Neurology is a branch of medicine that deals with the study and treatment of disorders of the human nervous system. Such disorders can cause dysfunctions of the brain, spinal cord, peripheral nerves, or cranial nerves. They may result in symptoms like paralysis, headaches, muscle weakness, loss of sensation, seizures, or mental illness. The causes of neurologic disorders include drug and alcohol use, smoking, stress, genetic factors, physical injuries, and vitamin deficiencies. Treatments used in neurology include deep brain stimulation, medications, surgeries, therapies, and psychological treatments.