Explain what type of stimulus each sense organ responds to and how.

The sense organs contain receptors that are sensitive to stimuli.

The nervous system consists of the central nervous system - brain and spinal cord -and peripheral nerves. Nerve impulses travel through the axons of neurones - nerve cells. Reflex actions are fast, automatic and protective responses.

Human vision is binocular, which gives us a good perception of depth. Vision defects include short-sightedness, long-sightedness and colour blindness.