The nervous system is a collection of cells, tissues, and organs through
which an organism receives information from its surroundings and then
directs the organism as to how to respond to that information. As an
example, imagine that a child accidentally touches a very hot piece of
metal. The cells in the child's hand that detect heat send a
message to the child's brain. The brain receives and analyzes that
message and sends back a message to the child's hand. The message
tells the muscles of the hand to pull itself away from the heat.