Neurology is concerned with the diagnosis and treatment of diseases and disorders of the nervous system. This covers the central nervous system (CNS, the brain and spinal cord) and the peripheral nervous system (PNS, the nerves outside of the brain and spinal cord). The main function of the PNS is to connect the central nervous system to the limbs and organs. The autonomic nervous system (ANS) is part of the PNS. It acts as a control system, functioning mainly below the level of consciousness, and affecting such things as heart rate, digestion, breathing rate, perspiration and others. Neurologists often specialise in different sub-fields as there are a large number of disorders and diseases affecting the nervous system, some common but many rare. Abnormalities in the brain, spinal cord or nerves leading to or from them may result in symptoms such as muscle weakness, paralysis, poor coordination, loss of sensation, seizures, pain and altered levels of consciousness. Treatment varies, but may include preventative measures, lifestyle changes, physiotherapy, pain management, medication and surgery.