The nervous system works by absorbing information through the senses, processing that information through a central brain, and using the information to trigger reactions throughout the rest of the body. The billions of nerve cells, called neurons, that are connected to each other and to other cells in the body transmit the information. In terms of function, the nervous system can be separated into the voluntary and involuntary nervous systems.
Each neuron has a short extension, called a dendrite, that acts like an antenna to receive information into its cell body. It also has a longer extension, called the axon, that can be a meter long and transmits the information. The brain is composed of over 100 billion neurons. The brain and the spinal cord are part of the central nervous system, which is named for its central location in the body. The peripheral nervous system is composed of all the other nerves in the body. The voluntary nervous system is consciously controlled and allows for the movement of arms and legs. The involuntary nervous system regulates processes in the body such as breathing, heart rate and sweating. This regulation is done by receiving signals from the brain and transmitting it to the body cells. Information such as how hungry a person is can also be transmitted from the body back to the brain.