vision physiology
TRANSCRIPT
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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