Briefly outline the divisions and roles of the human nervous system.

The role of the nervous system is to collect, process and respond to information in the environment and to coordinate the workings of organs and cells in the body. It is subdivided into the central nervous system and the peripheral nervous system. The central nervous system is composed of the brain and spinal cord. The brain is the control centre for all the body's functions while the spinal cord is responsible for reflex actions and passing messages to and from the brain and connecting nerves to the peripheral nervous system. The peripheral nervous system transmits messages, via neurones, to the central nervous system from the outside world and from the central nervous system to muscles and glands in the body. It is subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system controls muscle movement and the autonomic nervous system controls involuntary vital functions. The autonomic nervous system is further subdivided into the sympathetic and parasympathetic nervous system. The sympathetic nervous system triggers the "fight or flight" response while the parasympathetic nervous system acts antagonistically and restores the "rest and digest" response.