The document discusses the five main sensory organs - skin, nose, tongue, ear, and eye - and their functions in detecting touch, chemicals, sound, and light. It explains that the human nervous system is responsible for detecting stimuli, sending that information to the brain for interpretation, and then sending instructions from the brain to the body to respond. The central nervous system consists of the brain and spinal cord, while sensory nerves carry signals from receptors to the brain and motor nerves carry signals from the brain to muscles and glands.