L3 - The Eye

• Cornea


  A tough, clear covering over the iris and the pupil that protects the eye. Light bends as it passes through this.
• Retina (receptor)


  The layer of light sensitive cells at the back of the eye. This detects images focused by the cornea and the lens.
• Pupil


  A dark circle in the centre of your iris. It's a hole that lets light into the inner eye.
• Sclera


  The thick tough, white outer covering of the eyeball (outer)
• Choroid


  The is composed of layers of blood vessels that nourish the back of the eye. Contains pigments to avoid internal reflection (middle)
• Optic Nerve


  The bundle of nerve fibres that carry information from the retina to the brain
• Iris (effector)


  A muscle that controls how much light enters the eye
• Blind spot


  The place where the optic nerve leaves the retina. There are no light sensitive cells here.
• Lens


  A clear, flexible structure that makes an image on the eye's retina. It can change shape to focus on objects.
• Receptor cells of retina detect increase in light intensity. Electrical impulse sent along sensory neurone in the optic nerve, to a relay neurone in the brain, to a motor neurone to the effector (iris muscle). Less light now reaches the retina.
• Eye reflex arc:

  • Stimulus (bright light)
  • Receptor cells (retina) Sensory neurone (in optic nerve to brain)
  • Relay neurone (in brain)
  • Motor neurone (from brain to optic nerve)
  • Effector (iris - muscle contracts to make pupil smaller)/(eyelid - muscle contracts to blink)