Physiology is concerned with the internal workings of the body, including functions such as metabolism, respiration and reproduction. Neurophysiology deals with how the nervous system (the brain, spinal cord and nerves) works. It is a broad area and may involve the molecular, chemical, electrical and biophysical nature of the nervous system. Clinical neurophysiology often involves testing the electrical functions of the brain, spinal cord and the nerves in the limbs and muscles. This is done to help in the diagnosis of a wide range of conditions affecting these parts of the body.