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.
Neurons transmit electrical impulses by allowing the passage of charged ions across their membranes in response to stimuli, changing the charge of the neuron in a process that propagates through the axon of the neuron. Normally, neurons maintain an internal negative charge relative to their environment by excluding sodium ions from their cytoplasm.