Detection of Detection of Environmental Conditions Environmental Conditions

in Mammalsin Mammals

Sight -- Structures and Sight -- Structures and Functions of the EyeFunctions of the Eye

Special TermsSpecial Terms

Stimulus: change in internal

and external environments

to living organisms

Response : observable action to a

stimulus

Irritability: ability to respond to

stimuli

Receptor: specialized sensory cell

which can receive stimuli

and set up nerve impulses

to the brainEffector: organ that responds to a

stimulus ( muscle or gland )

stimulus

receptor central

nervous system

effector

response

EYESEYES

Detect Detect lightlight and provide and provide a sense of sighta sense of sight

Consist of an Consist of an eyeballeyeball which is positioned in which is positioned in the the orbit of the skullorbit of the skull

Slide View of the Human EyeSlide View of the Human Eyeball in the Orbitball in the Orbit

eye muscle

orbit optic nerve

lens

Lower eyelid

iris

eyeball

conjunctiva

bone

upper eyelid

Tear glandTear gland: It secretes tears which :: It secretes tears which : wash away foreign particleswash away foreign particles contain lyzozyme which can kill contain lyzozyme which can kill

bacteriabacteria moisten the surface of eyeballmoisten the surface of eyeball

EyelidsEyelids protect the eye from foreign particlesprotect the eye from foreign particles

EyelashesEyelashes protect the eye from dustprotect the eye from dust

Slide View of the Human EyeSlide View of the Human Eyeball in the Orbitball in the Orbit

Internal Structure of the HuInternal Structure of the Human Eyeball man Eyeball ( Horizontal Section )( Horizontal Section )

eye musclesclerachoroid

retina

yellow spot

vitreous humour

optic nerveblood vessels

aqueous humour

conjunctiva

pupil

corneairis

suspensory ligament

ciliary body

blind spot

lens

Eye WallEye Wall (3 (3 layerslayers))

1. Sclera

• Protects the eyeball

• Maintains the shape of the eyeball

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

2. Choroid• Contains many

nerves and blood vessels

• Blood vessels supply oxygen and nutrients to the eye

• Pigment absorbs and reduces reflection of light within the eye

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

2. Retina• Light receptors

here detect light rays from the object and set up nerve impulses

CorneaCornea TransparentTransparent Allows light to Allows light to

enter the eyeenter the eye

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

PupilPupil Hole at irisHole at iris Allows the light to Allows the light to

enter the eyeenter the eye

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

IrisIris Regulates the size of the Regulates the size of the

pupil which in turns pupil which in turns control the amount of light control the amount of light entering the eyeentering the eye

LensLens Transparent Transparent

convex structure convex structure which is elasticwhich is elastic

Refracts and Refracts and focuses light focuses light rays onto the rays onto the retinaretina

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Suspensory Suspensory LigamentsLigaments

Hold lens into Hold lens into positionposition

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Ciliary BodyCiliary Body Adjusts the Adjusts the

shape of the shape of the lenslens

Anterior ChamberAnterior Chamber Filled with watery Filled with watery

fluidfluid Helps in refracting Helps in refracting

light rays onto the light rays onto the retinaretina

Maintains the shape Maintains the shape of the eyeballof the eyeball

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Posterior ChamberPosterior Chamber Filled with jelly-Filled with jelly-

like fluidlike fluid

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Optic NerveOptic Nerve Carries nerve Carries nerve

impulses from impulses from the eye to the the eye to the brainbrain

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Yellow SpotYellow Spot A small area in the centre of A small area in the centre of

the retinathe retina Contains cones onlyContains cones only Responsible for acute visionResponsible for acute vision

Internal Structure ofInternal Structure ofthe Human Eyeballthe Human Eyeball

Blind SpotBlind Spot A point on retina where the A point on retina where the

optic nerve leaves the eyeballoptic nerve leaves the eyeball No light sensitive cells ==> No light sensitive cells ==>

cannot detect imagecannot detect image