Concept preview

What you will be able to do

1. 01Describe the central nervous system: the roles of the cerebrum, cerebellum, brainstem and spinal cord.
2. 02Distinguish the somatic and autonomic divisions of the peripheral nervous system.
3. 03Compare the sympathetic ('fight or flight') and parasympathetic ('rest and digest') systems.
4. 04Trace the reflex arc and explain why reflexes bypass the brain.

Having seen how single neurons fire and connect, we can now step back and look at the whole nervous system as an organised structure. It is built from two great divisions. The central nervous system (CNS) is the control centre: it consists of the brain and the spinal cord, the places where information is processed, decisions are made, and memories are stored. The peripheral nervous system (PNS) is everything else — the vast web of nerves that fan out from the brain and spinal cord to reach every corner of the body. The PNS is the communication network, carrying sensory information inward to the CNS along sensory neurons, and carrying commands outward from the CNS along motor neurons. Think of the CNS as the head office where decisions are taken and the PNS as the phone lines and messengers that connect that office to the whole company. Every experience you have and every movement you make is a conversation between these two divisions, running many times a second.