Lec 15 Flashcards by Mahan Tavakolian

Light pathway

1- cornea
2- aqueous humor
3- pupil
4- lens
5- vitreous fluid
6- retina (fovea)

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Optic nerve

Primary neurons axon

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Optic disk

Anatomical blind spot
No photoreceptor

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Light is focused by

Light is bend by
Cornea (2/3)
Lens (1/3) changeable shape

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Photoreceptors

Specialized cell in retina that transduce light energy to electrical signal

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Eye lens is

Convex
Converging light rays on focal point
Focal point=fovea on retina

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Light must be focused on ——— for clear vision

Retina
How?
Lens change its shape by accommodation

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Accommodation is due to

Due to Contraction and relaxation of ciliary muscles

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Ciliary muscle

Ring of smooth muscle surrounding the lens

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Ciliary muscle is connected to lens by

Ligaments

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When ciliary muscle is relaxed,

Lens is flattened—more distant objects can be seen

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When ciliary muscle is contracted m,

Lens is rounded—closer objects can be seen

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Presbyopia

Loss of accommodation due to loss of lens elasticity

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Macula

Super-focused region
In the middle is fovea

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Fovea

Free of neurons and blood vessels

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Cells in order from vitreous space

1- retina ganglion cell—neurons
2- amacrine cell
3- bipolar neurons—intermediary
4- horizontal cell
5- cone/rods—photoreceptors
6- retina pigment epithelium—melanin absorbs excess light

Rods and cons

Sensory cell/photoreceptors
Light energy—>Electrical energy
Produce Graded potential(release neurotransmitters)

Rod is dim light
Con is bright light

Bipolar-amacrine-horizontal cells

-Connect sensory cells to neurons
-Converge signal from several receptors

Ganglion cells

-Transmitting cells (output to CNS)
-Carry information via optic nerve to brain
-produce AP

Periphery of retina vs center of retina

Periphery:
— many bipolar cells are synapses with one ganglion cell (bigger receptive field)

Center of fovea:
— one ganglion cell is synapsing with one bipolar cell (very small receptive field)

Old disks at tip of cons/rods are

Phagocytized by pigment epithelial cells

Outer segment of photoreceptors

Light transduction takes place using visual disks

Inner segment photoreceptors

Location of major receptors and metabolic operations

Synaptic terminal

Synapses with bipolar cells

Disks are activated by ———

Light

Disks have ——— which are ——— that are activated by ———

1- opsin in rhodopsin 2- GPCR 3- light

Rhodopsin

=Opsin + Retinal Photopigment that is signal transducer

Cones are responsible for

Sharp vision Color vison

3 different types of cones

-Each has different photopigment -Respond to specific color (red/blue/green)

Retinal

11-cis retinal Visual pigment Derivative of vitamin A

When opsin and retinal are tightly bound, rhodopsin is

Inactive

11-cis retinal

Inactive—kinked—required Change to active by light All-trans retinal is active

G protein in rods

Gtransducin

Phototransduction in Rods in darkeness

1-Retinal(11-cis) and opsin is bound 2-Rhodopsin is inactive 3-PDE is inactive 4-cGMP level inside the cell are high 5-CNG channels are open (Ca will move in) 6-Rod cells are depolarized 7-Voltage-gated Ca channel are open 8-Ca into cell 9-Neurotransmitter=glutamate is released

Phototransduction in Rods in light

0-Retinal photoisomerizes 0-11-cis to trans 0-cause conformational change in rhodopsin 1-Rhodopsin is activated(opsin released) 2-Activate Gtransducin 3-Active phosphodiesterase (PDE) 4-PDE break down cGMP 5-Decrease in [cGMP] will close CNG channels 6-Cell hyperpolarize (k link channel) 7-V-gated Ca channels close 8-Decrease NT(glutamate) release 9-Excite adjacent bipolar cell by removing inhibition 10-bipolar cell excite 11-receptor potential 12-bipolar cells release glutamate 13- now excitatory on ganglion cell 14- AP in ganglion cell

From optic nerve to brain

1- optic nerve 2- optic chiasm **cross happens** 3- optic tract 4- lateral body 5- thalamus 6- visual cortex on occipital lobe

Glutamate is inhibory/excitatory??

Inhibitory