The largest part of the brain is a pair of hemispheres that conduct thought and integrate information from the senses . Some nerves connected to the cranial and spinal nerves form the autonomic nervous system - one set of these nerves handles stress and another group directly controls most of the organs of the body. The system provides us with all our links to the world outside our bodies, integrates the information received, and directs the organs to change in response to the information. Conditions that affect the nervous system Many of the diseases that affect the nervous system have their expression in other parts of the body. Conditions that affect the brain , such as alcoholism , Alzheimer's disease , cerebral palsy , or mental illness may produce various physical as well as mental effects.
Some infections directly attack the nervous system, including encephalitis and meningitis .
One infection that may strike almost any organ, including the parts of the nervous system, is syphilis . In a sense, however, all symptomatic diseases attack the nervous system because one would feel no pain or develop no fevers or other observable symptoms without messages passing through the nerves .