Quick Answer. Voltaire wrote Candide as a satire of the then-prevalent philosophical optimism advanced by Gottfried Wilhelm Leibniz. Voltaire, moved by contemporary events like the Seven Years' War and the 1755 Lisbon earthquake, felt that optimism was a naive way of viewing the world.
Neurons carry impulses from one place to another, around the many parts of the nervous system. They connect receptors to the central nervous system and also connect one part of the nervous system to another, for example in the brain and spinal cord.
The information that your neurons transmit comes from many sources. Let's use a finger touch as an example. When you touch something with your finger, nerve impulses immediately fire from your finger, to your brain. These impulses travel from one neuron to the next astonishingly quickly.