1 Assumed Knowledge 2 Receptors 3 Communication 4 Light and Photoreceptors 5 The Human Eye 6 Range of Electromagnetic Radiation Detected 7 Refraction of Light 8 Sight Defects 9 The Retina 10 Play – Inside the Eye 11 Colour Blindness 12 Colour for Communication 13 Sound 14 The Larynx 15 Other Animals Make Sounds 16 The Ear 17 Hearing Aids 18 Nerves 19 The Action Potential 20 The Brain 21 The Brain Interprets Signals