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ANP1106 > Vision > Flashcards

Vision Flashcards

1
Q

What are the 5 main accessory eye structures?

A

Eyebrows
Eyelids
Conjunctiva
Lacrimal apparatus
Extrinsic eye muscles

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2
Q

What are the 3 parts of the conjunctiva?

A

Palpebral (eyelid lining)
Bulbar (membrane that covers the whites of eye)
Conjunctival sac (space between them, Where does a contact lens sit)

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3
Q

How many extrinsic eye muscles exist? What are their 3 functions? Which cranial nerves control them?

A

6 (per eye)
Track moving objects
Maintain eyeball shape
Stabilize orbit position
-CN III (Oculomotor)
-CN IV (Trochlear)
-CN VI (Abducens)

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4
Q

What are the 3 wall layers of the eyeball?

A

-Fibrous (sclera/cornea)
-Vascular (choroid/ciliary body/iris)
Inner (retina)

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5
Q

What fluid fills the internal cavity?

A

Humors

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6
Q

Where is the outer pigmented layer located?

A

single-cell-thick lining next to choroid, extending to cover ciliary body/iris

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7
Q

What are the 3 key functions of outer pigmented layer?

A

-Absorbs light and prevent scattering of light
-Stores vitamin A
- Phagocytoses photoreceptor debris

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8
Q

What are the 3 main neuron types in the neural layer of retina?

A

-Photoreceptors (rods/cones)
-Bipolar cells
-Ganglion cells

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9
Q

Where do ganglion cell axons exit the eye?

A

Optic disc (as optic nerve)

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10
Q

What is the signal pathway through these neurons?

A

Light → Photoreceptors → Bipolar cells → Ganglion cells (APs generated)

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11
Q

Why is the optic disc called the “blind spot”?

A

Lacks photoreceptors → no light detection

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12
Q

What type of vision are rods specialized for?

A

Dim light and peripheral vision

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13
Q

What type of vision are cones specialized for?

A

Bright light and color vision

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14
Q

Why are photoreceptors considered “modified neurons”?

A

They transform light energy into neural signals but have epithelial-like structure> resembling upside down epithelial cells.

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15
Q

What is the function of the outer segment?

A

Light receiving region (contains visual pigments in stacked membranes) that changes shape as they absorbs light

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16
Q

What is the function of inner segment?

A

each joins cell body
▪ Inner segment is connected via
cilium to outer segment and to cell
body via outer fiber

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17
Q

What are the 3 stages of rhodopsin activity?

A
  • Pigment synthesis (opsin + retinal)
  • Pigment bleaching (light absorption)
  • Pigment regeneration
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17
Q

What is phototransduction?

A

Conversion of light energy into graded receptor potential

18
Q

What is the visual pigment in rods?

A

Rhodopsin (deep purple pigment)

19
Q

What is retinal?

A

The light-absorbing molecule derived from vitamin A that combines with opsins to form visual

20
Q

What are the two forms of retinal?

A

11-cis-retinal (bent, dark-adapted form)

All-trans-retinal (straight, light-activated form)

21
Q

How does rhodopsin synthesis occur?

A

by combining 11-cis-retinal derived from vitamin A with opsin

22
Q

What happens during pigment bleaching?

A

Light converts retinal shape 11-cis-retinal → all-trans-retinal, Releasing opsin

23
Q

How does pigment regeneration occur?

A

enzymes slowly covert all-trans- retinal to its 11-cis-retinal form in the pigment layer. This then rejoin with opsin to regenerate rhodopsin

24
Photo transduction. What is the light-activated receptor? and what does it do when activated
Contains 11-cis-retinal > which changes shape when absorbs light then activate a gprotein
25
Which G protein does activated rhodopsin trigger?
Transducin (Gₜ) >Binds GTP when activated
26
What enzyme does transducin activate?
* Phosphodiesterase (PDE) * Breaks down cGMP → GMP > causing cGMP levels to drop
27
Signal transmission in Retina (In the dark)
1) cGMP channels opens, allowing cation inflex > photoreceptor depolarization 2) Volatge gated CA2+ opens in synaptic terminal 3) Neutrotransmitters flow 4) Neurotransmitter causes IPSP to occur in bipolar cell, therefore hyperpolarization 5) Hyperpolarization closes CA2+ channels > neurotransmitter release is inhibited 6) NO EPSP occurs 7) No AP
27
What is the second messenger being degraded?
* cGMP * Decrease closes cation channels of cGMP → results in hyperpolarization
28
Signal transmission in Retina (In the light)
1) cGMP-gated ions closes causing cation influx to stop > hyperpolarization 2) Volatge gated Ca2+ close in synaptic terminal 3) no neurotransmitter released 4) Lack of IPSP in bipolar cells > results in depolarization 5) Ca2+ voltages gated channels open > neurotransmitter released 6) EPSP occurs in ganglion cells 7) Action potential propagate a long optic nerve
29
Which retinal cells use graded potentials vs. action potentials?
* Graded potentials: Photoreceptors & bipolar cells * Action potentials: Ganglion cells only
30
How does light affect glutamate release?
* Dark: Photoreceptors release inhibitory glutamate * Light: Hyperpolarization stops glutamate → bipolar cells depolarize
31
What happens during light adaptation?
-Pupils constrict -Rods turn off (bleached) -retinal sensitivity decreases -Cones take over (~5-10 min) -Glare initially from rapid pigment breakdown (both rods and cons are stimulated)
32
What occurs in dark adaptation?
-Pupils dilate -Cones stop functioning -Rhodopsin regenerates or accumulate → rods regain sensitivity (~20-30 min)
33
What happens at the optic chiasm?
* Medial fibers cross → each optic tract carries contralateral visual field * Lateral fibers stay ipsilateral
33
Where do most optic tract fibers synapse?
* Lateral geniculate nucleus (LGN) of thalamus → optic radiations (formed from thalamic neurons) → primary visual cortex
34
What are the alternate optic tract destinations?
- Superior colliculi: Eye movement control - Pretectal nuclei: Pupillary reflexes (melanopsin) - Suprachiasmatic nucleus: Circadian rhythms (melanopsin ganglion cells)
35
How does the eye focus for distant vision?
* Ciliary muscles relax → zonule fibers tighten * Lens flattens (reduced refraction)
36
What 3 adjustments occur for near vision?
Lens accommodation: Changing lens shape to increase refraction Pupil constriction: Parasympathetic response → blocks divergent rays Convergence: Eyes rotate medially
37
How does the eye focus for close vision?
* Parasympathetic input causes Ciliary muscles contract → zonule fibers loosens * Lens bulges
38
What causes myopia? How is it corrected?
* Eyeball too long → focal point in front of retina * Corrected with : Concave lenses diverge light before entry
39
What causes hyperopia? How is it corrected?
* Eyeball too short → focal point behind retina * Corrected with : Convex lenses converge light before entry
40
Trace the visual pathway from retina to cortex:
Photoreceptors → 2. Bipolar cells → 3. Ganglion cells → 4. Optic nerve → 5. Optic chiasm → 6. LGN → 7. Visual cortex

ANP1106 (8 decks)

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