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Physiology of the sensory system > 46 & 47 Physiology of visual sensation > Flashcards

46 & 47 Physiology of visual sensation Flashcards

1
Q

What is the unit of power and what is its equation?

A

power = 1/focal length (diopter)

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2
Q

What is focal length?

A

The length between the focal point (fovea) and the lens

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3
Q

The higher the refractive power, the shorter/longer the focal length.

A

shorter

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4
Q

How is accommodation achieved when a person switches to view a near object?

A
  • lateral geniculate nucleus > blurred image perceived in visual cortex > recognised as out of focus > signals from cortex to brainstem at Edinger-Westphal nucleus > signals to ciliary ganglion > ciliary muscles contract > zonular fibers slacken > lens rounded
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5
Q

What is the range of accommodation?

A

Near point - far point

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6
Q

In presbyopia, the range of accommodation increases/decreases because?

A

decreases;

the near point is too far

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7
Q

What happens to the near point and far point in myopia?

A

both too near ;

far point too near is the culprit

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8
Q

What lens shall be worn in myopia?

A

Concave lens

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9
Q

When should convex lens be worn?

A

Hyperopia / Presbyopia

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10
Q

What happen to the near point and far point in hyperopia?

A

near point too far

far point too far (but can be compensated by accommodation

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11
Q

Which are the 5 major layers in the retina?

A
  1. Outer nuclear layer
  2. Outer plexiform layer
  3. Inner nuclear layer
  4. Inner plexiform layer
  5. Ganglion cell layer
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12
Q

In the ______________ layer, retinal ganglion cells make synaptic contacts with bipolar cells and amacrine cells.

A

inner plexiform

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13
Q

In the inner plexiform layer: retinal ganglion cells make synaptic contacts with __________ and __________.

A

Bipolar cells and amacrine cells

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14
Q

Light passes through the layers before/after reaching the photoreceptors.

A

before

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15
Q

Information is modulated by ______________ cells in the ___________layer and are relayed to bipolar cells, then the retinal ganglion cells.

A

horizontal;

outer plexiform

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16
Q

Connection of cone to ganglion cell results in small/big receptive field, and low/high visual acuity.

A

small; high

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17
Q

Multiple rods converging to a single ganglion cell result in a small/big receptive field, and low/high visual acuity.

A

big; low

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18
Q

Photoreceptors have an outer segment which contain the _________________ located on a stack of membranous discs.

A

photosensitive pigment

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19
Q

Rods contains ____________ which contributes to its high sensitivity to light.

A

rhodopsin

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20
Q

Cones contains ___________ thus they have lower sensitivity to light.

A

Iodopsin

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21
Q

Cones are chromatic because?

A

They have multiple types of iodopsins

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22
Q

Which type of photoreceptors have higher convergence of retinal ganglion cells?
This results in lower/higher spatial resolution.

A

Rods;
Cones: one receptive field connect to one retinal cell only ;
lower

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23
Q

Which type of photoreceptors is shorter, thicker and tapered?

A

Cones

rods: long, thin, cylindrical

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24
Q

Single pigment system cannot differentiate colours because both _________ and _____________affects the response.

A

wavelength and intensity

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25
Q

Humans have 3 types of cones, which type is much fewer in number than the other 2?

A

Blue cones

26
Q

Give the 4 possibilities of color weakness.

A
  1. Absence of cones
  2. Just one cone available (monochromatism)
  3. 3rd cone missing (dichromatism)
  4. Abnormality in photopigment (anomalous trichromatism)
27
Q

Red-green color weakness is more/less common than blue color weakness, and is more frequent in males/females.

A

more; males

28
Q

Subtypes of common colour weakness can be tested with the ______________.

A

Ishihara chart

29
Q

In the absence of light, the membrane is _______________ due to _______________. __________ pump maintains the concentration gradient

A

depolarised; high level of Na+ current flowing into the outer segment.;

Na/K+ pump

30
Q

In bright light, the membrane is more _____________, because _________________.

A

hyperpolarized,;

the Na+ channels are closed

31
Q

Give the flow of events happening when light is shone on the retina.

A

Light activates transducin (G-protein) > activates cGMP phosphodiesterase > break down cGMP > Na+ channels close > membrane hyperpolarization > less glutamate release

32
Q

The Na+ channels in the membrane is kept opened by?

A

cGMP

33
Q

Glutamate is inhibitory to ___________ cells.

A

On center bipolar cells

34
Q

Glutamate is excitatory to _____________ cells.

A

Off center bipolar cells

35
Q

Surround photoreceptors are associated with _________ cell. In dark light, it will cause ___________ to photoreceptor, and more/less glutamate release from the photoreceptor to the __________ cell. The __________ cell in turn release more/less inhibitory NT , causing the on center// off center bipolar cell to __________ respectively.

A 
horizontal;
depolarization;
more;
horizontal; horizontal;
more;

less glutamate release
on center: depolarised;
off center: hyperpolarized

36
Q

Retinal ganglion cells with small receptive fields (P cells) receiving main inputs from _________ cells are concentrated in the _______.

A

cones;

fovea

37
Q

Retinal ganglion cells with ________ receptive fields (__ cells)are found more in the periphery.

A

large;

M

38
Q

What type of retinal ganglion cell is intrinsically sensitive to light ?

It plays a role in ____________ by their direct projection to the ___________ nucleus of the hypothalamus, also mediating light reflex.

A

Photosensitive melanopsin;
circadian rhythm;
suprachiasmatic

39
Q

State the route of the visual pathway from nerve fibers leaving the eye to the cortex.

A

> Optic chiasm > cross-over medial bundles > lateral geniculate nuclei > optic radiation > primary visual cortex (V1)

40
Q

_____________ cells project to the parvocellular layers of the lateral geniculate nucleus consisting of small cells.

A

Retinal P cells

41
Q

M cells project to ____________ layers of the lateral geniculate nucleus consisting of larger cells.

A

Magnocellular

42
Q

Majority of neurons in primary visual cortex are specialized in detecting ________________ and their _________, and properties like color.

A

line contrast of specific orientation;

movements

43
Q

Neurons in primary visual cortex are named ________ cells.

A

Simple and complex

44
Q

Contour detection by the primary visual cortex is achieved by convergence of inputs from the ______________ into _____________.

A

Lateral genicular nucleus nuerons into one simple cell in V1

45
Q

What are complex cells?

A

While simple cells respond maximally to a bar at a preferred orientation in a specific location, one type of complex cells have a larger receptive field which are orientation-sensitive but location-insensitive

46
Q

__________________ represents the initial site of analysis of visual images.

A

Primary visual cortex (V1, area 17)

47
Q

The primary visual cortex projects to the ____________________ for further visual processing, from there to visual association cortex and higher visual areas.

A

Extrastriae visual cortex

48
Q

What does the dorsal stream detect and via what to reach its final destination?

A

Where?;

via middle temporal visual area (V5) to the posterior parietal cortex.

49
Q

What is V5? Which pathway is it involved?

Lesion?

A 
Middle temporal (MT) visual area;
dorsal pathway (where);
V5: for analysis of motion, seeing world in series of snapshots
50
Q

What will happen with damage to the parietal lobe?

A

Hemineglect syndrome, tendency to ignore the contralateral side.

51
Q

What does the ventral stream detect and via what to reach its final destination?

A

What?

via V4 to the inferior temporal cortex

52
Q

Function of fusiform gyrus?

Neurons there have small/large receptor field, therefore?

A

recognition of face;

large, can code an code different sizes of the faces reflecting different distance from the subject

53
Q

Spatial orientation, depth perception, location of objects is detected in which pathway?

A

Where pathway

also movement of objects

54
Q

What pathway detects what features of vision?

A

Color and shape, important in language ability.

55
Q

Describe the flow of events in pupillary reflex.

A

When light shines onto retina > signals project to pretectal area > Edinger-Westphal nucleus > send out to contract the sphincter muscles > decrease size of pupil

56
Q

Why pupillary reflex is consensual?

A

Due to the bilateral projection of the pretectal nucleus of one side to Edinger-Westphal nucleus on both sides.

57
Q

Briefly describe what is glaucoma.

A

Excess aqeuous fluid in anterior chamber of the eye, retinal ganglion cells and axons degenerates, causing tunnel vision then blindness

58
Q

How can cataract be treated?

A

Lens become cloudy, replacement by artificial lens.

59
Q

What is macular degeneration? Will it cause whole-blindness?

A

Atrophy of neural tissue or severe haemorrhage diseases at the macula (includes fovea).
No, peripheral vision is not affected.

60
Q

_____________ is progressive degeneration of the retina resulting from diabetes mellitus. Blood vessels burst and neural cells die.

A

Diebetic retinopathy

61
Q

In retinal detachment, _______ becomes separated from the _________.

A

Retina; choroid

Physiology of the sensory system (7 decks)

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