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physio > vision > Flashcards

vision Flashcards

1
Q

function of anterior compartmetn lens system of the eye

A

focus lgiht on retina

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2
Q

function of posterior compartment of the eye

A

transduce light into electricl signal

project visual signal to cortex

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3
Q

center of the retina, color vision, only cones present, highest visual acuity

A

fovea

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4
Q

what do clinicans use to look at increased optic pressure?

A

optic disc

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5
Q

what is responsible for the blood supply to the retina?

A

optic disc

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6
Q

optic disc with an inverted, diffuse margin

A

glaucoma

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7
Q

optic disc with an everted, diffuse margin

A

papilledema

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8
Q

What is the light sensitive region of the eye?

A

retina

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9
Q

How many cones in the retina?

A

3 million

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10
Q

what are cones and rods responsible for?

A

cones- color

rods- night

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11
Q

abundant photopigment, high sensitivity, saturated in daylight, slow response, 1 visual pigment

A

rods

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12
Q

low sensitivity, less photopigment, fast response, 3 visual pigments

A

cones

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13
Q

What is the visual pigment cycle?

A
  1. rods (and cones) contain visual pigment- light causes photoactivation (11-cis to all-trans retinal)
  2. metarhodopsin II (all trans config) triggers phototransduction
  3. Rhodopsin contains scotopsin and visual pigment
  4. all-trans retinal recycled by isomerase to 11-cis retinal
  5. 11-cis configuration required to bind scotopsin
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14
Q

vitamin A

A

precursor for all-trans retinal

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15
Q

what catalyzes conversion to retinal?

A

retinol dehydrogenase

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16
Q

vitamin A deficiency

A

causes decrease all-trans retinal and decrease in rhodopsin cuasing night blindess- poor senstitivty in dim light

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17
Q

how do rods depolarize in dark?

A

cGMP- gated channels open which allow sodium influx (‘dark current’)
glutamate released

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18
Q

What closes the cGMP-gated channels?

A

rhodopsin photoactivation

sodium influx stops causing hyperpolarization

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19
Q

What is the mechanism for phototransduction?

A
  1. rhodopsin bleaching activates transducin
  2. transducin activates cGMP PDE to degrade cGMP to 5’-GMP
  3. [cGMP] decreaases
  4. cGMP channel closes
  5. Rod hyperpolarizes and neurotransmitter terminated
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20
Q

What allows difference in the 3 scotopsins’ wavelengths?

A

slight amino acid differences

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21
Q

Tuning allows

A

each cone to have an absorbance maximum for particular wavelengths of light

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22
Q

What are the normal cone spectral sensitivty peaks for each color?

A

blue- 437
green- 533
red- 564

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23
Q

What is true color blindess and what is the cause?

A

a mutation causing complete lack of a cone

X chromsome

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24
Q

What is color deficiency?

A

less severe mutation causing a shift of absorbance spectrum

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25
Q

Deuteranomaly

A

green cone peak sensitivity is shifted toward red (5% males)

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26
Q

protanomaly

A

red cone peak shifted towards green (1% males)

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27
Q

Signals (except GC) are propagated by

A

electrotonic conduction

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28
Q

photoreceptors synapse on

A

bipolar cells and HC cells

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29
Q

Bipolar cells synapse on

A

ganglion cells with axons and ‘true’ action potentials

amacrine cells

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30
Q

retinal sensitivity increases 10,000 at 40 min dark

A

rods

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31
Q

dark adaption 4x faster; saturation

A

cones

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32
Q

what phosphorylates rhodopsin producing and adaption mechanism for regulating light sensitivity (light adaption)?

A

rhodopsin kinase

33
Q

lateral inhibition enhances what?

A

contrast

34
Q

horizantal cells main mediator of lateral inhibition

A

pr synapse on adjacent BCs

inhibition by GABA

35
Q

prevents lateral spread of light excitation on retina

A

horizantal cells

36
Q

creates on/off organization; typical feature of sensory systems

A

horizontal cells

37
Q

lateral inhibition: color opponency

A

horizantal cells release of GABA on adjacent PR terminals ( opens Cl- channels) and opposes color signal

38
Q

off-center BCs via..

A

typical glutamate receptors

hyperpolarize in light

39
Q

On-center BCs express..

A

mGluR6 which maintains TRMP1 in a closed state

40
Q

What relieves the glutamate inhibition and opens the TRPM1 channels

A

light

41
Q

optic nerves are always

A

ipsilateral

42
Q

once it reaches optic chiasm, optic nerve is refferred to as..

A

optic tract

43
Q

What are the two pathways that optic radiation LGN axons project to?

A

parietal and temporal

44
Q

superior visual field goes to

A

inferior retina–> inferior visual cortex

and vis versa

45
Q

Functions of LGN

A
  1. projects visual scene to primary visual cortex via optic radiation or geniculocalcarine tract
  2. LGN ‘gates’ transmission of signals to visual cortex
  3. LGN may receive input from superior colliculus
46
Q

2 innermost layers of the LGN

A

M-cells

47
Q

4 outermost layers of LGN

A

P-cell

48
Q

What is adjacent tot the primary visual cortex (area 17)?

A

calcarine fissure

49
Q

Area 18 is responsible for higher order visual informaiton processing; what is this area called?

A

secondary visual cortex

50
Q

left visual field projects to…

A

right primary visual cortex

51
Q

Ocular Dominance Column

A

loss of input from the right eye (enucleation)- alternating visual input from left and right eyes causes this specific projection pattern in the right primary visual cortex (area 18 interprets these two field)- appears like a zebra pattern

52
Q

M path superior termination

A

area 18/ POT for 3d position, shape, and motion

53
Q

P path inferior termination

A

temporal lobe for fine detail and color information

54
Q

What cells respond to specific orientation or direction and where does it occur?

A

simple cells

layer IV

55
Q

Distal to layer VI, some neurons sensitive only to directional movement across the image

A

complex cells

56
Q

most distal cortical layers, some neurons only respond to specific line lengths, angles and velocities

A

hypercomplex cells

57
Q

specific neuronal polls are sensitive to specific image features

A

generalization

58
Q

What fibers from GLN convey color signals and fine details?

A

P fibers

59
Q

P fibers form LGN project where?

A

to sublayers a and cbeta in layer IV

60
Q

voluntary fixation area (frontal eye field)

A

bilateral premotor cortex for voluntary control EOM

61
Q

involuntary fixation area (area 18)

A

bilateral to automatically ‘lock’ eyes on target

62
Q

What are the three types of eye movement?

A
  1. continuous tremor
  2. slow drift
  3. flicking movement
63
Q

What type of eye movement is lost with lesion to the superiror colliculus?

A

flicking movement

64
Q

What is used to test for ‘pursuit movement’?

A

opticokinetic drum

65
Q

Saccades are also referred to as …

A

anticipatory jumps

66
Q

What are the 6 EOMs and the pairs?

A
  1. superior and inferior recti move eyes up and down
  2. medial and lateral recti move eyes side to side
  3. superior and inferior obliques rotate the eye
67
Q

What cranial nerve is the lateral rectus controlled by?

A

6

68
Q

What cranial nerve is the superior oblique controlled by?

A

4

69
Q

What cranial nerve controls the rest of the EOM (not LR or SO)?

A

CN 3

70
Q

PPRF signals what?

A

signals the right abducens ( command from L frontal eye) nucleus to contrac tthe right lateral rectus
signals (via MLF0) the left oculomotor nucleus to contract the left medial rectus

71
Q

involves the rostral intersitital nucleus of the MLF

A

vertical gaze

72
Q

Where do parasympathitic nerve rest?

A

Edinger- Westphal nucleus of CN III which projects to ciliary ganglion

73
Q

Sympathtic nerves are preganglionics; where is this?

A

lateral horn of 1st thoracic segment

synapse on postganglionic in superior cervical

74
Q

Sympathtic dilates pupil; what contracts?

A

radial fibers & contracts superior tarsal muscle (raises eyelid)

75
Q

What pupils do not respond to light but accomodate?

A

Argyll-Roberson pupil

76
Q

Horner’s syndrome

A

lesion in sympathetic path causes ipsilateral contricted pupil, eyelid droop, flushing, loss of sweating

77
Q

PArasympathetic-Syphilis

A

encephalitis
blocks pupillary light reflex
loss of inhibtition results in contricted pupil

78
Q

Assessment of comatose patient

A
  1. doll eyes- head rotation causes eyes to remain fixed, often a CVA affectign brianstem
  2. Blown pupils- mydriasis- trauma or stroke may cause pupils that are fixed and dilated unilaterally or bilaterally. compression of CN III and brainstem. recreational drug use causes temporary pupillary dilation.

physio (14 decks)

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