Neurophysiology is a branch of physiology and neuroscience that is concerned with the study of the functioning of the nervous system. Neurophysiology or electro diagnostic testing refers to specialized investigations used in the diagnosis and prognosis of peripheral nervous system disorders. It is broadly defined as the study of nervous system function. In this field, scientists investigate the central and peripheral nervous systems at the level of whole organs, cellular networks, single cells, or even subcellular compartments. A branch of neurophysiology describes the function of the major system components of the nervous system of the human body at the system level. The overall nervous system of the body consists of the central nervous system (CNS), and the peripheral nervous system(PNS). The neurophysiology of the CNS studies the function of the brain and spinal cord while that of the PNS studies the function of all the nerves that connect the CNS with organs, muscles, blood vessels and glands. The neurophysiology of the PNS further subdivides into the somatic nervous system (SNS) and the autonomic nervous system(ANS), with the ANS being further divided by function into the sympathetic and parasympathetic systems.