the eye

• label:

  A) lens

  B) pupil

  C) iris

  D) cornea

  E) blind spot

  F) optic nerve

  G) sclera (outer)

  H) choroid (middle)

  I) retina (inner)

  
• receptor cells detect light
• blind spot has no receptor cells -> can't detect light (the stimulus) -> can't see
• cornea = tough, clear covering over iris and pupil that protects eye. Light bends as it passes through this.
• retina (receptor) = the layer of light sensitive cells at back of the eye -> detects images focused by cornea + lens
• pupil = a dark circle in centre of your iris, a hole that lets light into the inner eye
• sclera = the thick, tough, white outer covering of the eyeball
• choroid (middle) = composed of layers of blood vessels that nourish back of the eye -> contains pigments to avoid internal reflection
• avoids internal reflection?

  choroid -> contains pigments
• optic nerve = bundle of nerve fibres that carry information from retina to brain
• carries information from retina to brain?

  optic nerve -> bundle of nerve fibres
• iris = effector (detects light -> contracts or none= relaxes)
• Iris = muscle that controls how much light enters the eye
• Blind spot = where optic nerve leaves the retina -> no light sensitive cells here -> light can't be detected -> can't see
• lens = clear, flexible structure that makes an image on eye's retina. Changes shape to focus on objects.
• how does the eye respond to an increase in light?

  receptor cells of retina detect increase in light intensity -> electrical impulse sent along sensory neurone in optic nerve to relay neurone in brain -> to motor neurone -> to effector (iris muscle) -> iris contracts -> makes pupil narrower -> less light now reaches retina
• eye reflex arc: stimulus (bright light) -> receptor cells (in retina) -> sensory neurone (in optic nerve) to brain -> relay neurone in brain to motor neurone (optic nerve) -> effector (iris muscle/eyelid) -> contracts to make pupil smaller/contracts to blink
• sensory neurone + motor neurone found on optic nerve
• sensory neurone = before motor
• motor neurone = after sensory
• relay neurone -> in brain