating

55
Q

Cortical area deciphers whether the. Retrospective areas of the two visual images from the two separate eyes are in register with each other.

A
  • deciphered info is used to adjust the directional gaze of the eyes
  • required for steropsis
56
Q

Accommodation in children.

A

-refractive power of the lens can voluntarily increase from 20 to 34 diopters (accommodation of 14 diopters)

57
Q

Accommodation in a young person.

A

-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
Q

Which cranial nerve controls both sets of ciliary muscles?

A

3, oculomotor

59
Q

Accommodation in an older person.

A
  • 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

Physiology II Exam 1 (6 decks)

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