nervous system

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The system of cells, tissues, and organs that regulates the body's responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun neuroanatomy An organ system that coordinates the activities of muscles, monitors organs, constructs and processes data received from the senses, and initiates actions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the sensory and control apparatus consisting of a network of nerve cells