1) A receptor (e.g. skin) detects a stimuli (e.g a sharp pin).
2) A sensory neurone transmits an electrical impulse across a synapse, impulses can't jump a synapse so they chemically diffuse across the gap, to central nervous system (spinal chord).
3) A relay neurone transmits the impulse on, to a motor neurone across a synapse.
4) A motor neurone is stimulated, the mipulse is then sent on to the effector (e.g. Muscle)
5) Action is taken (e.g. The muscle contracts and moves hand away from pin)