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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
Membrane is leaky to sodium ions that flow back in through opened cGMP-gated channels when...?
exposed to darkness; neutralize negativity on inside of cell
26
Under dark conditions, what is the membrane potential?
-40mV rather than expected -70mV
27
What is the series of events that occurs after the outer segment is exposed to light?
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
True or False? | Retinal portions of the rods and cones are different?
false, retinal portions are the same
29
What colors are cones sensitive to?
blue, green, and red
30
What are the layers of the retina?
photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells
31
What are the two photoreceptors?
rods and cones
32
What do photoreceptors synapse with?
bipolar cells and horizontal cells
33
True or False? | Output from horizontal cells is always inhibitory.
true (lateral inhibition)
34
Bipolar cells transmit signals to inner plexiform layer and synapse with what?
amacrine and ganglion cells
35
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?
ganglion cells or to other amacrine cells
36
Ganglion cells transmit signals from?
retina to brain Note: only retinal cells to transmit action signals
37
What type of cells make up the optic nerve?
ganglion cells
38
In regards to the foveal region (cone vision), what are the three neurons in the direct pathway?
cones, bipolar cells, ganglion cells
39
In regards to the foveal region, what are the four neurons that make up pure rod vision?
rods, bipolar cells, amacrine cells, ganglion cells
40
What NT do rods and cones secrete to bipolar cells?
glutamate
41
What are the NTs of amacrine cells?
8 or more including: GABA, glycine, dopamine, acetylcholine, indolamine (all inhibitory)
42
Most amacrine cells are interneurons that help analyze what?
visual signals before they leave the retina
43
How many kinds of amacrine cells are there?
30
44
On average how many rods and how many cones converge on each ganglion cell and the optic nerve?
60 rods, 2 cones
45
Approaching the fovea, fewer rods and cones converge on each optic fiber and rods and cones become more slender. Why is this?
increases visual acuity in central retina
46
Gangion cells in the peripheral retina are more sensitive to what?
weak light
47
What are W ganglion cells?
make up 40% of all ganglion cells, small, receive excitation from rods, dendrites spread widely in the inner plexiform layer
48
What are X ganglion cells?
make up 55% of all ganglion cells, medium diameter, transmit signals 14m/sec, responsible for all color vision
49
What are Y ganglion cells?
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
Describe the dorsal lateral geniculate nucleus
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
Describe layers I and II of the dorsal lateral geniculate nucleus
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
Describe layers III through VI of the dorsal lateral geniculate nucleus
contain small to medium size neurons, receive input almost entirely from X type ganglion cells, transmits color, accurate point to point transmission
53
What is transmission gating in the dorsal lateral geniculate nucleus? What is the source of gating control?
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
Where is the primary visual cortex and what does it do?
located in occipital lobes, signals from macular area terminate near the occipital pole
55
How many layers are there in the primary visual cortex
6
56
How is the primary visual cortex organized?
into several million vertical columns of neurons
57
What occurs in layer IV of the primary visual cortex?
signals from the two separate eyes enter alternating stripes of columns
58
What does the cortical area of the primary visual cortex decipher?
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
What is accommodation in children?
refractive power of the lens can be voluntarily increased from 20 to 34 diopters (an accommodation of 14 diopters)
60
Describe accommodation in young people?
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
Describe accommodation in older people
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
Rhodopsin + light = scotopsin + all-trans retinal What was converted to form all-trans retinal?
11-cis retinal is converted to all-trans retinal and dissociates from scotopsin
63
For all-trans retinal to covert back to 11-cis retinal, what is required?
Isomerism and metabolic energy
64
True or false? | In the central fovea there are only rods, not cones
False, only cones

Physiology II (19 decks)

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