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Neuroscience > NEUR 0010 - Chapter 9 > Flashcards

NEUR 0010 - Chapter 9 Flashcards

1
Q

What does the retina actually process, rather than a faithful representation of light intensity?

A

Differences in light intensity on different parts of it

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2
Q

What is the LGN?

A

First synaptic relay in the visual perception pathway; in thalamus; receives info from the optic nerves and sends it to the cerebral cortex

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3
Q

Why does the pupil appear dark?

A

Because of the light-absorbing retina that’s behind it

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4
Q

The cornea is continuous with what part of the eye?

A

The sclera

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5
Q

What are extraocular muscles?

A

Three pairs of muscles in the sclera

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6
Q

What is the sclera?

A

The white of the eye; tough outer wall of the eyeball

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7
Q

What is the conjunctiva?

A

The membrane that folds back from the eyelid inside and joins with the sclera

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8
Q

What is the macula?

A

The part of the retina used for central vision; distinguished by yellow color and lack of large blood vessels

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9
Q

What is the fovea?

A

A dark spot in the macula where the retina is thinner; marks the center of the retina, and so delineates nasal vs temporal retina

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10
Q

What are two specializations of the part of the retina dedicated to central vision?

A

Lack of large blood vessels, fovea is thinner

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11
Q

What is interesting about the nutrient system of the cornea?

A

Has no blood vessels, so receives nutrients from the aqueous humor behind it

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12
Q

What is the lens? How is its size controlled?

A

Behind the iris: suspended by zonule fibers that are attached to ciliary muscles

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13
Q

How is focal distance related to curvature of the lens?

A

The greater the curvature, the smaller the focal distance

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14
Q

What is the focal distance?

A

The distance from the refractive surface to the point at which refracted light rays converge

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15
Q

How does lens accommodation work?

A

The ciliary muscles contract and swell, loosening the zonule fibers and allowing the lens to thicken; or the ciliary muscles relax and the diminish, tightening the zonule fibers and forcing the lens to thin

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16
Q

What does it mean that the pupillary light reflex is consensual?

A

If you trigger a response in one eye, it happens in both eyes: one pupil won’t dilate without the other, etc.

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17
Q

Lack of consensual response for pupillary light reflex signifies a neurological disorder of what brain region?

A

Brainstem

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18
Q

What effect does pupil constriction have?

A

Increasing depth of focus (reduces blurriness of far objects)

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19
Q

What are two factors that affect visual acuity?

A

Spacing of photoreceptors in the retina; precision of the eye’s refraction

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20
Q

What is the most direct pathway for visual information to exit the eye?

A

From photoreceptors to bipolar cells to ganglion cells

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21
Q

Which retina cells fire action potentials?

A

Just the ganglion cells

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22
Q

What are horizontal cells?

A

Receive input from the photoreceptors, project neurites laterally to influence surrounding bipolar cells and photoreceptors

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23
Q

What are amacrine cells?

A

Receive input from bipolar cells, project neurites laterally to influence surrounding ganglion cells, bipolar cells, and other amacrine cells

24
Q

What is the laminar organization of the retina from inner to outer?

A

Ganglion cell layer, inner plexiform layer (amacrine-ganglion/bipolar/amacrine synapses); inner nuclear layer (bipolar cells); outer plexiform layer (horizontal-bipolar/photoreceptor synapses); outer nuclear layer (photoreceptor cell bodies); layer of photoreceptor outer segments; pigmented epithelium

25
Q

Why is it a good thing that the laminar organization is seemingly backwards?

A

It’s good to have the pigmented epithelium at the bottom: helps maintain photoreceptors, absorbs any extra light and minimizes reflection

26
Q

What is the significance of the greater number of photopigmented disks in rods?

A

Higher photopigment concentration, so MUCH more sensitive to light

27
Q

What are the characteristics of the peripheral retina pertaining to rods/cones and photoreceptors/ganglion cells?

A

More rods than cones; higher photoreceptor/ganglion ratio

28
Q

What is more sensitive to light levels, peripheral retina or fovea?

A

Peripheral retina: more rods

29
Q

What is the significance of the pit-like structure of the fovea?

A

Clears the other layers out of the way to allow for better acuity

30
Q

What is the basic mechanism for signal transduction in the visual system?

A

G-proteins

31
Q

What is the Vm for a rod outer segment in complete darkness?

A

-30 mV

32
Q

Why is the Vm of a rod outer segment in darkness higher than usual?

A

Dark current from Na+ leak in from cGMP channels

33
Q

Where does the cGMP come from for the dark current?

A

Made by guanylyl cyclase in the cytoplasm

34
Q

What is the pigment in rods that responds to light?

A

Rhodopsin

35
Q

What does it mean that rhodopsin can be thought of as “a receptor protein with a pre-bound chemical agonist?”

A

Receptor protein is opsin like a normal GPCR; pre-bound agonist is retinal (derivative of vitamin A)

36
Q

What happens when light hits rhodopsin?

A

Changes from purpose to yellow: stimulates GP called transducin in the disk membrane; activates PDE to break down cGMP; no dark current; hyperpolarization

37
Q

Why does daylight vision depend entirely on cones?

A

Because the rods hit a point of saturation where they can’t be hyperpolarized anymore

38
Q

What is the peak sensitive of rods? What color is this?

A

500 nm, blue-green

39
Q

What contributes to dark adaptation?

A

Pupil dilation; and when that maxes out: regeneration of unbleached rhodopsin and adjustment of functional circuitry of retina (make info from more rods available to each ganglion cell)

40
Q

What is Ca++’s role in light adaptation?

A

If immediate light, then hyperpolarized as much as possible to Ek; gradually depolarizes back to -35 mV because lack of Ca++ entry to inhibit cGMP (so more cGMP is made and the Na+/Ca++ channels open back up and allow depolarization

41
Q

What is Ca++’s effect on guanylyl cyclase?

A

Inhibits: prevents cGMP production

42
Q

When does a photoreceptor release neurotransmitter, light or dark?

A

Dark: preferred stimulus

43
Q

What does it mean to be an OFF bipolar cell or an ON bipolar cell?

A

Different responses ot glutamate released by photoreceptors

44
Q

What is an OFF bipolar cell?

A

Glutamate-gated cation channels mediate classic depolarizing EPSP from influx of Na+

45
Q

What is an ON bipolar cell?

A

GPCRs respond to glutamate by hyperpolarizing

46
Q

Why are bipolar cells called off or on? What does that refer to?

A

When they depolarize: OFF bipolar cells depolarize when light is off (more glutamate allows for influx of Na+, causing depolarization); ON bipolar cells depolarize when light is on (less glutamate released, since glutamate causes hyperpolarization)

47
Q

What is the receptive field of a bipolar cell?

A

The area of the retina that, when stimulated with light, changes the cell’s membrane potential

48
Q

What is the relationship between response of bipolar center vs surround?

A

Opposite effects

49
Q

What does it mean to say that ganglion cells are ON-center or OFF-center?

A

ON-center ganglion cells receive input from an ON-center bipolar cell, and the opposite for OFF

50
Q

What kind of visual information do ganglion cells respond to?

A

Differences in light intensity

51
Q

What are the two main types of ganglion cell?

A

M and P

52
Q

How do M cells differ from P cells?

A

Less numerous; larger receptive fields; conduct APs more rapidly; more sensitive to low-contrast stimuli

53
Q

What is the difference in AP firing between M and P cells?

A

M is transient burst, P is sustained discharge

54
Q

What are color-opponent cells?

A

Color-sensitive ganglion cells that can detect difference in wavelength; can be P or nonPnonM

55
Q

What are the two types of color-opponent cells?

A

Red-green and Blue-yellow

56
Q

Why aren’t M cells color-opponent?

A

Receive input from multiple types of cones

57
Q

Why are P and nonPnonM cells color-opponent?

A

The center of the receptive field is fed mainly by one type of cone

Neuroscience (19 decks)

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