chapter 14 human eye

8/8/2019 Chapter 14 Human Eye

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Chapter

The Human

14

Eye

Learning Objectives

. Describe the gross structure of the eye as seen in frontview and in horizontal section

. State the principalfunctions ofcomponent pafts o{ theeye in producing a focused image of near and dislantobjecls on the relina

. Describe the pupil reflex in response to bright and dim

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Eye magic

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The Eye

. One of the most

important receptors.

. Provides us on

information on

dimensions, coloursand distance of

objects in ourenvironment.

External structure of the eye



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Functions

) Help protect the eyefrom dust particles

Functions

(3) Conjunctiva

)Transparentepithelium

)Covering theof the eyeball

)Secretes mucus to

lubricate, clean andmaintain moisture

)Continuous with theskin of eyelids

Function

(4) Sclera

)Tough

)White, Opaque

)Non-elastic layeroutside the eyeball

)Protects the eyeballfrom mechanicaldamage.

F u nction

(5) Cornea

)Transpa

>Continuous withsclera

)Refracts light rays

into the eye

Function

(6) lris --lfrlj,.tM@



Functions

(7) Pupil

) Round hole at th€i

centre of the iris

through which lightenters-



Vertical Section of The Human_Eye i vertical section of The Human Eye l,..,.,

I Verticalsectlon ofThe Homan Eye

I vertical Sectior of The Human EyeI

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r Verticalssction ofThe Human Eye

1 vertical Section ofThe Human Eye



Photoreceptors

. Cones- enable us to see colours in brightlig ht.

. Red, blue and green cones

. Each cone absorbs light of differentwavelengths.

. Do not work well in dim light.

Photoreceptors

' Rods and Cones are stimulated by the

light of the image, and convert the light

energy ) electrical energy

. Electrical energy ) travels in the form ofan impulse ) along the optic nerve ) to

the brain.. Brain ) de-codes the impulse to produce

the sensation of sight.

Photoreceptors

. Rods -enable us to see in dim light

. See only in black and white

. Contain visual purple (Vitamin A)

. Bleached by light

. Re-formed in the dark

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Chapter 14 The Human EyeHow Do We See?

How Do We See?

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How Do We See?

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a4ueous hunour onto L\c lens

Tne oage fom.d is Thc inags on $c rcrina. invcrt€d $nnu1a1es cither lne rods or

rhc cones, d@cndinr on ih!

PupilReflex

7

Pupil Reflex

ln Dim Lioht(1) Lrqht sensruve @lls n lhe

Frin: ddF.l ihF lidhrinlensity.

(2) lmpulse are sent alonq theoptic newe ro lhe bran

(3) Brain retums the impulsealong a motor neumne to theEdialmuscles ol lhe ins

(4) Radial iis muscles contracr,cirular iris muscles relax

(5) Diameter oi lne pupilinseases allowing more light



ln Dim light

ln Bright light

Action gf lris in.Brignt Light

PupilReflexR.di.lln bnghtlight muscres Ellt

(1) liohl sonsliive cells intherehna dete.l the I'ohtinlensily

(2) lmpurse are sentalons theoptic nerve lo lhe brain

(3) Arain retums the impulsealono a molor nelrone lo lheradblmuscles of the ins

(4) Radialins muscleE relar,cirular ins muscles conrrecl

(5) Oismeler of lhe pupildecre€ses allowing less light

l4s in,E Light



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Accommodation. The ability of the lens to change and

focus on objects at different distances iscalled accommodation.

. This depends on:-

('1) Elasticity of the lens

(2) Ciliary muscles which alter the shape ofthe lens.

(3) Suspensory ligaments

Ma6ha Cav€ndirh

Chapter 14 The Human EyeAction of Iris in Dim Liqht



Accommodation

When viewino near When viewinq distantobiects obiects

(1) Ciliary muscles (1) Ciliary muscles

contract relax

(2) Suspensory (2) Suspensoryligamentsrelax ligamentscontract

(3) Lens thicker, more (3) Lens thinner, less

curved r curyed

Distant objectHow

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Nearby objectiB Ma6hall (alrendi'h

Chapter 14 The Human EyeHow Eyes Focus on Near Objects

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chapter 14 human eye

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