Lumbar punctures are often performed in hospitals, however some neurologists now do them as outpatient operations in their offices. A thin, hollow needle is inserted into the lower section of the lumbar spine, commonly between the third and fourth or fourth and fifth lumbar vertebrae. The needle is used to remove fluid for testing under microscopic examination by a neuropathologist. The spinal cord begins at the bottom of the brain and continues all the way up to the neck. Any injury or disease that affects the spinal cord can cause pain, muscle weakness, loss of bladder or bowel control, even death. The nerves from the spinal cord branch out through openings in the bone called synapses, sending messages to other parts of the body when they are healthy. In cases of injury or disease, these nerves may be damaged causing pain, muscle spasms, poor reflexes, and sensory problems. Many diseases affect the nervous system, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS or "Lou Gehrig's disease"), multiple sclerosis, Parkinson's disease, and transverse myelitis. Other disorders include infections such as meningitis and HIV/AIDS-related dementia. Even normal aging can cause problems with thinking skills and judgment. A stroke results in damage to the blood vessels supplying the brain and sometimes causes paralysis on one side of the body.