The peripheral nervous system includes the nerves and signals of the sympathetic nervous system and the automatic nervous system.

The central nervous system (CNS) consists of the brain, spinal cord, spinal fluid and neurons, which transmit signals from the brain to other body organs.

The lymphatic system the body's secondary circulatory system. Its functions are closely linked to the functions of the body's primary circulatory system, the blood circulation. Organs and cells of the lymphatic system play an integral role in supporting the immune system, which is a functional system consisting of cells (e.g. blood cells which fight infection) and molecules (e.g. antibodies which protect against particular diseases). Unlike other body systems the immune system has no organs.