Detection of Environmental Conditions in Mammals Sight -- Structures and Functions of the Eye

Special 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 brain Effector: organ that responds to a stimulus ( muscle or gland )

stimulus receptor central nervous system effector response

EYES  Detect light and provide a sense of sight  Consist of an eyeball which is positioned in the orbit of the skull

Slide View of the Human Eyeball in the Orbit eye muscle orbitoptic nerve lens Lower eyelid iris eyeball conjunctiva bone upper eyelid

 Tear gland: It secretes tears which :  wash away foreign particles  contain lyzozyme which can kill bacteria  moisten the surface of eyeball  Eyelids  protect the eye from foreign particles  Eyelashes  protect the eye from dust Slide View of the Human Eyeball in the Orbit

Internal Structure of the Human Eyeball ( Horizontal Section ) eye muscle sclera choroid retina yellow spot vitreous humour optic nerve blood vessels aqueous humour conjunctiva pupil cornea iris suspensory ligament ciliary body blind spot lens

 Eye Wall (3 layers) 1. Sclera Protects the eyeball Maintains the shape of the eyeball Internal Structure of the 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 of the Human Eyeball

2.Retina Light receptors here detect light rays from the object and set up nerve impulses

 Cornea n Transparent n Allows light to enter the eye Internal Structure of the Human Eyeball

 Pupil n Hole at iris n Allows the light to enter the eye Internal Structure of the Human Eyeball  Iris n Regulates the size of the pupil which in turns control the amount of light entering the eye

 Lens n Transparent convex structure which is elastic n Refracts and focuses light rays onto the retina Internal Structure of the Human Eyeball

 Suspensory Ligaments n Hold lens into position Internal Structure of the Human Eyeball  Ciliary Body n Adjusts the shape of the lens

 Anterior Chamber n Filled with watery fluid  Helps in refracting light rays onto the retina  Maintains the shape of the eyeball Internal Structure of the Human Eyeball

 Posterior Chamber n Filled with jelly-like fluid Internal Structure of the Human Eyeball

 Optic Nerve n Carries nerve impulses from the eye to the brain Internal Structure of the Human Eyeball

 Yellow Spot n A small area in the centre of the retina n Contains cones only n Responsible for acute vision

Internal Structure of the Human Eyeball  Blind Spot n A point on retina where the optic nerve leaves the eyeball n No light sensitive cells ==> cannot detect image