Vision Physiology

8/13/2019 Vision Physiology

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PENGLIHATAN

(VISION)


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Objectives1. Fungsi komponen utama mata

2. Mekanisme refleks pupil

3. Mekanisme refraksi4. Proses Akomodasi

. Fotoreseptor

!. Fototransduksi dan inisiasi potensial aksi di jalur pengli"atan

#. Adaptasi gelap dan terang

$. Pengli"atan %arna&. Pengola"an informasi pengli"atan

1'. (truktur lain di sekitar mata )associated structures* dan fungsin+a


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(tructure of t"e ,+eball


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(tructure of t"e ,+eball

Figure 1.$a


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Mekanisme refleks pupilO -ris t"e colored part of t"e e+e

O Pupil / central opening of t"e iris

O 0egulates t"e amount of lig"t enteringt"e e+e during

O lose vision and brig"t lig"t / pupils constrict

O istant vision and dim lig"t / pupils dilate

O "anges in emotional state / pupils dilate%"en t"e subject matter is appealing orreuires problemsolving skills


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Pupil ilation and onstriction

Figure 1.&


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Proses Akomodasi

The ability to adjust the strength of the lens

Regulated by the ciliary muscle

Ciliary muscle is circular ring of smooth muscle

attached to the lens by suspensory ligament ormal eye !

m" ciliary rela#$ suspensory lig" is pulled$ lens is flat for far

vision

m" ciliary contract$ slackening the tension in suspensorylig$ lens is more conve# and stonger for near vision

The ciliary muscle is controlled by the autonomic

nervous sytem$ sympathetic rela#ation$5parasympathetic contraction5


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(ensor+ 6unic 0etina

A delicate t%ola+ered membrane

Pigmented la+er / t"e outer la+er t"at absorbslig"t and prevents its scattering

7eural la+er8 %"ic" contains

P"otoreceptors t"at transduce lig"t energ+ 9ipolar cells and ganglion cells

Amacrine and "ori:ontal cells

Fotoreseptor


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(ensor+ 6unic 0etina

Figure 1.1'a


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;anglion cell a


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e e na ang on e s an eOptic isc

Figure 1.1'b


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0ods

0espond to dim lig"t

Are used for perip"eral vision

ones

0espond to brig"t lig"t

>ave "ig"acuit+ color vision

Are found in t"e macula lutea

Are concentrated in t"e fovea centralis

6"e 0etina

P"otoreceptors


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P"otoreception / process b+ %"ic" t"ee+e detects lig"t energ+

0ods and cones contain visual pigments)p"otopigments*

Arranged in a stack of disklike infoldings oft"e plasma membrane t"at c"ange s"ape

as t"e+ absorb lig"t P"otopigments of rods r"odopsin )opsin

? retinen@retinal*

P"otoreceptionFunctional Anatom+ of P"otoreceptors


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Figure 1.1&

P"otoreceptionFunctional Anatom+ of P"otoreceptors


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P"ototransduction

=ig"t energ+ splits r"odopsin into alltransretinal8 releasing activated opsin

6"e freed opsin activates t"e ; proteintransducin

6ransducin catal+:es activation ofp"osp"odiesterase )P,*

P, "+drol+:es c;MP to ;MP and releases it

from sodium c"annels it"out bound c;MP8 sodium c"annels close8

t"e membrane "+perpolari:es8 andneurotransmitter cannot be released


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P"ototransduction

Figure 1.22


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No light/dark

Concentration cGMP

Na+channels open in outer segmen

Membran depolarization

Spread to the terminal synaptic

Ca+ channels open

!elease neurotransmitter ""inhibitory neurotransmitter#

$ipolar cells inhibited

No action potential in ganglion cell

No action potential propagation to %isual corte&

'i ht


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'ight

(cti%ation o) )otopigment "rod and cone#

(cti%ation o) transducin "G protein#

cGMPNa+ channel closure

Membran hyperpolarization "receptor potential#

Spread to the terminal synaps

Closure ca+ channels

!elease inhibitory neurotrasnmitter

$ipolar cell uninhibited "or in e))ect* e&cited#

Graded potential change in bipolar cell

(ction potential in ganglion cell

isual corte& in the occipital lobe o) the brain

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Vision Physiology