Answer: Brain, spinal cord, and nerves
Explanation: The nervous system has two main divisions: the CNS and PNS. The Central Nervous system (CNS) is made of the brain and spinal cord, and the Peripheral Nervous system (PNS) is made of all the peripheral nerves that branch off from the spinal cord and exit to all parts of the body.
The heart is wrong because it is part of the cardiovascular system.
Psychiatry is wrong because it is a discipline, not an organ.