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physiology 3 > physiology of vision > Flashcards

physiology of vision Flashcards

1
Q

4 things needed to see an object

A
  1. iris control
  2. accommodation
  3. phototransduction
  4. visual pathways
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2
Q

iris control

A

amount of light entering the eye must be regulated (too much light will bleach out signals)

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3
Q

accommodation

A

the object’s pattern must fall on the vision receptors

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4
Q

phototransduction

A

energy from waves of photos must be transduced into APs

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5
Q

visual pathways

A

brain must recieve and interpret signals

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6
Q
A
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7
Q

cornea is for

A

protection

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8
Q

iris

A

expands or contracts to let varying amounts of light through

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9
Q

lens

A

can be more curved or flat for focus

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10
Q

retina

A

situated at the back of the eye

photoreceptors and first order neurons which feed into the optic nerve

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11
Q

optic nerve

A

exits the eye via the optic disk

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12
Q

blind spot

A

where the optic nerve leaves the eyeball

is the optic disk

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13
Q

muscles of the eye

A
  1. 6 x extraocular muscle
  2. circular and radial iris sphincters (pupil size)
  3. ciliary muscle (lens shape)
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14
Q

ciliary muscle

A

contraction leads to curvature of the lens

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15
Q

the iris controls the

A

pupil sze

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16
Q

2 iris muscles

A
  • circular iris sphincter muscle

- radial iris dilator muscle

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17
Q

circular ris sphincter muscle

A

constriction
reduces light
under parasympathetic control

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18
Q

radial iris dilator muscle

A

dilation
more light
under sympathetic control

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19
Q

pupillary constriction and dilation occurs when

A
  • when light intensity changes
  • when gaze shifts between distant and nearby objects
  • during arousal
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20
Q

photopupllary reflex

A

pupil constriction in response to light
autonomic reflex arc
1. brighter light signalled to midbrain (pretectal region), connects to the edinger-westphal nucleus, controls both left and right oculomotor nerves
2. excites parasympathetic fibres in oculomotor nerves that travel to ciliary ganglia in both eyes, stimulate pupillary constrictor
3. consensual (both pupils with constrict, even if one is shielded)

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21
Q

pretectal region

A

region of midbrain

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22
Q

accomodating to nearby objects

A

need more round lens
ciliary muscle contracts, suspensory ligaments slacken, and lens takes more convex (rounded) shape
parasympathetic

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23
Q

accomodating to distant objects

A

need fllat lens
ciliary muscle relaxes, suspensory ligaments tighten and lens takes less conves (flatter) shape
sympathetic

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24
Q

myopia

A

near sighted

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25
Q

hyperopia

A

farsighted

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26
Q

astigmatism

A

the cornea is irregular > irregular pattern of vision

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27
Q

presbyopia

A

stiffening of the lens occuring with aging

increased difficulty with near vision

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28
Q

stereopsis

A

depth perception

ability to judge distance to objects

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29
Q

stereoscopic vision

A

requires overlapping visual fields with allows each eye to look at the same object from different angles
eyes more converged = closer object

30
Q

the near response

A

close range adjustment - requires 3 precesses

  • convergences of eyes
  • constriction of pupil
  • accommodation of lens
31
Q

3 processes of the near response

A

convergence of eyes - eyes orient their visual axis toward object
constriction of pupil - blocks peripheral light rays and reduces spherical aberration (blurry edges)
accomodation of lens - ciliary muscle contracts, suspensory ligaments sllacken, and lens is more convex, = near point of vision

32
Q

opoosite of the near response

A

startle response

33
Q

photoreceptors

A

photoreceptors - rods and cones

cones densely packed at fovea - centre of macula lutea

34
Q

fovea centralis

A

back of the retina
centre of the macula lutea
highest density of colour receptors

35
Q

types of cones

A

3 for 3 colours

36
Q

retinal pathway

A

photoreceptors > bipolar cells > ganglion cells > optic nerve
- axons of ganglion cells converge at optic disc (blind spot)
horizontal cells and amacrine cells sharpen/modify the signal

37
Q

rods

A

100 million per retina
presence of photons, regardless of wavelength
very sensitive and effective in dim light

38
Q

cones

A

3 million per retina
blue, green and red
contain pigments sensitive to specific wavelengths of light
less sensitive, function only in bright light

39
Q

Outersegments

A

contains 100s - 1000s of flattened discs
- contain visual pigments - absorb photos - initiate photoreception
made of rhodopsin
retinal is the same in rods and cones, opsins are different

40
Q

rhodopsin

A

opsin and retinal

41
Q

inner segment

A

contains organelles, synapses with bipolar cells

42
Q

retinal

A

vitamin A
has 2 isomers - low and high energy form
only one associated with opsin
when light is absorbed, retinal changes form and no longer associated with opsin

43
Q

phototransduction

A

no light = depolarisation = neurotransmitter release

light = hyperpolarisation = stops neurotransmitter release

bipolar cells reverse the signal

ganglion cells transmit action potentials due to light

44
Q

rhodopsin response to no light

A

cis-retinal binds to opsin ( low energy form)
light energy converts cis to trans- retinal (rhodopsin dissociates)
opsin starts signalling = binds and activates transducin (a G protein)

45
Q

what activates transducin

A

opsin

46
Q

what does transducin activate

A

phosphodiesterase (PDE)

47
Q

what does phosphodiesterase do

A

breaks down the cells cyclic GMP
low cGMP = closed Na+ channels
cell hyperpolarises and stops releasing glutamate

48
Q

low cGMP

A

closed Na+ channels

cell hyperpolarises and stops releasing glutamate

49
Q

how is transretinal converted back to cis low energy form

A

ATP dependant enzyme
RPE65
opsin and cis retnal can bind again

50
Q

heavy light or bleaching

A
51
Q

dark light

A
52
Q

2 types of bipolar cells

A

OFF and on

53
Q

in dark (release of Glu)

A

Glu depolarises EPSP (OFF bipolar cells)
Glu hyperpolarises IPSP (ON bipolar cells)
signal is off = glanglion cells are not stimulated

54
Q

in light (absense of Glu)

A

no glu = OFF bipolar cells are hyperpolarised
ON bipolar cells are depolarised
signal is on - ganglion cells are stimulated

55
Q

cells generating action potentials

A

only ganglion cells generate action potentials

- photoreceptors and bipollar cells generate GRADED potentials

56
Q

lateral inhibition

A
  • horizontal cells - input from photoreceptors and output to photoreceptors and bipolar cells
  • amacrine - input from bipolar, output to ganglion cells, bipolar cells, other amacrine cells
  • sharpens image, defines lines/patterns of light/dark contrast
57
Q

edges of retina

A

widely spaced rods

low-res motion detectors

58
Q

fovea

A

no nueronal convergence - private line to the brain

high resolution colour vision, low sensitivity to dim light

59
Q

1st order nuerones

A

bipolar cells of retina

60
Q

2nd order nuerons

A

retinal ganglion cells

61
Q

retinal ganglion axons form the

A

optic nerve

62
Q

two optic nerves combine to form the

A

optic chiasm

63
Q

hemidecussation

A

half of the fibres cross over to the opposite side of the brain
right cerebral hemisphere sees objects in left visual field because their images fall on the right half of each retina
each side of brain sees what is on side where is has motor control over limbs (everything on your right is seen by the left side of your brain)

64
Q

chiasm splits to form

A

optic tracts

65
Q

optic tracts

A

send axons to thalamus - lateral geniculate nucleus

3rd order neurons arise here and form the optic radiation of fibres in the white matter of the cerebrum

66
Q

3rd order neurons

A

arise at the lateral geniculate nucleus (thalamus)
form the optic radiation of fibres in the white matter of the cerebrum
project to primary visual cortex (occipital lobe) where conscious visual sensation occurs

a few optic nerve fibres project to midbrain and terminate in the superior colliculi and pretectal nuclei

67
Q

optic nerve fibres projecting to the midbrain

A

terminate in the superior colliculi and pretactal nuclei

  • cuperior colliculi controls visual reflexes of extrinsic eye muscles
  • pretectal nuclei are involved in photopupilary and accommodation reflexes
68
Q

optic nerve lesion

A

ipsilateral - same side - blind eye

69
Q

chiasmatic lesion (pituitary tumours)

A

lateral half of both eyes gone

70
Q

optic tract lesion

A

opposite half of visual field gone

71
Q

visual projection processing

A
  • some in the retina
  • more in the lateral geniculate nucleus
  • further in the primary visual cortex (V1) is connected by association tracts to visual association areas
72
Q

subdivisioon of visual cortex to process visual projection

A

V1 - initial conscious perception + retinotopic mapping
V2 - orientation, spatial frequency, size, colour, and shape
V3 - motion characteristics
V4 - recognition of form (capable of memory formation)
V5 - speed and direction of moving visual stimuli
V6 - sharpness of boundaries and visual contours

physiology 3 (7 decks)

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