group+1 sensory+receptor vision

8/3/2019 Group+1 Sensory+Receptor Vision

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SENSORY VISION

(EYES)

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References???


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MOHAMMAD HAFIDZUDDIN BIN ISHAK

145364 NURFITRI LIYANA BINTI SHAMSHUDIN

151470 ROHANA BINTI ISHAK

151850 MOHAMAD AZRI BIN AHMAD

151914 SITI NURUL AMIRAH BINTI MD DUJALI152116

NURUL AINI BINTI ISMAIL152234


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Specialized cells that begin the process by which

the light rays are converted to nerve impulses.

Located in the distinct layers of retinal neurons.

It has outer and inner segment.

Outer segment composed of layers of

membranes, disc.


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Layers of membranes hold chemical substances

that respond to light.

Inner segment contain nucleus,

mitochondria, others and synapticterminal that connects.


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Types

Rods

Discs membrane areintracellular structure.

Contain about 120million in each retina.

Cones

Light sensitive discs areformed from in-folding of

the surface plasmamembrane. Contain about 6

million in each retina.


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Allow to see in dim light, example : moonlight.

It do not provide color vision.

In dim light can only see black, white and all shades

of grey in between.

Person who loses rod vision having difficulty seeing

in dim light, should not drive at night.


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Stimulates by brighter lights and produce colorvision.

3 types :1) Blue conessensitive to blue light

2) Green conessensitive to green light

3) Red conessensitive to red light

Color vision results from the stimulation of various

combinations of those blue, green and red cones.


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Two layerschoroid and pigment epithelium

Function as to absorb light that has bypassed the

photoreceptors.

To prevent its reflection and scattering back through

the photoreceptors.


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4 unique photo pigments.

Rhodopsin in rods and one in each 3 different types

of cones.

A molecule known as opsin found in each photo

pigments and differs to 4 photopigments.


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Opsin bind together with chromophore and caused

the absorption of light most effectively at a specific

part of visible spectrum.

Ex: red cones, blue cones and etc.


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Involves two condition-darkness (dark current) and light

Dark current: Na+ flows into photoreceptor outer

segments through Na+ channels, held open by cyclicGMP (guanosine monophosphate)

inflow of Na+ triggers continual release of

neurotransmitter (glutamate) from synaptic terminals

Glutamate inhibits (hyperpolarizes) bipolar cells

synapting with rods


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When light strikes the retina & cis-retinalundergoes isomerization, the Na+ channels close

Na+ flow decreases

Inside of the rod becomes more negative(hyperpolarization)

Release of glutamate decreases

Dim lights cause small and brief hyperpolarization,

partially turn off glutamate release Brighter lights enlicit larger and more

hyperpolarizations; completely shut downneurotransmitter release


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Two enzymes regulate closing and opening of Na+

channels in the outer segment.

Transducin (light) and recoverin (darkness) Transducin activates enzyme PDE

(phosphodiesterase), which breaks down cyclic

GMP; closes Na+ channels resulting in

hyperpolarization of rods & decrease in glutamate

Recoverin activates guanylate cyclase, enzyme that

stimulates the synthesis of cyclic GMP. Cyclic GMP

increases, Na+ channels open , inflow of Na+triggers increased release of glutamate


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Neural layer of theretina

Features ofvisual input

areenhanced

Features ofvisual inputdiscarded

Converge

diverge

a large no.of

postsynapticneurons

dominantSmaller no ofpostsynaptic

neurons

Input from several cell divided to:


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Receptor potential arise in outer segment of rods and cone

Spread through inner segment to synaptic terminal

Neurotransmitter molecules release by rods and cones induce local gradedpotential in both bipolar and horizontal cell

6-600 rod synapse with asingle bipolar

A cone more often synapsewith a single bipolar

increase light intensity of rodvision but slightly blurs

Stimulation of rods by light

excites bipolar cell

Cone bipolar excites when a

light is turn on

Less sensitive but have sharpimage


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Horizontalcells transmit

excited

to

Bipolar cell inthe area lateralto excited rod

and cone

Lateral inhibitorenhanced contrast in

the visual scene

Assist in thedifferentiation of

various color

Inhibitorysignal

Horizontal cells

Bipolar cell Synapse withganglia cells and

transmitsinformation to

themSignal a change inthe level of

illumination of retina

Amacrine cells

Ganglion cellbecome

depolarized andiniatiate nerve

impulse

Amacrine cells


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BRAIN PATHWAY

AND VISUAL

FIELDS


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Lateral

geniculatenucleus ofthalamus

The left half of the visual cortexin the occipital lobe receivesinformation from the right half ofthe visual field of both eyes

(green).The right half of the cortexreceives information from the lefthalf of the visual field of botheyes (orange)

Lateral geniculate nucleus

first stop in the mammalianbrain for information in thevisual pathway.

Optic radiation

Separate information receivedfrom the eyes


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Binocular overlapping area seenby both eyes at the same time.

Achieve in part by routing axonsfrom one eye together with axonsfrom the other eye to synapse in thesame layers of the lateral geniculatenucleus.

Depending on the placement of theeyes in the skull,both the extend ofvisual field and the amount ofbinocular overlap can vary.

group+1 sensory+receptor vision

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