Nervous system is defined as all the cells, tissues and nerves that coordinate responses to internal and external stimuli.
An example of the nervous system is what tells the brain to react when you cut your finger while chopping vegetables.
all the nerve cells and nervous tissues in an organism, including, in the vertebrates, the brain, spinal cord, ganglia, nerves, and nerve centers: it coordinates and controls responses to stimuli and conditions behavior and consciousness
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.