Brain and spinal cord together constitute the central nervous system (CNS). The nerves of the CNS are located in the midline (central location) of the body.
The main function of the central nervous system is to coordinate all the body activities according to the sensory information sent by different organs.
The nerves of the peripheral nervous system (PNS) are projected out from the CNS and have a peripheral location. Some of the activities of peripheral nervous system are under the control of will. For example, some of the reflex activities can be controlled by will.
Thus, the blanks can be filled with central nervous system (CNS); peripheral nervous system (PNS).