eye 𐙚

• Examples of stimulus: Eye - bright light, dim light , far object, close object
• Examples of receptor

  Photoreceptor
• Examples of effector

  Light - Circular muscle & Radical muscle Distance - Cillary body
• In bright lighting, circular muscle contracts, radical muscle relaxes, pupil constricts
• In dark lighting, circular muscle relaxes, radical muscle contracts, pupil dilates
• Bright light > constricted pupil
• Dim light > Dilated pupil
• Far object - cillary body relaxes, suspensory ligament will be pulled taut, lens will be thinner and less convex
• Near object, cillary body contracts, suspension y ligament will slacken, lens will be thicker and more convex
• Pupil - a hole in the centre of the iris, allowing light to enter the eye
• Eyelash - Shields the eye from dust particles
• Tear gland - secretes tears to 1. wash away dust particles, 2. keep cornea moist for atmospheric oxygen to dissolve, 3. lubricate the conjunctiva to reduce friction when the eyelids move
• Eyelids- protects the cornea from mechanical damage
• Squinting prevents excessive entry of light
• Blinking spreads tears over the eyes so that dust can be wiped off
• Iris - contains a pigment that gives eye its color
• Iris - consists of circular and radical muscles
• Sclera - tough, white outer covering of the eyeball which is continuous with the cornea , protects eye from mechanical damage
• Conjuctiva - a mucus membrane, covering the sclera and secretes mucus to keep the front of the eyeball moist
• Cornea - a dome-shaped transparent layer that is able to refract light rays into the eye
• internal structure

  
• Choroid - black pigmented middle layer which prevents the internal refraction of light
• Choroid - contains blood vessels that carry oxygen and nutrients to eyeball and remove metabolic waste products from the eyeball
• Retina is the innermost layer of the eye wall
• Retina - contains light-sensitive cells known as photoreceptors ( rods and cones )
• Retina - connected to nerve fibres from the optic nerve
• Fovea - a small yellow depression where images are focused
• Fovea - contains cones but not rods
• Fovea - enables a person to have detailed color vision in bright light
• Blind spot - where the optic nerve leaves the eye
• Blind spot - does not contain photoreceptors, not sensitive to light
• Optic nerve - transmits impulses from the retina to the brain when photoreceptors are stimulated
• Viterous chamber– space behind the lens
• Viterous chamber - filled with viterous humour, a transparent jelly-like substance
• Viterous chamber - maintains the convex shape of the eyeball by keeping it firm and refracts light onto the retina
• Suspensory ligament - attaches the edge of the lens to the cillary body
• Suspensory ligament - causes changes in lens shape by transmitting force from the cillary muscle
• Cillary muscle - control the curvature and thickness of lens
• Lens - transparent, circular and biconvex structure
• Lens - shape or thickness can be changed in order to refract light onto the retina