The peripheral nervous system (PNS) consists of which nerves?

• A. Brain and spinal cord
• B. Nerves outside CNS
• C. CNS and PNS
• D. Peripheral nerves only

Answer: (B)

The peripheral nervous system is defined by location: all neural tissue outside the brain and spinal cord. So the nerves that carry signals between the central nervous system and the rest of the body—outside the CNS—make up the PNS. The brain and spinal cord are part of the CNS, so naming them as PNS would be incorrect. Saying “CNS and PNS” would incorrectly include the CNS as part of the PNS, which isn’t right. While “peripheral nerves only” points to nerves outside the CNS, the clearer description of the PNS is the nerves located outside the CNS, since that defines its full scope. In short, nerves outside the CNS are the peripheral nervous system.