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Physio Test 4 > Vision > Flashcards

Vision Flashcards

1
Q

What is the light sensitive portion of the eye?

A

Retina

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2
Q

What photoreceptor provides high visual acuity?

A

Cones

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3
Q

What photoreceptor provides low visual acuity but high sensitivity?

A

Rods

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4
Q

What photoreceptor is responsible for daylight (photopic) and color vision?

A

Cones

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5
Q

What photoreceptor is responsible for dim light (scotopic), colorless vision?

A

Rods

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6
Q

What is the duplicity theory of vision?

A

The idea that vision is mediated by two photoreceptors: rods in low light and cones in bright light

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7
Q

How many layers does the retina have? How many do we consider in class?

A

Total: 10 layers but in class we only touch on 4

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8
Q

What are the 4 layers of the retina?

A

1) Pigment Epithelium
2) Photoreceptor layer
3) Bipolar layer
4) Ganglion cell layer

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9
Q

Cells of the pigment epithelium layer contain _______ which makes them appear black.

A

Melanin

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10
Q

Wat is the function of the pigmented epithelium?

A

1) Capture stray light

2) Storehouse of Vitamin A for exchange with photoreceptors

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11
Q

What 3 neurons are found in the bipolar cell layer?

A

1) Bipolar cells
2) Horizontal cells
3) Amacrine cells

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12
Q

What cells of the bipolar layer connect rods and cones with ganglion cells?

A

Bipolar cells

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13
Q

What cells of the bipolar layer make photoreceptor to photoreceptor connections?

A

Horizontal cells

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14
Q

What cells of the bipolar layer are located at the scleral border?

A

Horizontal cells

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15
Q

What cells of the bipolar layer are located at the corneal side?

A

Amacrine cells

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16
Q

What cells of the bipolar layer makes complex horizontal connections between bipolar cells and also connect bipolar cells to ganglion cells?

A

Amacrine cells

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17
Q

What cells transmit information from the retina to form the optic nerve and optic tract?

A

Ganglion cells

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18
Q

The axons of ganglion cells leave the retina at the ___________________.

A

Optic disc

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19
Q

What is the central, cone-rich region of the retina?

A

Macula lutea

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20
Q

What lies at the center of the macula and is the region of highest visual acuity?

A

Fovea centralis

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21
Q

Where is the ONLY place in the retina where light has direct access to photoreceptors without having to pass through other layers?

A

Fovea centralis

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22
Q

What is located nasally to the fovea and is the site where ganglion cell axons exit the eye as the optic nerve?

A

Optic disc

23
Q

Are there any photoreceptors at the optic disc?

A

NO - this is the blind spot of the eye

24
Q

What are the two parts that make up visual pigments?

A

Chromophore and an opsin.

25
Q

What is a chromophore?

A

The light absorbing part of the visual pigment molecule. IT consists of 11-cis retinal

26
Q

What is an opsin?

A

It is a colorless protein that binds to the chromophore and imparts spectral sensitivity to visual pigment

27
Q

What is the rods visual pigment and what is it made up of?

A

Visual pigment: rhodopsin

Chromophore - 11-cis retinal
Opsin - scotopsin

28
Q

What is the cones visual pigment and what is it made up of?

A

Since there are 3 primary colors each of them contains an 11-cis retinal but each one contains a differnt opsin (all are photopsins)

29
Q

What causes color blindness?

A

Loss of one or more color pigments or spectral proximity

30
Q

Loss of spectral proximity causes ________________.

A

Color blindness

31
Q

What do these visual pigments do?

A

CHange light into an electrical signal

32
Q

What occurs when light hits these visual pigments? (use example of rods)

A

Light causes 11-cis form of retinal to be converted to all trans retinal. This all trans form can no longer bind with scotopsin and they begin to separate forming intermediates that finally produce Metarhodopsin II. This product produces electrical changes in the rods and slowly decays to retinal and opsin which are then recycled to produce rhodopsin.

33
Q

Metarhodopsin II reduces the _____ current in the outer segment.

A

Dark current

This current is caused by high conductance to Na+. This means that metarhodopsin II causes decreased Na+ conductance

34
Q

What does the reduction of dark current by metarhodopsin II do?

A

Causes hyperpolarization as the membrane potential moves closer to Ek.

35
Q

What is the mechanism by which metarhodopsin II reduces dark current?

A

Metarhodopsin II activates G proteins called transducin. This active transducin stimulates a phosphodiesterase molecule and each phosphodiesterase molecule hydrolyzes many cGMP molecules. This decrease in cGMP causes the Na+ channels to close causing hyperpolarization.

36
Q

What do the rods do in response to light?

A

Light causes hyperpolarization of rods. This is a graded response which means that the more light there is, the greater the hyperpolarization. This hyperpolarization leads to decreased output of transmitter, glutamate, by the rods.

37
Q

How does the bipolar cells react to light?

A

There are two types of bipolar cells, one that depolarizes and one that hyperpolarizes in reponse to light. The amount of excitatory transmitter released by the bipolar cell to the ganglion cell increases if it is depolarizes or decreases if the bipolar cell hyperpolarizes.

38
Q

The retina contains about 125 million rods and 5 million cones but only 1.6 million ganglion cells. What does this tell us?

A

This tells us that there are many connections of rods and cones to a single ganglion cell. On average each ganglion cells receives input from many photoreceptors which allows for weak signals to be summated thus increasing sensitivity. This is known as convergence.

39
Q

In the _________ there is a 1 to 1 cone to ganglion cell relationship with no rods present.

A

Foveola (fovea centralis)

This allows for higher visual acuity by decreased sensitivity

40
Q

Explain the idea of the circuitry of the ganglion center and surround.

A

Center is formed by photoreceptor -> bipolar cell -> ganglion cell

Surround is formed by connections of photoreceptors in the surround to photoreceptors in the center via horizontal cells. photoreceptor -> bipolar cell -> photoreceptor

41
Q

Light in the surround causes horizontal cells to ______________ photoreceptors in the center.

A

depolarize

42
Q

The surround is thus always ______________ to the center since depolarization is the opposite of the effect produced by light.

A

antagonistic

43
Q

What are the type of ganglion cells?

A

1) M cells
2) P cells
3) intrinsically photosensitive retinal ganglion cells (ipRGCs)

44
Q

What cells of the ganglion cell layer has large receptive fields which encodes information about general location of an object in a receptive field?

A

M cells

45
Q

Are M cells sensitive to color?

A

Little or no sensitivity to color. But they are sensitive to movement and to small differences in contrast

46
Q

Where do these M cells project to?

A

Two ventral layers of the lateral geniculate nucleus (magnocellular division)

47
Q

Which cells of the ganglion cell layer has a small receptive field with high spatial resolution and encodes fine details?

A

P cells

48
Q

Are P cells sensitive to anything?

A

Colors

49
Q

Where do these P cells project to?

A

4 dorsal layers of the Lateral geniculate nucleus (Parvocellular areas)

50
Q

Which of the 3 ganglion cells make up only a small percentage of the cells in this layer?

A

ipRGCs

51
Q

Which of the cells of the ganglion layer contains melanopsin (a photopigment) which allows them to respond directly to light?

A

ipRGCs

52
Q

Are ipRGCs more or less sensitive to light than rods or cones? Why?

A

Less sensitive due to the low pigment density

53
Q

What is the response of ipRGCs to light?

A

They respond to light by causing depolarization (opposite of cones and rods)

54
Q

Which cells are involved in pupillary light reflexes and circadian photo entrainment?

A

ipRGCs

Physio Test 4 (5 decks)

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