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physiology 3 > physiology of vision > Flashcards

physiology of vision Flashcards

(72 cards)

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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
hyperopia
farsighted
26
astigmatism
the cornea is irregular > irregular pattern of vision
27
presbyopia
stiffening of the lens occuring with aging | increased difficulty with near vision
28
stereopsis
depth perception | ability to judge distance to objects
29
stereoscopic vision
requires overlapping visual fields with allows each eye to look at the same object from different angles eyes more converged = closer object
30
the near response
close range adjustment - requires 3 precesses - convergences of eyes - constriction of pupil - accommodation of lens
31
3 processes of the near response
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
opoosite of the near response
startle response
33
photoreceptors
photoreceptors - rods and cones | cones densely packed at fovea - centre of macula lutea
34
fovea centralis
back of the retina centre of the macula lutea highest density of colour receptors
35
types of cones
3 for 3 colours
36
retinal pathway
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
rods
100 million per retina presence of photons, regardless of wavelength very sensitive and effective in dim light
38
cones
3 million per retina blue, green and red contain pigments sensitive to specific wavelengths of light less sensitive, function only in bright light
39
Outersegments
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
rhodopsin
opsin and retinal
41
inner segment
contains organelles, synapses with bipolar cells
42
retinal
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
phototransduction
no light = depolarisation = neurotransmitter release light = hyperpolarisation = stops neurotransmitter release bipolar cells reverse the signal ganglion cells transmit action potentials due to light
44
rhodopsin response to no light
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
what activates transducin
opsin
46
what does transducin activate
phosphodiesterase (PDE)
47
what does phosphodiesterase do
breaks down the cells cyclic GMP low cGMP = closed Na+ channels cell hyperpolarises and stops releasing glutamate
48
low cGMP
closed Na+ channels | cell hyperpolarises and stops releasing glutamate
49
how is transretinal converted back to cis low energy form
ATP dependant enzyme RPE65 opsin and cis retnal can bind again
50
heavy light or bleaching
51
dark light
52
2 types of bipolar cells
OFF and on
53
in dark (release of Glu)
Glu depolarises EPSP (OFF bipolar cells) Glu hyperpolarises IPSP (ON bipolar cells) signal is off = glanglion cells are not stimulated
54
in light (absense of Glu)
no glu = OFF bipolar cells are hyperpolarised ON bipolar cells are depolarised signal is on - ganglion cells are stimulated
55
cells generating action potentials
only ganglion cells generate action potentials | - photoreceptors and bipollar cells generate GRADED potentials
56
lateral inhibition
- 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
edges of retina
widely spaced rods | low-res motion detectors
58
fovea
no nueronal convergence - private line to the brain | high resolution colour vision, low sensitivity to dim light
59
1st order nuerones
bipolar cells of retina
60
2nd order nuerons
retinal ganglion cells
61
retinal ganglion axons form the
optic nerve
62
two optic nerves combine to form the
optic chiasm
63
hemidecussation
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
chiasm splits to form
optic tracts
65
optic tracts
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
3rd order neurons
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
optic nerve fibres projecting to the midbrain
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
optic nerve lesion
ipsilateral - same side - blind eye
69
chiasmatic lesion (pituitary tumours)
lateral half of both eyes gone
70
optic tract lesion
opposite half of visual field gone
71
visual projection processing
- 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
subdivisioon of visual cortex to process visual projection
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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