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Physiology II > Vision (Lec 5) > Flashcards

Vision (Lec 5) Flashcards

1
Q

Define refraction

A

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

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2
Q

What happens to light that strikes perpendicular surface?

A

continues on without bending

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3
Q

Refractive power measures what?

A

how mucha lens bends light waves; 1 diopter = 1 meter divided by focal length

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4
Q

What occurs at the focal point?

A

parallel rays of light pass through after passing through each part of lens

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5
Q

What does the iris of the eye do?

A

controls amount of light entering eye

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6
Q

Depth of focus of the lens increases when the pupillary diameter increases or decreases?

A

decreases

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7
Q

Define emmetropia

A

normal eyes with regard to depth of focus

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8
Q

Define hyperopia

A

farsightedness: eyeball that is too short or lens system is too week; all distant objects can be seen clearly

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9
Q

Define myopia

A

nearsightedness; too long of an eyeball; light rays are focused in front of the retina

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10
Q

What is visual acuity?

A

measure of the resolving power of the eye

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11
Q

What is the average diameter of a cone in the retina?

A

1.5 micrometers

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12
Q

What is aqueous humor in the eye formed by?

A

ciliary processes

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13
Q

What space in the eye are Na+, Cl-, and HCO3- actively transported into?

A

ciliary apparatus

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14
Q

After Na+, Cl-, and HCO3- draw water into ciliary apparatus, where does the aqueous solution pass into?

A

anterior chamber

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15
Q

Fluid in the eye flows from the anterior chamber into what?

A

the canal of schlemm and from there into aqueous veins in the sclera

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16
Q

What is the normal intraocular pressure?

A

15 mm Hg

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17
Q

What is the photosensitive pigment found in rods?

A

Rhodopsin

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18
Q

What is the photosensitive pigment found in cones?

A

three different color pigments (transmembrane conjugated proteins)

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19
Q

Outer segment vs. inner segment of the rod and the cone

A

outer segment: light-sensitive photochemicals

inner segment: contains organelles, especially mitochondria

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20
Q

Scotopsin + 11-cis retinal = ?

A

Rhodopsin

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21
Q

Metarhodopsin II is an intermediate in the Rhodopsin pathway that does what?

A

excites electrical changes in the rods

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22
Q

When exposed to light, excitation of the rod causes what?

A

hyperpolarization

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23
Q

When exposed to light, decomposition of rhodopsin decreases what?

A

rod membran conductance for Na+ ions in the outer segment -> results in hyperpolarizaiton of entire rod membrane

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24
Q

The inner segment of the rod continually pumps ___ from inside rod to outside and ___ in the opposite direction.

A

Na+; K+

note: negative potential is created on the inside of the cell

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25
Q

Membrane is leaky to sodium ions that flow back in through opened cGMP-gated channels when…?

A

exposed to darkness; neutralize negativity on inside of cell

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26
Q

Under dark conditions, what is the membrane potential?

A

-40mV rather than expected -70mV

27
Q

What is the series of events that occurs after the outer segment is exposed to light?

A

rhodopsin decomposes, rhodopsin complex is activated and stimulates tranducin (G-protein) which activates cGMP phophdiesterase which catalyzes cGMP -> 5’GMP, reduction in cGMP causes closure of Na+ channels which causes photoreceptor to become hyperpolarized

28
Q

True or False?

Retinal portions of the rods and cones are different?

A

false, retinal portions are the same

29
Q

What colors are cones sensitive to?

A

blue, green, and red

30
Q

What are the layers of the retina?

A

photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells

31
Q

What are the two photoreceptors?

A

rods and cones

32
Q

What do photoreceptors synapse with?

A

bipolar cells and horizontal cells

33
Q

True or False?

Output from horizontal cells is always inhibitory.

A

true (lateral inhibition)

34
Q

Bipolar cells transmit signals to inner plexiform layer and synapse with what?

A

amacrine and ganglion cells

35
Q

Amacrine cells transmit signals directly from bipolar to ganglion cells or within the inner plexiform from axons of bipolar cells to dendrites of what two cell types?

A

ganglion cells or to other amacrine cells

36
Q

Ganglion cells transmit signals from?

A

retina to brain

Note: only retinal cells to transmit action signals

37
Q

What type of cells make up the optic nerve?

A

ganglion cells

38
Q

In regards to the foveal region (cone vision), what are the three neurons in the direct pathway?

A

cones, bipolar cells, ganglion cells

39
Q

In regards to the foveal region, what are the four neurons that make up pure rod vision?

A

rods, bipolar cells, amacrine cells, ganglion cells

40
Q

What NT do rods and cones secrete to bipolar cells?

A

glutamate

41
Q

What are the NTs of amacrine cells?

A

8 or more including: GABA, glycine, dopamine, acetylcholine, indolamine (all inhibitory)

42
Q

Most amacrine cells are interneurons that help analyze what?

A

visual signals before they leave the retina

43
Q

How many kinds of amacrine cells are there?

A

30

44
Q

On average how many rods and how many cones converge on each ganglion cell and the optic nerve?

A

60 rods, 2 cones

45
Q

Approaching the fovea, fewer rods and cones converge on each optic fiber and rods and cones become more slender. Why is this?

A

increases visual acuity in central retina

46
Q

Gangion cells in the peripheral retina are more sensitive to what?

A

weak light

47
Q

What are W ganglion cells?

A

make up 40% of all ganglion cells, small, receive excitation from rods, dendrites spread widely in the inner plexiform layer

48
Q

What are X ganglion cells?

A

make up 55% of all ganglion cells, medium diameter, transmit signals 14m/sec, responsible for all color vision

49
Q

What are Y ganglion cells?

A

Make up about 5% of all ganglion cells, large diameter, transmit signals 50 m/sec, apprise the CNS almost instantaneously when a new visual event occurs

50
Q

Describe the dorsal lateral geniculate nucleus

A

receives input from optic nerve, relays information from optic tract to visual cortex by way of optic radiation, 50% decussation in optic chasm, six nuclear layers in lateral geniculate nucleus

51
Q

Describe layers I and II of the dorsal lateral geniculate nucleus

A

contain large neurons, receive input from large type Y ganglion cells, provides rapidly conducting pathway to visual cortex, transmits only black and white, point to point transmission is poor

52
Q

Describe layers III through VI of the dorsal lateral geniculate nucleus

A

contain small to medium size neurons, receive input almost entirely from X type ganglion cells, transmits color, accurate point to point transmission

53
Q

What is transmission gating in the dorsal lateral geniculate nucleus? What is the source of gating control?

A

lateral geniculate nucleus controls how much of the signal is allowed to pass to the cortex

Gating control: corticofugal fibers from primary visual cortex and reticular areas of the mesencephalon

54
Q

Where is the primary visual cortex and what does it do?

A

located in occipital lobes, signals from macular area terminate near the occipital pole

55
Q

How many layers are there in the primary visual cortex

A

6

56
Q

How is the primary visual cortex organized?

A

into several million vertical columns of neurons

57
Q

What occurs in layer IV of the primary visual cortex?

A

signals from the two separate eyes enter alternating stripes of columns

58
Q

What does the cortical area of the primary visual cortex decipher?

A

whether the respective areas of the two visual images from the two separate eyes are in register with each other - used for directional gaze of the separate eyes, stereopsis

59
Q

What is accommodation in children?

A

refractive power of the lens can be voluntarily increased from 20 to 34 diopters (an accommodation of 14 diopters)

60
Q

Describe accommodation in young people?

A

when the lens is in a relaxed state with no tension on its capsule, it assumes an almost spherical shape; suspensory ligaments attached radially around the lens create a tension that causes the lens to remain relatively flat under normal eye conditions

61
Q

Describe accommodation in older people

A

lens becomes larger and thicker with age, lens becomes less elastic with age, power of accommodation decreases to less than 2 diopters by the age of 45 to 50 and it decreases to 0 by the age of 70, presbyopia

62
Q

Rhodopsin + light = scotopsin + all-trans retinal

What was converted to form all-trans retinal?

A

11-cis retinal is converted to all-trans retinal and dissociates from scotopsin

63
Q

For all-trans retinal to covert back to 11-cis retinal, what is required?

A

Isomerism and metabolic energy

64
Q

True or false?

In the central fovea there are only rods, not cones

A

False, only cones

Physiology II (19 decks)

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