The eye

• The nervous system enables humans to react to their surroundings and coordinate their behavior
• The nervous system comprises millions of neurones and uses electrical impulses to communicate quickly
• The eye is a sense organ containing receptors sensitive to light intensity and color
• Structure and function of the eye:

  • Cornea: refracts light as it enters the eye
  • Iris: controls the amount of light entering the pupil
  • Lens: further refracts light to focus it onto the retina
  • Retina: contains light receptors
  • Optic nerve: carries impulses between the eye and the brain
  • Sclera: tough white outer layer that protects the eye from injury
• Light receptors in the retina:

  • Rods: more sensitive to light, useful for dim light
  • Cones: produce color vision, three different types
• Pupil reflex:

  • Controlled by a reflex action
  • Size of the pupil changes in response to bright or dim light, controlled by the muscles of the iris