lecture 15- visual system sensory III Flashcards

1
Q

Optic disk (blind spot)

A

area where optic nerve and blood vessels leave the eye

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2
Q

lens

A

bends light to focus it on the retina

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3
Q

Zonules

A

attach lens to ciliary muscle

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4
Q

pupil

A

changes amount of light entering the eye

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5
Q

retina

A

layer that contains photoreceptors

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6
Q

sclera

A

is connective tissue

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7
Q

how does light enter the eye

A

the cornea and lens focus light rays onto the retina

specialized cells in the retina (photoreceptors) transduce light energy into an electrical signal

a network of neurons collect electrical signals to be transmitted along the optic nerve to the brain

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8
Q

how is light refracted when it enters the eye?

A

refracted twice
2/3 cornea (large difference in refractive index)
1/3 by lens (large curvature)

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9
Q

accomodation

A

the lens can change its shape to focus onto the retina
(due to contraction and relaxation of the ciliary muscle

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10
Q

ciliary muscle

A

a right of smooth muscle surrounding the lens

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11
Q

presbyopia

A

loss of accommodation due to loss of elasticity

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12
Q

what happens when ciliary muscle is relaxed

A

the lens is flattened
–> more distant objects are focused on the retina

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13
Q

when ciliary muscle contracts

A

the lens is rounded
–> closer objects are focused on the retina

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14
Q

concave lens

A

scatters light rays (diverges)

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15
Q

convex lens

A

light rays diverge

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16
Q

Light from center of field of view is focused on the

17
Q

area of most acute vision and center of visual field

A

fovea and macula

18
Q

does the fovea have neurons or blood vessels?

19
Q

Rods and cones

A

sensory cells (photoreceptors)
- transduce light energy into electrical signal
- only produce graded potentials

20
Q

Bipolar cells, amacrine cells, horizontal cells

A
  • connect sensory cells to transmitting cells, process and integrate information, converge signals from several photoreceptors
21
Q

Ganglion cells

A

transmitting cells (output to CNS)
- carry information via the optic nerve to the brain
- produce action potentials

22
Q

info from —- rods and cones converges on —– ganglion cells

A

100 million rods and cones
1 million ganglion cells

23
Q

the size of the receptive field depends on…

A

the location on the retina

24
Q

compare ganglion cell receptive fields in the periphery vs in the fovea

A

ganglion cells in the periphery have large receptive fields

ganglion cells in the fovea have very small receptive fields

25
Rods are responsible for
low light/night vision
26
rhodopsin
is a photopigment that is the signal transducer
27
Cones are responsible for
sharp vision and colour vision
28
3 types of cones
each has a different photopigment (related to rhodopsin) and responds to specific colour (red, blue, green)
29
what does light do to rod and cone cells?
it hyperpolarizes them
30
What is rhodopsin? 2 components
opsin + retinal opsin is the GPCR retinal is the visual pigment
31
when opsin and retinal are tightly bound, rhodopsin is
inactive
32
disks are the location of ---- in rods
signal transduction
33
rods and cones transduce
light photons into electrical currents
34
rods and cones project to
bipolar cells
35
bipolar cells synapse with
ganglion cells
36
ganglion cell axons from the
optic nerve and project to the CNS
37
Phototransduction in rods (in darkness) 7 steps
1. retinal and opsin are bound - rhodopsin is inactive 2. cGMP levels inside the cell are high 3. CNG channels are open 4. rod cell is depolarized (-40mV) 5. V-gated Ca2+ channels are open 6. Ca2+ goes into the cell 7. NT (glutamate) is released
38
phototransduction in rods (in the presence of light) 9 steps
-retinal phtotoisomerizes (11-cis --> trans) causes a conformation change in the intracellular C-terminus of rhodopsin 1. rhosopsin is activated (retinal is released) 2. activates associated G protein: transducin 3. transducin activates phosphodiesterase 4. phosphodiesterase breaks down cGMP 5. decreased [cGMP] --> CNG channels close 6. cell hyperpolarizes 7. voltage gated Ca2+ channels close (less Ca2+ into cell) 8. Decreased NT (glutamate release) 9. adjacent bipolar cell and ganglion cell are excited