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vision Flashcards

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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
Deuteranomaly
green cone peak sensitivity is shifted toward red (5% males)
26
protanomaly
red cone peak shifted towards green (1% males)
27
Signals (except GC) are propagated by
electrotonic conduction
28
photoreceptors synapse on
bipolar cells and HC cells
29
Bipolar cells synapse on
ganglion cells with axons and 'true' action potentials | amacrine cells
30
retinal sensitivity increases 10,000 at 40 min dark
rods
31
dark adaption 4x faster; saturation
cones
32
what phosphorylates rhodopsin producing and adaption mechanism for regulating light sensitivity (light adaption)?
rhodopsin kinase
33
lateral inhibition enhances what?
contrast
34
horizantal cells main mediator of lateral inhibition
pr synapse on adjacent BCs | inhibition by GABA
35
prevents lateral spread of light excitation on retina
horizantal cells
36
creates on/off organization; typical feature of sensory systems
horizontal cells
37
lateral inhibition: color opponency
horizantal cells release of GABA on adjacent PR terminals ( opens Cl- channels) and opposes color signal
38
off-center BCs via..
typical glutamate receptors | hyperpolarize in light
39
On-center BCs express..
mGluR6 which maintains TRMP1 in a closed state
40
What relieves the glutamate inhibition and opens the TRPM1 channels
light
41
optic nerves are always
ipsilateral
42
once it reaches optic chiasm, optic nerve is refferred to as..
optic tract
43
What are the two pathways that optic radiation LGN axons project to?
parietal and temporal
44
superior visual field goes to
inferior retina--> inferior visual cortex | and vis versa
45
Functions of LGN
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
2 innermost layers of the LGN
M-cells
47
4 outermost layers of LGN
P-cell
48
What is adjacent tot the primary visual cortex (area 17)?
calcarine fissure
49
Area 18 is responsible for higher order visual informaiton processing; what is this area called?
secondary visual cortex
50
left visual field projects to...
right primary visual cortex
51
Ocular Dominance Column
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
M path superior termination
area 18/ POT for 3d position, shape, and motion
53
P path inferior termination
temporal lobe for fine detail and color information
54
What cells respond to specific orientation or direction and where does it occur?
simple cells | layer IV
55
Distal to layer VI, some neurons sensitive only to directional movement across the image
complex cells
56
most distal cortical layers, some neurons only respond to specific line lengths, angles and velocities
hypercomplex cells
57
specific neuronal polls are sensitive to specific image features
generalization
58
What fibers from GLN convey color signals and fine details?
P fibers
59
P fibers form LGN project where?
to sublayers a and cbeta in layer IV
60
voluntary fixation area (frontal eye field)
bilateral premotor cortex for voluntary control EOM
61
involuntary fixation area (area 18)
bilateral to automatically 'lock' eyes on target
62
What are the three types of eye movement?
1. continuous tremor 2. slow drift 3. flicking movement
63
What type of eye movement is lost with lesion to the superiror colliculus?
flicking movement
64
What is used to test for 'pursuit movement'?
opticokinetic drum
65
Saccades are also referred to as ...
anticipatory jumps
66
What are the 6 EOMs and the pairs?
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
What cranial nerve is the lateral rectus controlled by?
6
68
What cranial nerve is the superior oblique controlled by?
4
69
What cranial nerve controls the rest of the EOM (not LR or SO)?
CN 3
70
PPRF signals what?
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
involves the rostral intersitital nucleus of the MLF
vertical gaze
72
Where do parasympathitic nerve rest?
Edinger- Westphal nucleus of CN III which projects to ciliary ganglion
73
Sympathtic nerves are preganglionics; where is this?
lateral horn of 1st thoracic segment | synapse on postganglionic in superior cervical
74
Sympathtic dilates pupil; what contracts?
radial fibers & contracts superior tarsal muscle (raises eyelid)
75
What pupils do not respond to light but accomodate?
Argyll-Roberson pupil
76
Horner's syndrome
lesion in sympathetic path causes ipsilateral contricted pupil, eyelid droop, flushing, loss of sweating
77
PArasympathetic-Syphilis
encephalitis blocks pupillary light reflex loss of inhibtition results in contricted pupil
78
Assessment of comatose patient
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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