The nervous system coordinates almost everything that the human body does. Using the senses to receive information, the nervous system is able to initiate a response to any stimuli. It is the nervous system that is the means of receiving, analysing and responding to these stimuli. The human nervous system actually consists of the central nervous system (which is the brain and spinal cord) and the peripheral nervous system (that connects the central nervous system with the rest of the body). Some of the responses the nervous system makes are under our control; others are automatic and ensure that the other body systems continue to run well. The nervous system contains nerves; these are bundles of long, thin cells called neurons that carry electrical signals to and from the brain. There are three types of neuron:
- sensory neurons that carry signals from the body to the brain or spinal cord;
- motor neurons that carry signals from the brain or spinal cord to the muscles;
- association neurons that carry messages between sensory neurons and motor neurons.